1

VARIABILITY AND ASSOCIATION AMONG BULB YIELD, QUALTIY AND RELATED TRAITS IN ONION

(Allium cepa. L.)

A THESIS PRESENTED TO THE SCHOOL OF GRADUATE STUDIES

ALEMAYA UNIVERSITY

IN PARTIAL FULFILMENT OF THE REQUIREMENTS

FOR MASTER OF SCIENCE DEGREE IN AGRICULTURE

(HORTICULTURE)

BY

ABAYNEH MELKE WOLDEGEBRIEL

3.1. JUNE, 2001

2

School of Graduate Studies Alemaya University

Title of Thesis

Variability and Association Among Bulb Yield, Quality and Related Traits in Onion (Allium Cepa L .)

By

Abayneh Melke Woldegebriel

Approved by Board of Examiners:- Prof. H. Ravishanker ___________________ Chairman Signature Prof. V.P. Gupta _____________________ Advisor Signature ____________________ _____________________ Co- Advisor Signature ___________________ ______________________ Internal Examiner Signature ___________________ ______________________ External Examiner Signature

3

Biographic Sketch

Abayneh Melke Woldegebriel was born in 1972 in Lomma Wereda, North Omo Administrative

region, Ethiopia. From 1977 to 1980, he attended elementary school at Lomma elementary school,

from 1981 to 1987 Junior secondary and comprehensive secondary school at Waka Senior Secondary

School. In 1987/88 he joined Alemaya University of Agriculture and graduated with B.Sc. degree

in August 1993 majoring in plant sciences. After graduation in December 1994 he was employed by

Southern Regional State Bureau of Agriculture and has worked as an agronomist in the North Omo

Zone Department of Agriculture.

He joined the school of Graduate Studies, Alemaya University of Agriculture, for M.Sc. Degree in

Horticulture in September 1999.

4

ACKNOWLDGEMENTS

This work was made possible through the combined efforts and positive attitudes of many kind-

hearted persons all of whom I thank very much. I shall only mention few names among theses: I am

very grateful to my research advisors; Prof. H. Ravisohankar (Professor of Horticulture, Alemaya

University) and Prof. V.P. Gupta (Professor of Biometrics, Alemaya University) whose continued

guidance, inspiration, encouragements and support throughout my study period made the completion of

this study smooth and successfully.

My special thanks go to the staff members of Horticulture section of Plant Sciences Department,

with especial mention of Ato Yibekal Alemayheu, Getu Beyene, Teferi Yehsitela and all field

assistants for their dedicated assistance, encouragement and ever ready help through the entire period

of this work.

The assistance given by Southern Regional State Bureau of Agriculture and North Omo Zone

Department of Agriculture is duly acknowledged.

I am highly indebted to Ato Kebede W/Tsadik and Ato Tekalign Tsegaw Staff members,

Horticulture section, Plant Sciences Department for their dedicated help in mobilizing and organizing

all the necessary facilities that enabled me to accomplish this work successfully.

Grateful acknowledgements are also due Ato Yoseph Mekasha (Assistant Research Director, AU)

for his strong moral and material support and continuos encouragement during the study period. My

heart felt thanks go to Ato Tesfahun Alemu for his friendly cooperation during the thesis work.

The cooperation extended to me by Fleke Asrat, Eshetu Eltamo, Abush Tesfaye, Baye Berihun,

Gizachew W/Michael, Million Tadese, Shimelis Feleke and all my colleagues are also highly

appreciated.

My thanks are also due to Dr. Habtamu Zeleke Ato Mulugeta Assefa (Chemistry Department,

AU), and Ato Yoseph Beyene for their encouragement and material assistance.

5

The effort made by the school of graduate studies and AU Research Office in facilitating this work

are also gratefully acknowledged.

Finally I wish to express my deep appreciation to my wife w/o Hizbayehu Teshale for the affection

understanding and patience during the entire study period.

6

VARIABILITY AND ASSOCIATION AMONG BULB YIELD, QUALTIY AND RELATED TRAITS IN ONION (Allium Cepa L.)

By Abayneh Melke, BSC (AUA)

Research Advisors: Prof. H. Ravishankar (Ph.D.) Prof. V.P. Gupta (Ph.D.)

ABSTRACT Twenty four onion (Allium cepa L.) germplasm lines and two local cultivars used as checks were evaluated to obtain information on genetic variability and association of different characters with bulb yield, quality and among themselves at Alemaya University, Ethiopia. Wide range of variability was obtained for the traits studied viz., plant height, leaf length, number of leaves, leaf diameter, neck thickness, bulb diameter, bulb length , bulb dry weight, total soluble solids, pungency, fresh and dry weights above ground, yield per plant, harvest index per plant and biological yield per plant. The estimates of phenotypic coefficient of variation were high as compared to genotypic coefficient of variation in majority of the cases. Very high values of heritability were observed for fresh weight above ground (93.50 per cent) followed by yield per plant (90.89 per cent), bulb dry weight (90.42 per cent) and leaf diameter (90.16 per cent). Other characters which showed high heritability included harvest index (89.0 per cent), biological yield (86.98 per cent), dry weight above ground (88.4 per cent), pungency (88.67 per cent), soluble solids (89.63 per cent and, number of leaves (87.62). High heritability value coupled with high genetic advance were observed for number of leaves, leaf diameter, bulb dry weight, soluble solids, pungency, dry weight above ground and yield. Bulb yield showed positive and significant phenotypic asso ciation with plant height, leaf length, leaf diameter, neck thickness, fresh and dry weights above ground, harvest index and biological yield. The correlation coefficients of these traits with bulb yield at genotypic level were also high. Path coefficient analysis revealed harvest index per plant, biological yield, plant height, leaf diameter, neck thickness and bulb dry weight to have positive direct contribution to bulb yield at phenotypic level where as dry weight above ground, leaf diameter, plant heig ht, number of leaves, harvest index per plant and biological yield per plant showed positive direct effect at genotypic level.

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DECLARATION I, the undersigned declare that the thesis is may original work and all sources of materials are duly acknowledged. Name : Abayneh Melke Signature : ______________ Place of submission: Alemaya University Date of Submission: June, 2001

8

1. INTRODUCTION

Onion (Allium cepa L.) belongs to the genus Allium of the family Alliaceae (Hanelt, 1990). Onion

is by far the most important of the bulb crops cultivated commercially in nearly most parts of the

world (Simon, 1992). The crop is grown for consumption both in the green state as well as mature

bulbs. Onions exhibit particular diversity in the eastern Mediterranean countries, though Turkmenia,

Tajikstan to Pakistan and India which are the most important sources of genetic diversity (Astley et

al., 1982). .Allium are typically plants of open, sunny, dry sites in fairly arid climates, however many

species are also found in the steppes, dry mountain slopes, rocky or stony open sites, or summer dry,

open, scrubby vegetation (Hanelt, 1990). They are weakly competitive and therefore are not normally

found in dense vegetation (Corgan and Kedar 1990).

Jones and Mann (1963) suggested the characters useful in identifying Allium cepa L. as compared

to other vegetable Alliums. Thus the common onion, (Allium cepa L.) including shallot has diploid

chromosome number, 2n =16, differing widely in respect of storage organs (foliage leaf bases and

swollen, bladeless inner sheaths); time of flowering (spring to early summer); flower color (white,

green striped); order of opening of florets in umbel (irregular), and bulbils in inflorescence (absent in

most cultivars). Onions being cultivated for so long, their bulbs and inflorescence development must

have been closely adapted to temperatures and photoperiods prevailing in regions of culture , there

existed a huge range of cultivars and land races, developed over centuries to fit into diverse climates

and food preferences of the world (Astley, 1990). Onions are grown for a variety of purposes as

fresh shoots for green salad and as bulbs for consumption uncooked; consumption cooked; pickling;

use in factory made food; dehydration; seed production and sets. Specific varieties have usually been

developed for those purposes, for example cultivars for dehydration have a higher bulb dry matter.

Bulbs for consumption uncooked are frequently sweet, mild -flavored and large, with single centers

suitable for making onion rings. A particular type for pickling is the small, white skinned silver

skin. On the other hand, bulbs for pickling cooked consumption, and for use in food manufacture

could be the small, medium, large and damaged grades respectively, from a crop of the same cultivar.

Normally, bulb production is

targeted at one of these outlets by controlling bulb size by varying the plant density (Mondal, et al.,

9

1986).

Alliums are characterized by the presence of sulfur containing compounds, which gave them their

distinctive smell and pungency (Block, 1985; Fenwick and Hanley, 1985a). Onion pungency

developed when allinase enzyme interacted with the sulfur containing amino acids, S-methyl -L-

cysteine sulfoxide, S-propenyl -L- cysteine sulfoxide and S-propyl -L- cysteine sulfoxide upon cutting

or crushing of onion tissue (Lancaster and Boland, 1990).

In Ethiopia, the Allium group (onion shallot and garlic) is the important bulb crops produced by small

farmers and commercial growers for both local use as well as for export. Among these crops, onion

though a recent introduction is rapidly becoming a popular vegetable among consumers. Statistics on

the production and extent of this crop though is not available, except that they are reported to be

grown in substantial amounts and are spread throughout the country being cultivated under both

irrigated as well as rainfed conditions in different agro- climatic regions (Lemma and Herath, 1992).

The majority of traits including most of those important to crop productivity, are controlled by the

combined effects of a number of genes which influenced the trait, each of which had a similar small

influence (Pike, 1986). A review of the breeding techniques applied to onion considered certain

explicit goals or objectives, like high yield, a nutritious end product, and pest and disease resistance to

be universally desirable (Dowker, 1990). Others, like color and shape of onion bulbs, are determined

by the local preferences. Objectives of the later sort will often vary with locality and with the market

niche identified for the improved variety. The desirable traits considered in cultivars grown for bulbs

included uniformity of bulb size, shape, color, date of maturity, high yield, disease and pest resistance,

bolting resistance, intact attractive skins, thin necks, single centered bulbs (freedom from double and

split bulbs) and firm flesh (Rabinowitch, 1988).

Considering the importance of onion as one of the potential vegetable crops for both internal

consumption as well as export, it is imperative to increase its productivity along with desirable

attributes through genetic manipulation. The genetic improvement of any crop plant needs to have a

knowledge on the nature and magnitude of variability present in the base population (Welsh, 1981 and

Dudley, 1997). Besides, the information on the association among various yield and related traits along

with quality is also required for indirect selection to obtain highly productive varieties with most of the

10

desirable traits required for consumer preference (Bhatt, 1970). Such information in onion are lacking

in Ethiopia which can greatly help in effective utilization of onion germplasm lines by selection or

hybridization.

Therefore, the present study was conducted by evaluating 26 germplasm lines for the genetic

improvement of onion with the following objectives;

1. To study the nature and magnitude of parameters of variability for bulb yield, quality and

related traits and,

2. To determine the association among bulb yield, quality and related traits.

11

2. LITERATURE REVIEW

2.1. Variability

Variation is the occurrence of differences among the individuals due to the differences in their genetic

composition and/or the environment in which they were raised (Allard, 1960). Information on the

nature and magnitude of genetic variability greatly helps in formulating sound crop breeding program

(Dubley and Moll, 1969).

2.1.1. Phenotypic and Genotypic Variation

The amount of genetic and phenotypic variability that existed in a species is of utmost importance in

efforts towards initiating a breeding program and developing better varieties in any crop. Genetic

variability is of immense importance to the breeders because it could be transmitted to the progeny

and the proper management of this diversity could produce permanent gain in the performance of the

plant (Welsh,1981).

Barta et al., (1983) reported that the attributes showing high estimates of variability were earliness,

bulb size , dry matter content and bulb weight and suggested that high coefficient of genetic variance

for yield components could be used to improve cultivars for almost all the characteristics studied.

2.2. Heritability

Heritability (broad sense) as defined by Allard (1960) is the proportion of genotypic variance to total

phenotypic variance expressed in per centage. Heritability estimates of factors controlling

agronomically important characters, especially those closely correlated with yield, have much

significance in plant breeding programs.

The estimate of heritability by different authors varied for the same trait. Normally, the heritability

values for quantitative characters are low owing to their sensitivity to environment (Allard 1960).

Heritability estimates varied not only with the environment but also with the nature of the test

12

population (Briggs and Knowles, 1967). In Allium cepa, bulb diameter, bulb weight, bulb thickness,

leaf length and days to flower were highly heritable (Singh, 1981)

Mc Collum (1968) reported negative genetic correlation between soluble solids and bulb size. Warid

(1952) also found high heritability (71 per cent) and concluded that four to ten gene pairs and partial

dominance of low soluble solids were involved in his cross studied in the green house. Owen (1961)

postulated that commulative gene action and a relatively small number of genes were involved in

soluble solids inheritance.

The inheritance of pungency was studied by Pal and Singh (1988) using parental and F1 data from

eight parent diallel crosses .They reported that pyruvic acid was controlled by additive and dominant

gene action with additive gene action more important. Because of the relationships between low

pungency, low dry matter, poor storage quality, and susceptibility to neck rot, the development of mild

onions with good keeping quality is a challenge for breeders.

2.3. Expected Genetic Advance

Genetic advance measures the expected genetic progress that would result from selecting the best

performing genotypes for a character being evaluated (Allard, 1960). Genetic advance under selection

indicates measure of the difference between the mean genotypic value of the selected population over

the mean genotypic value of the original population for a given character (Allard,1960). Heritability

value in itself provide no indication of the amount of genetic progress that would result from selecting

best individuals . High heritability value could be obtained with genotypes having small or large

genetic variance but genetic progress would be larger with larger genotypic variance (Johnson et al.

1955 and Allard, 1960). Genetic coefficient of variation together with heritability estimate would seem

to give the best picture of the amount of advance to be expected from selection (Johnson and

Hernandez, 1980).

In Allium cepa, high estimates of heritability and genetic advance were recorded with respect to bulb

weight, leaf length, number of leaves and bulb diameter (Dowker, 1990), where as in Allium

sativus, high value of expected genetic advance were reported for number of cloves per bulb and

13

weight of cloves (Korla et al., 198l)

2.4. Association of characters

2.4.1. Correlation Analysis

Association of characters among yield, its components, and other economic traits is important for

making selection in breeding program and combining several desirable attributes. It suggests the

advantage of a scheme of selection for more than one character at a time. The correlation between

characters may arise from linkage or from developmental genetic interactions, with or without a

purely phenotypic component (Simmonds ,1986). To facilitate selection in breeding for high yield, it is

logical to examine various components and give more attention to those having the greatest influence

on yield. In correlation studies ,it is customary to emphasize large number of plant characters

examined in a large number of varieties and use the correlations to establish an index in deciding the

direction of selection.

Genotypic correlation coefficients provided a measure of genetic association between traits in order to

identify the important traits to be considered in a breeding program (Pandey and Gritton ,1975). In

Allium cepa, yield was positively correlated with leaf length (Dowker et al., 1976 ). Patil et al.,

(1985) reported that there was a positive association between neck thickness and bulb diameter. As it

is true in any crop, selection based on any single plant attribute is unlikely to lead to dramatic

improvements in the yield potential of Allium cepa and it is suggested to use alternative selection

criteria based on physiological or morphological characteristics which contributed to improved yield

potential (Moot and Mc Neil ,1995).

2.5. Path Coefficient Analysis

14

The correlation coefficient becomes more evident when genotypic correlations are partitioned into its

components in the path analysis in order to determine the relative magnitude of various attributes

contributing to correlation. Path coefficient provides an effective means of entangling direct and

indirect causes of association and measures the relative importance of each causal factor ( Dewey

and Lu, 1959). This method of path coefficient was emphasized on partitioning of total correlation into

direct and indirect effects that is worthwhile for an effective selection program.

In Allium cepa, weight of bulb, plant height and bulb diameter contributed directly towards yield

whereas diameter of bulb and plant height contributed maximum via weight of bulb (Kalloo et al .,

1982 ). Thus, it is evident that selection based on these traits would improve the yield potential of

onion.

2.6. Flavor and Odour

Onion pungency was estimated by analyzing enzymatically produced pyruvic acid (Schwimmer and

Weston, 1961). This acid is produced by allinase hydrolysis of a group of flavor- precursor S-alk (en)

yl -L - cystein sulfoxides in onion tissues when they are mechanically chopped or macerated. Many

sulfur volatiles and ammonia also are produced during this reaction . A high correlation between

enzymaticaly produced pyruvic acid and pungency perception was reported (Schwimmer and

Weston ,1961; Waller and Corgan, ,1992). Thus pyruvic acid concentration is suggested as a mildness

selection criterion in onion breeding (Waller and Corgan ,1992)

Breeding onions for desired pungency requires reliable methods for discriminating between individuals

in a population. Organoleptic evaluation has been used traditionally in onion breeding programs

however, it lacked precision and repeatability, especially while evaluating highly pungent onion

(Lancaster and Boland 1990; Whitaker, 1976). These authors also indicated that pungency and other

flavors formed from the hydrolysis of S-alk (en) yl cysteine sulfoxide precursor molecules by allinase

following cell disruption. It has been shown that the content of pyruvic acid which developed through

enzymatic action within a few minutes after onion tissue is macerated is highly related to degree of

onion pungency (Bennet, 1945; Morgan, 1946; Schwimmer and Weston ,1961).

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3. MATERIALS AND METHODS

3.1. Testing Location

The study was carried out at Horticulture section's research field, Rare, Alemaya University. The

experimental site is located at Alemaya University campus at 420 3' E longitude, 90 26' N latitude at

an altitude of 1980 m.a.s.l. (Anon, 1990) . It is situated in the semi-arid tropical belt of eastern

Ethiopia . The soil of the experimental site was well drained deep alluvial with a sub-soil stratified

with loam and sandy loam that contained 3.05 per cent organic matter and 0.4 per cent nitrogen with

pH of 7.7 (Tamire, 1973). The mean annual rainfall was 780 mm and the mean annual

maximum/minimum temperatures were 23.40 and 8.250 C respectively.

3.2. Experimental Materials

Twenty four onion germplasm lines and two released local cultivars used as check constituted the

test material of the study. The introduced material represented the collections of different

geographical origins provided by the Asian Vegetable Research and Development Center (AVRDC)

, Taiwan along with local checks obtained from Melkassa Research Center, Ethiopian Agricultural

Research Organization. The details of the test material are presented in Table 1.

3.3. Experimental Design and Field Management

Seeds of each genotype were sown in rows 10 cm apart in nursery on well prepared seed-bed. At 3

to 4 leaves stage (50-60 days after nursery sowing), the seedlings were transplanted in the

experimental field. Planting was done on ridges of about 25 cm height adopting recommended spacing

of 40 cm between rows and 20 cm between plants in plots of 3m length. A distance of 0.6m was

maintained between plots. Each experimental plot consisted of 4 rows with 15 plants per row. The

trial was laid out in randomized complete block design with three replications.

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Table 1. Source, Description and Origin of the Test Genotypes

No Name/Identity Accession No Source Origin/Collection Region

1. AC2-I 1902 AVRDC, Taiwan Breeding lines of AVRDC

2. AC8-I 1908 AVRDC, Taiwan Breeding lines of AVRDC

3. AC11-I 1911 AVRDC, Taiwan Breeding lines of AVRDC

4. AC 383 I 1914 AVRDC, Taiwan Breeding lines of AVRDC

5. AC50-I 1924 AVRDC, Taiwan Breeding lines of AVRDC

6. AC 726(A0 C 9695 AVRDC, Taiwan Breeding lines of AVRDC

7. AC727(A0 C 9698 AVRDC, Taiwan Breeding lines of AVRDC

8. Yellow Granex -C-D-N 10002 AVRDC, Taiwan Breeding lines of AVRDC

9. Red Creole AC 461 AVRDC, Taiwan Variety from Nepal

10. Texas Grano 502 AC 469 AVRDC, Taiwan Variety from USA

11. Agrifound Dark Red AC 460 AVRDC, Taiwan Variety from India

12. Arka Niketan AC 464 AVRDC, Taiwan Variety from India

13. Regia AC498 AVRDC, Taiwan Variety from USA

14. XP 8403 AC499 AVRDC, Taiwan Variety from USA

15. Super High Gold No1 AC526 AVRDC, Taiwan Variety from Japan

16. Gladiator AC540 AVRDC, Taiwan Variety from Japan

17. Rouge De Tana AC566 AVRDC, Taiwan Variety from France

18. Cristal PRR AC567 AVRDC, Taiwan Variety from France

19. Kalipaitiya AC 595 AVRDC, Taiwan Variety from SriLanka

20. Bombay Red AC 748 AVRDC, Taiwan Variety from Tanzania

21. N53 AC 842 AVRDC, Taiwan Variety from India

22. White Hawk AC 843 AVRDC, Taiwan Variety from Holland

23.

24.

25.

26.

Sebaquena

Granex 429

Adama Red

Melkam

AC 892

Check

Local check

Local check

AVRDC, Taiwan

AVRDC, Taiwan

EARO, Ethiopia

EARO, Ethiopia

Variety from Nicaragua

F1 hybrid onion, AVRDC

Released local cultivars

Released local cultivars

17

The crop was fertilized with 300 kg/ha of P2O5 (in the form of DAP) at the time of transplanting

(Jackson, 1987). Other cultural practices like irrigation, weeding, and plant protection sprays to control

pests and diseases were carried out as and when required. Environmental conditions were fairly

conducive for downy mildew disease development. In order to protect the experimental materials

from the pathogen, systemic fungicide, Ridomyl was used on the crop regularly.

3.4. Data Collection

Observations on the following sixteen characters were recorded on five randomly taken plants from

each plot in each replication.

1. Plant Height (PH): the distance measured in cm from the soil surface to the tip of the mature

leaf in the plant.

2. Leav es per Plant (LP): total number of leaves per plant recorded at

physiological maturity .

3. Leaf Length (LL) : the average length of the longest leaf expressed in cm at

physiological maturity.

4. Leaf Diameter (LD): the diameter of the longest leaf at the time of maturity

expressed in cm.

5. Neck Thickness (NT): average wall thickness measured at the narrowest point expressed in

cm.

6. Bulb Length (BL): the height of the mature bulb measured in cm.

7. Bulb Diameter (BD): the average size measured at the widest point in the middle

portion of the mature bulb expressed in cm.

8. Yield Per Plant (YPP): the average weight of mature bulb expressed in gram.

9. Biological Yield Per Plant (BYPP): the total yield at the time of maturity expressed

in grams

10. Harvest Index Per Plant (HIPP): the ratio of mature bulb yield per plant to the

biological yield expressed in grams.

11. Fresh Weight Above Ground (FWAG): the total fresh weight of above

18

ground biomass of physiologically mature plant recorded in grams.

12. Dry Weight Above Ground (DWAG): the total dry weight of above

ground biomass of physiologically mature plant recorded in grams.

13. Bulb Dry Weight (BDW): the average dry matter weight of the mature

bulb expressed in grams.

14. Days to Maturity (DTM) : the actual number of days from seedling emergence to a day at

which more than 90% of the plants attained physiological maturity.

15. Total Soluble Solids (TSS): the amount of total soluble solids present in the bulb was

estimated using refractometer Bellingham and Stanley limited, UK (model 60/70) and expressed

as percentage.

16. Pungency (PCY): bulbs were evaluated for pungency by measurement of

enzymatically produced pyruvic acid values expressed as m mole pyruvic acid g-1.f.wt. The

detailed procedure followed is as follows:

Onion pungency was determined using the pyruvic acid estimation methods of Schwimmer and

Weston (1961). Dry outer scales of fresh onions were removed, and bulbs were cut equatorialy into

two halves . A control wedge was cut from the top portion of each bulb and 20g tissue was quickly

sliced into 60ml of 5% trichloro acetic acid (TCA) to inactivate the allinase in order to determine back

ground level of non- enzymatically produced pyruvic acid. After one hour, controls were blended for 3

minutes and filtered. Control filtrates were diluted ( 1:10 ) with distilled water and analyzed for non-

enzymatically produced pyruvic acid .

Sample wedges were blended with an equal volume of distilled water for 3 min, allowed to stay

covered for 5 min, filtered, and diluted with distilled water (1:20). Each reaction test tube contained

1ml each of diluted filtrate, distilled water and 2,4- dinitrophenyl hydrazine (0.0125% DNPH in 2 N

HCL ). A blank was prepared with 2 ml water and 1ml DNPH. All reaction test tubes were

vortexed and incubated in a water bath at 370C for 10 minutes. The reaction was then stopped by

adding 5ml of 0.6N NaOH and the test tubes were vortexed. The pyruvate was measured by reading

the absorbance at l = 420 nm wave length using a spectrophotometer Jenway Ltd. Felested,

Durrow, Essex, UK and model 6100 for both control as well as sample filtrates.

19

A standard curve for calibration was prepared with sodium pyruvate with gradient concentrations of

pyruvic acid. Final pyruvate concentration per bulb (m mole g-1.f.wt.) was calculated from the

difference between pyruvate levels in the sample and control wedges.

3.5. Statistical Procedures

3.5.1. Analysis of Variance

The data were subjected to analysis of variance for randomized complete block design as per Gomez

and Gomez (1984) and least significant difference (LSD) was used to separate the means at 1 per

cent and 5 per cent probability levels.

3.5.2. Phenotypic and Genotypic Variability

The variability present in the population was estimated by simple measures viz., range, mean,

standard error, phenotypic and genotypic variances and coefficient of variations. The phenotypic and

genotypic variances and coefficient of variations were estimated according to the following methods

suggested by Burton and De vane (1953).

d p2 = d g

2 + d e2

where d p2 = Phenotypic variance,

d g2 = genotypic variance and

d e2 = environmental variance (error mean square);

d g2

= d dt2 e

2

- r

where , d t2 = mean square of treatment and

r = number of replications;

20

PCV =( )d px

2

100_ *

where, PCV = Phenotypic Coefficient of variation and

_

x= population mean ,and

GCV=

( )d gx

2*100

_

Where GCV = genotypic Coefficient of variation

3.5.3. Heritability in the Broad Sense

Heritability on plot basis was calculated for each character based on the formula developed by Allard

(1960) as: H=d

dg

p

2

2 100 *

3.5.4. Expected Genetic Advance

The Genetic Advance (broad sense ) expected under selection assuming the selection intensity of 5%

was calculated by the formula suggested by Allard (1960):

Gs=(K)(dA) (H)

Where, Gs = expected genetic advance, and

K = the selection differential (K=2.06 at 5% selection intensity).

dA= phenotypic standard deviation

H = heritability.

21

3.5.4.1. Genetic advance as a per cent of mean

Genetic advance as a per cent of mean was estimated as :

GA * 100

_

x Where

_

x = Population mean

3.5.5. Correlation Analysis

Phenotypic correlation is the relationship between two variables, which includes both genotypic and

environmental effects, and genotypic correlation is the inherent association between two variables.

These were estimated using the formula suggested by Miller et al., (1958).

rp=( )

Pcov x.y

* d dg x pY2 2

rg=( )G

x yg

cov x . y

* gd d2 2

Where, rp = phenotypic correlation coefficient ,

Pcov x.y = phenotypic covariance between character x and y,

d p2 x = phenotypic variance for character x, and

d p2 y = phenotypic variance for character y;

rg = genotypic correlation coefficient,

Gcov x.y = genotypic covariance between characters x and y,

d g2 x = genotypic variance for character x, and

d g2 y = genotypic variances for the character y.

22

3.5.6. Path Coefficient Analysis

In path-coefficient analysis, bulb yield per plant was taken as the resultant (dependent) variable while

rest of the characters considered as causal (independent) variables. The direct and indirect effects of

the independent characters on bulb yield per plant were estimated by the simultaneous solution of the

following general formula suggested by Dewy and Lu (1959) :

rij = pij + Srik pkj where,

rij = mutual association between the independent character (i)

and dependent character (j) as measured by the genotypic

correlation coefficients,

pij = components of direct effects of the independent character (i) on

the dependent character (j) as measured by the genotypic path coefficients,

and

Srikpkj = summation of components of indirect effects of a given

independent character (i) on the given dependent character (j) via all other

independent characters(k).

To determine pij values, square matrices of the correlation coefficients between independent

characters in all possible pairs inverted and then multiplied by the correlation coefficients between the

independent and dependent characters using Agrobase statistical package. Residual effects were

estimated using the formula:

1-R2 where, R2= P ijrij

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4. RESULTS AND DISCUSSION

4.1. Analysis of Variance

The results on the analysis of variance using RCB design are presented in Appendix Table 2. It can

be seen that mean square due to germplasm lines were highly significant for all the traits studied

indicating the existence of sufficient genetic variability. The characters for which coefficient of

variation was slightly higher included bulb length, fresh and dry weights above ground, yield per plant,

harvest index per plant, and biological yield per plant but it was less than 20 per cent for the rest,

indicating the better precision of the experiment.

4.2. Variability Studies

The results of the present study on the estimates of range, mean, phenotypic and genotypic coefficient

of variations, phenotypic and genotypic variances, heritability in the broad sense, genetic advance and

genetic advance as a per cent of mean for the sixteen characters studied are presented in Table 2.

4.2.1. Estimates of Range and Mean

The maximum bulb yield per plant (306g) was recorded by the germplasm line Granex 429 while it

was the lowest (70g) in AC 11-I (Appendix Table 1).

24

Grouping of the germplasm lines based on dry weight revealed that 30, 50 and 20 per cent of the

germplasm could be categorized as high, medium and low, respectively. This result is in agreement

with the findings of Brewster (1990) that cultivars for dehydration had a higher bulb dry matter (13-20

per cent) than the normal ones (7-10 per cent). This is supported by the observation of Luh et al.,

(1975) indicating that onions with high dry matter are firmer and hence more resistant to damage

during transport and storage. Yamaguchi et al., (1975) observed that onions with high dry matter

content tended to yield less than those with low dry matter content, thus the cultivars with high dry

matter content may be less attractive to growers, particularly, to sell the crop at the green bulb stage

or as soon as it reached its maximum size.

With respect to maturity (Appendix Table 1), 38.5 per cent of the entries were observed to be early

maturing (105 -115 days), 50 per cent medium maturing (116 -119 days) and only 11.5 per cent late

maturing (120 -125 days). As regards pungency 19.4 per cent (pungent) of the germplasm lines

ranged between (0.136 -0.361m mol pyruvic acid g-1 fresh weight followed by 57.6 per cent

(moderately pungent) between (0.102-0.135 m mol pyruvic acid g-1 fresh weight) and the remaining 23

percent (mild pungent) ranged between (0.052-0.101m mol pyruvic acid g-1 fresh weight). This is in

conformity with the findings of Schwimmer and Weston (1961). In view of the increased demand

and market for moderately pungent onions, development of such cultivars is becoming an important

goal for breeders (Vavrina and Smittle, 1993). Onion breeders require an objective test to select for

pungency and currently, the pyruvic acid estimation is the best alternative to achieve this goal ( Waller

and Corgan, 1992). In the present study, this approach was adopted.

25

Table 2. Estimates of mean, range, coefficient of variation phenotypic (PCV) and genotypic (GCV) levels, phenotypic (s2p) and genotypic

(s 2g) variances, heritability in broad sense (h2), genetic advance (GA) and genetic advance as per cent of mean for various

characters.

Characters Range Mean SE PCV

(%) GCV (%)

s2P s2g h2 (%)

GA GA (as % of mean)

Plant height (PH) 53.0-80.4 64.22 2.92 14.45 12.10 68.98 60.45 87.62 14.99 23.34 Leaf length (LL) 43.7-68.4 53.97 2.90 16.47 13.58 62.14 53.69 86.39 14.03 25.99 Leaves /plant (LP) 10.9-35.5 19.29 1.97 32.07 26.76 30.52 26.64 87.29 9.94 51.50 Leaf diameter (LD) 1.5-3.8 2.45 0.18 25.62 22.24 0.328 0.296 90.16 1.07 43.49 Neck thickness (NT) 1.8-3.48 2.65 0.20 19.41 14.26 0.184 0.143 77.89 0.69 25.94 Bulb diameter (BD) 7.0-9.7 8.47 0.75 15.37 2.38 0.599 0.041 6.87 0.11 1.29 Bulb length (BL) 5.2-9.3 6.86 0.94 25.15 8.60 1.224 0.349 28.48 0.65 9.47 Bulb dry weight (BDW) 3.93-13.4 8.49 0.85 35.23 30.69 7.521 6.80 90.42 5.11 60.11 Total soluble solid (TSS) 6.2-15.0 10.25 0.76 25.43 21.90 5.624 5.04 89.63 4.38 42.73 Pungency (PCY) 0.056-0.36 0.107 0.01 32.73 27.83 0.00123 0.000887 72.11 0.058 53.98 Fresh weight above ground (FWAG)

105.5-581.5 260.36 37.9 60.72 55.24 21112.81 20679.48 93.50 286.46 110.02

Dry weight above ground (DWAG)

11.9-48.9 24.42 3.85 51.34 43.48 157.21 112.7773 71.73 20.57 84.21

Days to maturity (DTM) 105-125 117.69 3.03 6.29 4.44 36.46 27.282 74.83 9.31 7.90 Yield per plant (YPP) 70-306 1.66 0.23 48.00 42.08 0.538 0.489 90.89 1.38 82.66 Harvest index per plant (HIPP) 0.014 -0.12 0.055 0.13 51.86 44.29 0.000813 0.000593 72.94 0.047 86.07

Biological yield per plant(BY PP)

10.97-142.7 32.92 4.086 38.60 32.06 128.09 111.387 86.96 20.27 61.58

26

The higher per centage values of total soluble solids (Appendix Table 1) were recorded by the

germplasm lines Bombay red (11.03), Agrifound Dark Red (11.37), Red Creole (11.73), AC50-I

(12.13), AC726(A)-C (12.13), AC2-I (12.2) AC8-I (12.33), AC 383-I (13.33), AC 11-I (13.53),

Kalipitiya (15.00) and Adama Red (11.53). For the rest, the values ranged between ( 6.0-10.0)

indicating low soluble solids content.

Bulb yield per plant ranged between 168.3g and 306.7g for the top 12 high yielding entries (Appendix

Table 1). Among them, nine were observed to be medium maturing (116-119 days) indicating the

association of high yielding trait with medium maturity. Germplasm lines relatively longer period might

have developed good edible flesh over the early maturing ones and at the same time long maturing

ones might have faced terminal moisture stress. This is corroborated by the observations of Boswell

(1984). Maximum harvest index was recorded in respect of the germplasm lines AC498 (0.121),

AC567 (0.097), AC 496 (o.098),Granex 429 (0.085) and AC499 (0.080).

Bulb diameter higher than 6 cm was recorded for all the germplasm lines, except Bombay Red. Out

of the 26 germplasm lines, 57.6 per cent recorded above 60 cm plant height, whereas 42.4 per cent of

them had the height ranging between (50 59 cm). With regard to leaves per plant, 42.3 per cent of

the germplasm recorded more than 20 leaves per plant while 46.2 per cent had leaves ranging

between 14 -19. Leaf length ranged between 50 - 68.4 cm in 53.85 per cent of the germplasm. Leaf

diameter varied between 2 -3 cm in 80. 75 per cent of the lines. A bulb length of 6 to 9 cm was

recorded in 69.23 per cent of the germplasm lines.

Highest fresh weight and dry weight above ground biomass were recorded in respect of the lines

27

9695, 9698, AC 461, AC540, AC595 and Granex 429 (Appendix Table 1). They ranged between 350

- 581g for fresh weight per plant and 30 - 48g for dry weight per plant which accounted for 23 per

cent of the lines. Out of these, only Granex 429 was high yielder and the rest were poor in their bulb

yield. For majority of the lines, fresh weight above ground biomass ranged between 150 -349g and

dry weight above ground biomass ranged between 15 - 46 . 7 g and this represented 61.5 per cent of

the lines. Out of the 26 germplasm lines, 92.3 per cent had neck thickness ranging between 2. 13 -

3.49 cm.

Generally, the range of phenotypic variation was very high for all the characters considered, specially

for the characters like plant height, leaf length, leaf diameter, neck thickness, fresh weight above

ground, dry weight above ground, days to maturity and biological yield per plant while the remaining

traits showed less variability. Sufficient variability for days to maturity and other traits was also

reported earlier by Rabinowitch (1988) in onion.

4.2.2. Estimates of Phenotypic and Genotypic Variability

PCV was generally higher than GCV for all the characters considered (Table 2) but in majority of

the cases, the two values differed only slightly suggesting lesser influence of the environmental

factors. However , the differences between PCV and GCV for leaves per plant, neck thickness, bulb

diameter, bulb length, fresh weight above ground, dry weight above ground, yield per plant, harvest

index per plant and biological yield per plant were relatively wide indicating the influence of

environment in determining these traits. The ranges for PCV was 6.29 per cent in respect of days to

maturity to 60.72 per cent in case of fresh weight above ground and for that of GCV, it was 4.4 per

cent for days to maturity to 55.24 per cent in respect of fresh weight above ground biomass.

28

Maximum genetic variation was obtained for plant height, leaf length, leaf diameter, neck thickness,

fresh weight above ground, dry weight above ground, yield per plant, days to maturity and biological

yield per plant (Table 2) and these variations in characteristics may be attributed to the geographical

origin of the germplasm lines. This offers wide scope for selection among these characters. Moderate

PCV and GCV values were recorded for leaves per plant, bulb length, bulb diameter, bulb dry weight

and total soluble solids. These findings are in agreement with those of Singh (1981) who reported

moderate to high PCV and GCV for the above observations. Hence, these traits having considerable

genetic variability, offers good opportunity for crop improvement through selection. Days to maturity

showed the lowest PCV and GCV value indicating limited scope for improvement of this trait

through selection

Generally , PCV and GCV estimates were observed to be high for bulb yield per plant, harvest

index, fresh and dry weights above ground and biological yield per plant indicating high genetic

variability for effective selection.

4.2.3. Estimates of Heritability (h2) in Broad Sense

Burton (1952) suggested that genotypic coefficient of variation along with heritability estimates

would provide a reliable estimate of the amount of genetic advance to be expected through phenotypic

selection. Broad sense heritability (h2), an estimate of total genetic variance as a portion of the total

phenotypic variance, which was worked out in respect of the sixteen characters ranged from 6.87 to

93.50 per cent.

29

Higher heritability estimates (per cent) were obtained for fresh weight above ground (93.50 ), yield

per plant (90.89) , bulb dry weight (90.42) and leaf diameter (90.16) . The GCV value for these traits

were also high in magnitude (Table 2). Harvest index per plant (72.94 per cent), biological Yield per

plant (86.96), days to maturity (74.83), dry weight above ground (71.73), pungency(72.11), soluble

solids (89.63), neck thickness (77.89), number of leaves (87.29), leaf length (86.39) and plant height

(87.62) also exhibited high heritability estimates.

The above characters, therefore , may respond effectively to selection pressure . GCV and heritability

estimates were observed to be high for fresh weight above ground, plant height, leaf length, leaf

diameter, soluble solids, harvest index, yield per plant, bulb dry weight, pungency, dry weight above

ground, biological yield per plant which could be of much significance in selection. Low heritability

was recorded for bulb diameter and bulb length indicating limited possibility of improvement of these

characters via selection. Singh (1990) observed that if heritability of a character is very high around 80

per cent or more, selection for such a character should be fairly easy. This is because there would

be a close correspondence between the genotype and phenotype due to relatively small contribution of

the environment to the phenotype . But for characters with low heritability, say less than 40 per cent,

selection may be considerably difficult or virtually impracticable due to the masking effect of the

environment on the characteristics of germplasm.

In support to the findings of this investigation, Pike (1986) observed moderate to high heritability

estimates for bulb yield per plant, bulb thickness and leaf length in onion.

4.2.4. Estimates of Expected Genetic Advance (GA)

Heritability estimates though provide basis for selection based on the phenotypic performance, the

30

estimates of heritability and genetic advance should always be considered simultaneously as high

heritability is not always associated with high genetic gain (Johnson et al., 1955).

The expected genetic advance expressed as a per centage of the mean by selecting the top 5 per cent

(high yielders) of the germplasm lines, varied from 1.29 per cent for bulb diameter to 110.02 per cent

in fresh weight above ground (Table 2). This indicated that selecting the top 5 per cent of the base

population could result in an advance of 1.29 to 110.02 percent over the population mean.

Comparatively high expected genetic advances were observed for leaves per plant, leaf diameter, bulb

dry weight, soluble solids, pungency, dry weight above ground, yield per plant (Table 2). Hence,

selection for these characters is likely to be more effective, as high heritability values were associated

with high genetic advance in the present study. This could be due to the additive gene effects (Panse,

1957). In the present study, low values of genetic advance were recorded for bulb length, bulb

diameter and days to maturity. Therefore, it is imperative that selection of germplasm lines based on

phenotypic performance for these characters with low genetic advances would not be effective. This

finding is in harmony with that of Dowker (1990) who reported high genetic advance as a per cent of

mean for bulb weight, leaf length and leaves per plant. High heritability associated with high genetic

advance was also noticed for pungency, soluble solids, leaf diameter, leaves per plant, bulb dry weight

, fresh weight above ground, dry weight above ground, yield per plant, harvest index per plant and

biological yield per plant on single plant basis. This implied that the above characters are amenable for

selection.

4.3.Association of Characters

4.3.1.Estimates of Correlation Coefficients at Genotypic (rg) and Phenotypic

31

(rp)Levels

The results of the present study pertaining to variability indicated adequate variation among the

germplasm lines that could be considered to attempt a substantial improvement through selection for

any one of these traits. In such a conclusion however, the breeding problem is seldom simplified to

the extent that improvement is desired in a single character with a complete disregard to other

attributes. Investigating the possibilities of high yield through yield attributes, as primary interest in

crop improvement, therefore, requires understanding of the amount of the magnitude of correlations

among various yield traits.

Estimates of the phenotypic and genotypic correlation coefficients between each pair of the studied

characters are presented in Table 3. In majority of the cases, genotypic correlation coefficients were

higher in magnitude than the corresponding phenotypic ones, indicating inherent associations among

various characters . This is in general agreement to that reported by Padda et al. , (1973) in onion.

4.3.1.1. Correlation of Bulb Yield Per Plant with its Components

Bulb yield per plant showed positive and significant phenotypic association with plant height, leaf

length, leaf diameter, neck thickness, fresh weight above ground, dry weight above ground, harvest

index and biological yield per plant. The correlation coefficient of these

traits with bulb yield at genotypic level was also high (Table 3). This indicated the trend that

improvement of these characters could improve physiological capacity to mobilize and translocate

photosynthates to the organs of economic value, which in turn might have increased the bulb yield

resulting from positive association of these characters with yield as observed in the present study.

32

Similar result was reported by Fehr (1987). On the other hand, significant and negative phenotypic

and genotypic correlations were found between bulb yield per plant with bulb dry weight, days to

maturity and total soluble solids. These correlations suggested that the germplasm lines producing

relatively medium sized bulb could produce higher dry matter yield and soluble solids as compared to

the ones yielding large sized bulbs. This is in agreement with the findings of Darbyshire and Henry

(1979) who reported negative and significant correlation of bulb yield per plant with bulb dry matter

and soluble solids in onion germplasms having medium bulb size.

Harvest index per plant showed positive association with bulb yield per plant at both phenotypic as

well as gentoypic levels (Table 3). This facilitated identification of individual bulbs with good

performance during selection. These findings are in conformity with that of Padda et al., (1973).

A low magnitude of negative correlation was recorded between bulb yield per plant and leaves per

plant at both phenotypic as well as gentoypic levels manifested in the lengthening of vegetative period.

This has probably induce less bulbing in some germplasm lines. Similar observation was reported by

Brewster (1990).

33

34

Days to maturity also showed significant and negative association with bulb yield per plant at both

phenotypic as well as genotypic levels. This indicated that too early and late maturing germplasm lines

are low in their bulb yield. It is however, felt that selecting germplasm lines coupled with medium

maturity and moderate to high bulb yields could be profitable in onion improvement program. This is in

view of the observation that in onion, medium maturity is associated with high bulb yield (Pathak,

1994).

4.3.1.2. Correlation Among Other Characters

Many of the characters studied were either positively or negatively correlated due to the mutual

association with other characters (Table 3). Biological yield per plant recorded low magnitude positive

correlation with pungency (rg= 0.145) indicating that the increase in total

biological yield per plant resulted in minimum contribution to pungency. Pungency also showed

significant positive correlation with fresh and dry weights above ground.

Biological yield per plant also showed significant positive correlation with plant height (rg= 0.601), leaf

length (rg=0.607), leaves per plant (rg=0.495), leaf diameter (rg= 0.537), neck thickness (rg= 0.622),

soluble solids (rg= 0.274), fresh weight above ground (rg=0.973), dry weight above ground (rg=0.967)

and days to maturity (rg= 0.6006). This is suggestive that the increment in biomass production is a

consequence of long phenological period and giant plant morphology. Harvest index showed negative

and significant association with biological yield (rg=-0.369). This indicated that biological yield

increased at the expense of bulb yield in onion. This is corroborated by the findings of Havey (1993).

The correlation between harvest index per plant and plant height, leaf length, leaf diameter was

35

positive and significant, but its association with leaves per plant, bulb dry weight, total soluble solids,

pungency, days to maturity was negative and significant. This implied that economic yield is

associated with germplam lines of early to medium maturity period. This observation was in

conformity with that of Sandhu and Korla (1976).

Days to maturity was correlated positively and significantly with plant height, leaves per plant, leaf

diameter, neck thickness, soluble solids, pungency, fresh and dry weights above ground. This probably

indicated that longer phenological period could result in large biomass accumulation with minimum

contribution to bulb yield due to less efficiency in dry matter partitioning. Similar views were

expressed by Brewster (1990a).

Similarly, fresh and dry weights above ground were positively and significantly correlated with plant

height, leaf length, leaves per plant, leaf diameter, neck thickness and pungency. This indicated that

the above ground biomass exerted a critical influence on dry matter production. Pungency also

correlated positively and significantly with, leaf diameter, neck thickness and leaves per plant,

indicating that it was influenced by these traits. There was also negative and significant correlation of

pungency with bulb dry weight (Table 3) . This signified that germplasm lines having high bulb dry

weight were less pungent than those having low dry weight.

Total Soluble Solids indicated negative and significant correlation with plant height, leaf diameter, leaf

length and neck thickness, but showed positive significant correlation with bulb dry weight and leaves

per plant. This could be attributed to the production of non- structural carbohydrates facilitated by

higher photosynthetic efficiency of above ground biomass, which might have contributed significantly

36

to soluble solids concentration in the bulb. These observations are in conformity with that of Simon

(1995). The positive and significant correlation between soluble solids and bulb dry weight also is

suggestive of the fact that the concentration of reducing sugar may increase with increase in bulb dry

matter content.

Bulb dry weight showed negative and significant correlation with plant height, leaf diameter and neck

thickness, but it showed positive significant association with leaf length. This probably indicated that

dry matter accumulation is highly dependent on efficient partitioning of photosynthetic products.

Similar observations were recorded by Robinson (1971).

Neck thickness was positively and significantly correlated with plant height ,leaf length leaves per

plant and leaf diameter .This perhaps indicated that the production and increment of fleshy edible

layers and compactness of bulb were influenced by these traits. This is corroborated by the findings of

Padda et al., (1973).

Leaf diameter correlated positively and significantly with plant height and le af length indicating that

the increase in these traits resulted in production of greater leaf area which might be of significance in

relation to bulb yield. Similar observations were recorded by Mittal and Srivastava (1965).

The positive association of pairs of characters signified the possibility of correlated response to

selection and it followed that with the increase in one, there is a possibility of increment in the other

and the negative correlations might preclude the simultaneous improvement of those traits along with

each other.

37

4.4. Path Coefficient Analysis

Phenotypic and genotypic corrleations were analyzed further by path-coefficient technique, which

involved partitioning of the correlation coefficients into direct and indirect effects via alternative

characters or pathways. Bulb yield, being the complex outcome of various characters, was considered

to be the resultant variable, and the rest of the variable viz., biological yield per plant, harvest index per

plant, days to maturity, fresh and dry weights above ground, pungency, total soluble solids, bulb dry

weight, neck thickness, leaf diameter, leaves per plant, leaf length and plant height were the causal

variables. It was observed that each of these characters did influence bulb yield directly or indirectly.

Appreciable residual effects obtained may be due to other traits not included in the present study. The

estimates of direct and indirect effects are presented in Table 4 and 5.

4.4.1. Phenotypic Direct and Indirect Effects of Various Characters on

Bulb Yield Per Plant

Biological yield and harvest index per plant contributed their major effects as direct effects (Table 4).

These characters could be considered as main components of selection in a breeding program for

obtaining higher bulb yield and these characters significantly correlated with each other. The other

characters that had positive direct effects included, plant height (0.168), leaf diameter (0.186), neck

thickness (0.0400) and bulb dry weight (0.0137). All these characters were positively associated with

bulb yield except bulb dry weight in which the net effect in the system of opposing influences via

various characters counterbalanced each other making the over all correlation of bulb yield with this

trait as negative (Table 4). These positive direct effects with other characters kept constant indicated

that by increasing one of these characters, there is a possibility to increase bulb yield. In concurrent to

38

the present result, Singh (1981) found positive direct effect of harvest index, biological yield and plant

height in garlic. In the present study, negative direct effects were extended on bulb yield by number

of leaves (-0.0505 ), total soluble solids (-0.1356) , pungency (-0.0523), fresh weight above ground (-

0.10037), dry weight above ground (-0.0914), and days to maturity (-0.0835). The negative direct

effects of fresh and dry weights above ground on bulb yield was observed to be counterbalanced by

the positive indirect influences via plant height , leaf length , leaf diameter, neck thickness and

biological yield per plant and others with low scale values making the over all correlation between

these traits and bulb yield positive. Similar observations were also recorded by Singh (1981) in garlic.

Leaves per plant exhibited unfavorable indirect effects via all the traits except plant height ,neck

thickness and biological yield per plant .Total soluble solids also showed unfavorable direct effects on

most of the characters studied ( Table 4). In spite of its direct positive effect on bulb yield , harvest

index also demonstrated positive indirect effects through all the characters except bulb dry weight and

biological yield per plant. Leaf diameter exerted favorable indirect effect via plant height, neck

thickness, harvest index per plant and biological yield per plant . The negative correlation of leaves per

plant with bulb yield recorded was mainly due to the sum total of its unfavorable indirect effects via

the characters like fresh and dry weights above ground, days to maturity and harvest index per plant.

Leaves per plant, however, exerted substantial positive indirect effect via biological yield per plant

(Table 4).

The positive direct effect of plant height on bulb yield was counterbalanced by the negative indirect

effect via leaf length . However, other unfavorable indirect effects were outweighed by the favorable

39

indirect effects causing a positive correlation of plant height with bulb yield. The indirect effects of

bulb dry weight on bulb yield was also unfavorable (Table 4) . Similarly pungency also showed

unfavorable indirect effect on bulb yield. Neck thickness demonstrated favorable direct effect on bulb

yield per plant via plant height, leaf diameter, harvest index per plant and biological yield per plant.

In spite of negative direct effect of fresh weight above ground on bulb yield, its positive association

with bulb yield was derived mainly through considerable positive indirect effects via plant height, leaf

length, leaf diameter , neck thickness and biological yield per plant . Dry weight above ground,

favorably influenced bulb yield indirectly via plant height, leaf length , leaf diameter, neck thickness,

and biological yield per plant. Similarly, the positive correlation of days to maturity with bulb yield was

mainly due to the positive indirect effects via plant height, leaf length, leaf diameter, neck thickness

and biological yield per plant.

The above evidences highlight that due consideration should be placed on harvest index, biological

yield per plant, plant height, leaf length, leaf diameter, neck thickness, and fresh weight above ground,

while selecting germplasm lines for desirable characters in onion.

40

4.4.2. Genotypic Direct and Indirect Effects of Various Characters on Bulb Yield Per Plant.

The path coefficient analysis revealed that dry weight above ground had maximum positive direct

effect ( 3.831 ) followed by leaf diameter ( 1.503 ), plant height (0.538), harvest index per plant

(0.5363), leaves per plant ( 0.443 ) and biological yield per plant (0.4367) (Table 5). Therefore, these

characters are good contributors to bulb yield . This result is in agreement with the findings of Kalloo

et al., (1982 ).

The path coefficient analysis indicated that the various characters influenced the bulb yield favorably

or unfavorably via other characters. Although plant height exerted positive direct effect on bulb yield,

its influence was favorable via leaf length, leaves per plant, bulb dry weight, soluble solids and dry

weight above ground. Similarly leaf length showed favorable indirect effect on bulb yield via plant

height, leaves per plant, leaf diameter, soluble solids and dry weight above ground. Favorable indirect

effect was observed for leaves per plant on bulb yield via plant height, leaf length, dry weight above

ground and harvest index per plant, but it was nullified by the negative indirect effects via neck

thickness, soluble solids, fresh weight above ground and biological yield per plant. Leaf diameter

besides exerting maximum positive direct effect on bulb yield, also showed favorable indirect

influence on bulb yield via plant height, bulb dry weight, soluble solids and dry weight above ground.

Similarly harvest index had positive direct effect on bulb yield and it also had favorable indirect

influence on bulb yield via plant height, leaf diameter, bulb dry weight, soluble solids, pungency, fresh

weight above ground and days to maturity. Majority of the characters studied had high positive

indirect influence between bulb yield and harvest index. Biological yield per plant had positive

direct effect on bulb yield and exerted favorable indirect influence via plant height, leaves per plant

41

,leaf diameter and dry weight above ground.

In spite of its negative direct effect on bulb yield, neck thickness had positive indirect influence on plant

height, leaves per plant, leaf diameter, bulb dry weight, soluble solids and dry weight above ground.

Though its direct effects were negative, bulb dry weight had favorable influence on bulb yie ld via

leaves per plant, neck thickness, pungency , fresh weight above ground and harvest index per plant

.This trait also indicated good favorable indirect influence on pungency. Total Soluble solids had

favorable indirect influence on bulb yield via number of leaves per plant, neck thickness, pungency,

dry weight above ground and harvest index, but its direct effect was negative. Despite its negative

direct effect on bulb yield, pungency displayed

positive indirect effect via plant height, leaves per plant. Leaf diameter ,bulb dry weight, soluble solids,

dry weight above ground and harvest index per plant.

In spite of its negative direct effect on bulb yield, fresh weight above ground showed favorable indirect

positive influence via plant height, le aves per plant ,leaf diameter, bulb dry weight, dry weight above

ground and harvest index. Similarly, dry weight above ground had high direct positive effect on bulb

yield. It also revealed a favorable influence via plant height, leaf diameter, bulb dry weight, dry weight

above ground and harvest index. Days to maturity showed negative direct effect on bulb yield, but the

positive favorable influence was observed between days to maturity and bulb yield via plant height,

leaves per plant, leaf diameter, dry weight above ground and harvest index.

Generally, in addition to the favorable direct effect on bulb yield per plant, majority of the characters

influenced bulb yield positively through harvest index per plant. On the contrary, rest of the characters

42

exerted negligible influence on bulb yield via leaf length . Presence of positive residual effects both at

phenotypic as well as genotypic levels (Table 4 and 5) indicated that some more traits other than the

ones studied might be contributing towards bulb yield.

43

44

5. SUMMARY AND CONCLUSION

Understanding of the magnitude of variability present in crop plants and the degree of association

between different agronomic characters is of utmost importance as it provided the basis for effective

selection. To generate such an information 24 exotic onion (Allium cepa L.) germplasm lines and

two released local cultivars were evaluated in a replicated trial at Alemaya University Research

Station (Rare) during year 2000 main crop season.

Analysis of variance indicated that there were highly significant differences among the genotypes for

all the traits. Wide range of genetic variability, high heritability in the broad sense and expected

genetic advance were noted, thus highlighting good scope for improvement through selection.

High estimates of broad sense heritability were recorded for fresh weight above ground, yield per

plant, bulb dry weight , leaf diameter, harvest index per plant, total soluble solids, pungency, dry weight

above ground, plant height, leaves per plant, leaf length and biological yield per plant. High heritability

estimates coupled with high genetic advance as per cent of mean were obtained for fresh weight

above ground, yield per plant, harvest index per plant, biological yield per plant, dry weight above

ground, pungency, soluble solids, bulb dry weight, leaf diameter, leaves per plant, leaf length, and plant

height suggesting that selection for these traits would be quite effective.

Bulb yield per plant was positively and significantly correlated with plant height, leaf length, leaf

diameter, neck thickness, fresh and dry weights above ground, harvest index per plant and biological

yield per plant. In path coefficient analysis at genotypic level, plant height, leaves per plant, leaf

diameter and dry weight above ground exerted positive direct effects while neck thickness, bulb dry

45

weight, soluble solids, pungency, fresh weight above ground, days to maturity, harvest index per plant

and biological yield per plant exerted negative direct effects on bulb yield per plant respectively.

In path coefficient analysis, at phenotypic level, positive direct effects on bulb yield per plant were

exerted by plant height, leaf diameter, bulb dry weight, harvest index per plant and biological yield per

plant while the negative direct effects were exerted by soluble solids, pungency, fresh weight above

ground and dry weight above ground, leaves per plant and days to maturity, respectively.

The present investigation by utilizing some exotic germplasm lines, demonstrated the existence of high

genetic variability for the characters studied. A number of characters in the present study were found

to be positively associated with bulb yield per plant and among themselves. As the present

investigation is based on single location, the results need further confirmation across locations.

46

6. REFERENCES

Allard,R.W. 1960. Principles of Plant Breeding . John Willey and Sons Inc., New York, London.

p.485 Anon .1990. Agro-meteorology group ,Remote Sensing Center Research and Technology Division.

FAO. Rome Italy. Astley , D., Innes, N.L. and Q.P. Van der Meer. 1982. Genetic Resources of Allium spp.

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51

APPENDICES

52

Appendix Table 1. Mean Performance for various characters of onion (Allium cepa L.) germplasm lines. No. Treatment PH LL LP LD NT BD BL BDW TSS PCY FWAG DWAG DTM YPP HIPP BYPP 1. AC2-I 59.60 48.67 10.94 11.52 1.95 8.07 6.57 12.20 12.20 0.064 105.51 12.42 118.33 85 0.035 19.25 2. AC8-I 61.67 50.67 14.20 2.07 2.35 8.92 6.87 13.40 12.33 0.063 167.43 15.58 118.33 103 0.036 36.58 3. AC11-I 62.38 52.0 14.67 2.53 2.74 8.01 5.34 10.56 13.53 0.356 193.68 22.16 125.00 70 0.021 15.80 4. AC383-I 57.93 47.47 22.87 1.74 2.27 8.17 5.81 12.83 13.33 0.198 181.90 17.98 115.00 113 0.037 25.40 5. AC50-I 64.13 52.60 25.20 2.38 2.71 7.84 6.51 10.60 12.13 0.125 188.32 20.00 125.00 112 0.038 17.65 6. AC726(A)-C 74.87 63.53 19.93 3.19 3.28 7.95 7.56 9.20 12.13 0.134 511.98 42.94 125.00 220 0.043 97.30 7. AC727(A)-C 80.07 68.40 22.60 3.00 3.15 8.35 7.39 9.90 9.80 0.099 554.64 45.45 118.33 253 0.046 116.30 8. Yello granex 54.40 45.88 11.00 2.00 1.83 8.08 5.66 11.53 10.93 0.128 112.43 14.15 111.67 113 0.044 14.10 9. Red creole 68.20 58.53 26.4 2.79 2.63 8.62 7.44 9.67 11.73 0.361 559.93 48.94 125.00 168 0.028 57.68 10. Texas grano

502 74.73 65.53 16.67 2.82 2.92 9.09 7.98 5.40 6.23 0.076 251.88 25.92 111.67 300 0.098 129.67

11. Agrifound darh Red

54.93 44.80 22.00 1.73 2.27 8.35 5.77 7.50 11.36 0.123 167.27 15.29 111.67 120 0.053 24.73

12. Arka Niketan 60.27 49.73 14.4 2.17 2.08 8.08 5.83 10.73 10.83 0.056 170.41 17.32 111.67 193 0.066 55.30 13. Regia 68.20 57.4 16.07 3.19 2.57 8.93 7.96 5.96 7.33 0.080 194.41 20.42 105.00 290 0.121 142.70 14. Xp8403 56.33 46.93 12.87 2.28 2.25 8.28 6.74 7.23 10.13 0.159 130.85 14.50 108.33 170 0.080 44.30 15. Super high gold

No1 70.60 62.07 19.27 2.85 3.01 9.18 7.43 3.93 6.20 0.066 264.21 25.82 115.00 200 0.071 60.37

16. Gladiator 80.4 68.4 17.47 3.81 3.48 9.41 7.71 6.03 9.16 0.118 581.51 45.76 125.00 265 0.051 73.40 17. Rouge de Tana 58.27 48.93 16.80 1.98 2.13 8.44 6.61 8.13 8.63 0.088 108.41 11.90 121.67 116 0.059 46.83 18. Cristal PRR 67.53 56.6 16.13 2.68 2.67 9.73 9.31 4.17 7.50 0.102 237.90 20.03 115.00 230 0.097 43.93 19. Kalipaitiya 57.73 47.0 35.53 1.81 2.69 7.02 5.43 11.10 15.00 0.136 472.75 42.68 121.67 73 0.014 10.97 20. Bombey Red 58.53 48.8 26.53 2.06 2.78 6.59 5.22 9.03 11.03 0.102 165.85 17.79 108.33 143 0.055 41.37 21. N53 57.4 49.2 21.73 2.11 2.61 9.01 6.66 7.36 9.76 0.130 170.33 16.71 121.67 120 0.051 26.73 22. White Hawk 71.13 62.2 20.8 2.72 2.77 9.13 7.78 4.43 6.83 0.122 280.38 25.16 115.00 213 0.072 74.07 23. Sebaquena 55.13 43.73 14.73 2.26 3.11 9.29 7.47 5.53 10.06 0.091 217.90 25.43 125.00 100 0.033 38.40 24. Granex 429 76.8 64.2 19.60 3.38 3.30 9.68 9.07 6.10 6.87 0.126 351.15 30.24 121.67 306 0.085 83.67 25. Adama Red 53.0 44.07 20.47 2.09 2.59 8.89 6.74 9.30 11.53 0.103 170.63 17.37 121.67 120 0.046 32.83 26. Melkam

65.53 55.93 22.67 2.36 2.85 7.39 5.55 9.10 9.93 0.186 235.37 23.18 118.33 118 0.038 33.22

LSD 11.28 11.01 7.46 0.68 0.76 2.83 3.54 3.22 2.89 0.28 143.40 14.56 11.47 83 0.002 43.85 PH= Plant Height; LL= Leaf Length; LP= Leaves per Plant; LD= Leaf Diameter; NT= Neck Thickness; BD= Bulb Diameter; BL= Bulb Length; BDW= Bulb Dry Weight; TSS= Total Soluble Solids; PCY= Pungency; FWAG= Fresh Weight Above Ground; DWAG= Dry Weight Above Ground; DTM= Days To Maturity; YPP= Yield Per Plant; HIPP= Harvest Index Per Plant; BYPP= Biological Yield Per Plant.

53

Appendix Table 2. Analysis of variance for RCB design for 16 characters in onion (Allium cepa L.).

Source of Variation

D.F. Plant Height

Leaf Length

Leaves per Plant

Leaf Diameter

Neck Thickness

Bulb Diameter

Bulb Length

Bulb Dry Weight

Total Soluble Solids

Pungency

Fresh Weight Above Ground

Replication 2 168.124 119.547 11.685 1.342 0.373 1.129 3.478 2.166 1.155 0.00013 23030.208 Germplasm Line 25 206.895** 186.423** 91.536** 0.985 0.550 1.821** 3.676** 22.568 16.884 0.003 66707.108 Error 50 25.616 25.363 11.628 0.097 0.122 1.674 2.626 2.164 1.751 0.00034 4300 CV(%) 7.88 9.33 17.68 12.74 13.17 15.26 23.63 17.31 12.91 17.02 25.27

Table 2 Continued

Source of Variation D.F. Dry Weight Above Ground

Days to Maturity

Yield Per Plant

Harvest Index Per Plant

Biological Yield Per Plant

Replication 2 197.553 11.538 0.610 0.000013 113 Germplasm Line 25 382.471** 109.383** 1.613** 0.002 384.27** Error 50 2218.17 27.538 0.147 0.000001 50.109 CV(%) 27.26 4.46 23.06 27.13 21.5

** - Indicates significant differences at 0.01 probability level

iv

Appendix Table 3. Mean value for 12 high yilding entries

S.n. Germplasm lines Yield Per Plant

1 Granex 429 306

2 Texas Grano 300

3 Regia 290

4 Gladiator 265

5 AC 727 (A)-C 253

6 Cristal PRR 230

7 AC726 (A)-C 220

8 White Hawk 210

9 Supper High Gold N0.1 200

10 Arka Niketan 193

11 Xp8403 170

12 Red Creole 168

v

Appendix Table 4. Monthly Mean and Annual Rainfall (mm) for 1991-2000 at Alemaya.

Year Jan. Feb. March April May June July Aug. Sep. Oct. Nov. Dec. Yearly

tot.

1991 Nil 51.7

(7)

136.2

(14)

73.2

(13)

58.6

(15)

20.2

(5)

109.1

(12)

104.7

(16)

120.1

(17)

25

(4)

nil 52

(5)

750.6

1992 3.9(3) 11.1

(3)

18.2

(4)

85.2

(11)

72.1

(10)

68.3

(10)

78.5

(4)

97.6

(12)

107.3

(11)

39.4

(5)

10.4

(4)

4.1

(1)

596.1

1993 60.6

(6)

52.1

(6)

24.1

(1)

126.5

(18)

164.6

(17)

45.8

(4)

59.9

(11)

76.4

(13)

57

(12)

- - - 667.0

1994 - - - - - - - - - - - - -

1995 - - 2)5. 151.5 22.0 20.2 194.3 131.1 129.0 0.0 0.0 6.6 680.9

1996 47.0

(5)

12.4

(5)

32.5

(6)

144.4

(17)

169.4

(5)

81.8

(15)

92.1

(10)

151.2

(16)

147.7

(12)

0.0 32.7 (4) 0.0 911.2

1997 Nil nil 78.1 (9) 125.4 155.9

(17)

59.8

(14)