UNIVERSITI PUTRA MALAYSIA

SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMORA BATATAS AS A GROUNDCOVER SPECIES

NORIAH BT. OTHMAN

FP 1991 6

SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMOEA BATATAS AS A GROUND COVER SPECIES

by

NORIAH BT . OTHMAN

Thesis Submitted in Fulfi lment of the Requirements for the Degree of Master of Agricultural Science in the Faculty of Agriculture,

Universiti Pertanian Malaysi a .

May 1991

Lovingly dedicated to

ABU BAKAR

MOHD. AZIZI

NUR LIYANA

ACKNOWLEDGEMENTS

I wish to express my s incere appreciation and thanks to my

supervisors, Professor Mohd . Zain Hj . Abdul Karim and Dr. Maheran Abd .

Aziz of Department of Agronomy and Horticulture, Universi t i Pertanian

Malaysia for their invaluable advice , guidance and encouragement

throughout the s tudy .

Special thanks to Encik Mohd . Said Saad , Lecturer , Department of

Agronomy and Horticulture, Universiti Pertanian Malaysia , for his kind

as s i s tance in providing some articles useful to the present s tudy . I

also wish to extend many thanks to Puan Sabariah Buang for her patience

in typ ing the manuscript, and to a l l the research and field staff at

V. P . M . who one way or other helped in the succes s of this project .

Las t , but not least , I wish to thank my husband, Abu Bakar, for

his help and encouragement, unders tanding and tolerance throughout the

duration of the s tudy .

i i i

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ................................. . LIST OF TABLES ................................... .

LIST OF FIGURES .................................. .

LIST OF PLATES ................................... . ABSTRACT

ABSTRAK

CHAPTER

1 INTRODUCTION

2 LITERATURE REVIEW ......................... .

Int roduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some Bot anical Aspects of Sweet Potato . . . . . .

Growth Pattern and Devel opment of Sweet Pot ato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maj or Factors Af fecting Growth of Sweet Pot ato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Shade Tolerance . . . . . . . . . . . . . . . . . . . . . .

Chl orophyl l Content and Chl oropl ast Morpho l ogy in Sun and Shade P l ants . . .

Distribut ion o f Dry Matt e r in P lants . .

P l ant Nutrients

Ni t rogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . .

iv

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4

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Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Cal cium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Magnes i urn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3 MORPHOLOGICAL STUDIES OF TWO CULTIVARS OF SWEET POTATO................................ 21

Materia l s and Method . . . . . . . . . . .. . . . . . . . . . . . . . . . 21

P l ant ing Materia l s . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Experimental Design and Layout . . . . . . . . . . . . . 22

Observatio n and Data Col lection . . . . . . . . . . . . 23

Resul ts . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . 24

General Characteris t ics . . . . . . . . . . . . . . . . . . . . . 24

Leaf S hape and S ize . . . . . . . . . . . . . . . . . . . ...... 24

S tem Elongat ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Growth of Thi rd Branch . . . . . . . . . . . . . . . . . . . . . . 32

Growth of Leaves on Main Stem . . . . . . . . . . . . . . 34

The Flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

The Storage Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4 EFFECTS OF SHADING AND FERTILIZER LEVELS ON GROWTH OF THE 'VARIEGATED' CULTIVAR . . . . . • . . 41

Materials and Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Experimental Design and Layout . . . . . . . . . . . . 42

Management P ract ices . . . . . . . . . . . . . . . . . . . . . . 44

Data Col lection . . . . . . . . . . . . . . . . . . . . . ...... 46

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Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Dry Wei ght . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 48

Effect of Shadi ng . . . . . . . . . . . . . . . . . . . . . 48

Effect of Fert i l i zer Leve l s . . . . . . . . . . . 50

Growth of Mai n Stem . . . . . . . . . . . . . . . . . . . . . . . 52

Total Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

LAR and LALW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Chl o rophyl l Content . . . . . . . . . . . . . . . . . . . . . . . 55

Qua l i ty Rat i ng of the P l ants . . . . . . . . . . . . . . 58

Nut r i e nt Content . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Di scuss i o n . . . . . .. . .. . .. .. ... .. . . .. ... .. . . . .. 62

5 EFFECTS OF SHADE ON LIGHT COMPENSATI ON POINT . . . . . . . . . . . . . . . . . . . . . . . , ......... " . . . . 66

Mater i al s and Method . . . . . . . . . . . . . . . . . . . . . . . . 66

Resul ts . . . . . . . . , . . .. . . . . . . . . . . . . . .. . .... . . .. 70

Di scus s i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

6 MINERAL NUTRITION . . . . . . .. . . . . . . . . . . . . . . . .. . 7 7

Mater i a l s and Method . . . . . . . . . . . . . . . . . . . . . . . . 77

S i te of Experiment . . . . . . . . . . . . . . . . . . . . . . 79

Ster i l i z at i on of Equi pment . . . . . . . . . . . . . . 7 9

Nut r i ents i n Solution . . . . . . . . . . . . . . . . . . . . 7 9

Experimental Layout . . . .. . . . . . . . . . . . . .. . . 80

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Management of Nutrient Solution . . . . . . . . . . . . . 8 2

Control o f E l ec t r i cal Conduct iv i ty ( E . C ) . . 82

Cont rol of pH . . .. . . . . . . . . . . . . . . . . . . . . . . . . 8 2

Data Col lect i on . . . • . . . . . . . . . . • • . . . . . . . . . . . . . 8 3

Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Growth o f t he P l ant Organs with Time . . . . • • • . 8 3

Nutrients Content of the P l ants . . . . . . . . . . . . . . 85

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

7 GENERAL D I SCUSSION • . . . • • . . . . . • • • • • . . • • • . . . . . . . . . 92

8 SUMMARY . . . . . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . . . . . . . 9 5

BIBLIOGRAPHY 97

APPENDI CES

A - METEOROLOGI CAL DATA 105

B - DETERM I NAT ION OF CHLOROPHYLL CONTENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

C - DETERMINATION OF MINERAL NUTRI ENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

D - T - TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

E - ANALYS I S OF VARIANCE . . . . . . . . . . . . . . . . . . . . . 120

F - GROWTH RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

v ii

Table

1

2

3

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7

8

9

10

11

12

1 3

LIST O F TABLES

Weekly I ncrements ( em ) of Main Stem of Two Sweet Potato Cul tivars Grown Under Lathhouse Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weekly Increments ( em ) of Third Branch o f Two Sweet Potato Cultivars Grown Under Lathhouse Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Weekly Increments of Leaves of Two Sweet Potato Cul tivars Grown Under Lathhouse Condi tions . . . . . . . . . . . .

Light Intensi ties (mol m-2s-1 ) at Three Different Time at the Beginning of the Experiment ( A ) , and at Harves ting ( B ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence of Di fferent Leve ls of Ferti lizer on the Dry Wei ght of the Plants Grown Under Five Shade Leve l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth of Main Stem ( em ) as Affected by S hades and Ferti l izer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The E ffects of Di fferent Shades and Ferti lizer L evels on LAR , LALW , Qual ity Ratings and Chlorophyll Content of the ' variegated' Cul tivar . . . . . . . . . . . . . . . . . .

Chlorophyl l Content. of Leaves ( mg/cm2 x 10-3) as Affected by Shades and Ferti l izer Level s . . . . . . . . . . . . . .

Influence of Di fferent Rates of Fert i l izer on Percentage of N, P , K , Ca and Mg Content Under Five Shade Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Content of Elements ( % ) Based on Dry Wei ght of Leaves at Di fferent Shades and Fertilizer Level s . . . . . . Light Compensation Point ( umol m2s-1 ) of Two Sweet Potato Cul tivars Under Di fferent Shades Level . . . . . . . . . Light Saturation Point ( umol m2s-1 ) of Two Sweet Potato Grown Under Di fferent Level of Shades . . . . . . . . . . Content of E l ements ( % ) at the E nd of F ive Weeks Growth in Control led Nutrient Solution . . . . . . : . . . . . . . .

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Table Page

1 4 Amount of Nutrient s (%jg) Removed at F ive Weeks Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 5 Amount of Nutrients ( %/g ) Removed b y cv. ' variegated ' P lanted in the Soil at the Age o f Twelve Weeks . . . . . . . 91

ix

LIST OF FIGURES

Figure

1 The Hypothetical Respons e of Photosynthesis t o Light I ntens ity and CO2 Concentration . . . . . . . . . . . . . . . .

2 Length of Main Stem of Two Sweet Potato Cult ivars Under Lathhouse Condit ions . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Length of Third Branch of Two Sweet Potato Cultivars Under Lathhouse Conditions . . . . . . . . . . . . . . . .

4 Number o f Leaves of the Main S t em Under Lathhouse

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33

Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

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1 1

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Diagram of the Factorial Experiment in Sp l it P l ot Des ign in Experiment 2 .............................. .

Diagram of the Shade House and the Posit ion of the Wooden Box . Each Shade House is Ful l y Cov ered with Sarlon Mesh of Dif f e rent Shade L ev el s . . . . . . . . . . . . . . . . I nf luence of Dif f erent Shade L evel s on t he Total Dry Weight of the P l ants Grown Under Four Fert il izer Leve l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I nf l uence of Dif f e rent Levels o f Fertil iz er o n the Total Dry Weight of the P l ants Grown Under Five Shade Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth of the Main S t em ( cm) as Aff ect ed by Shades and Ferti l iz e r Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total Leaf Area of 'variegated ' Cul t ivar Subjected to Diff erent Shading and Rates o f Fertil iz er Treatment at the End o f Three Month's Growt h . . . . . . . . .

Chl orophyl l Cont e nt of ' variegated ' L eave s Subj ect ed to Dif f e rent Shading and Rat e of Fertil iz er Treatments at the End of Three Month ' s Growth . . . . . . . .

Parkinson Leaf Chamber {ADC ) . . . . . . . . . . . . . . . . . . . . . . . . . Diagrammat ic S et-up of the Equipment . . . . . . . . . . . . . . . . .

Light Compensation Point of Two Sweet Potato Cul t ivars Under Dif f erent Shading Treatment s at the End of One Month's Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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69

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Figure

1 5

1 6

1 7

1 8

1 9

20

2 1

Regression o f Light Compensation Point on Shades in Two Cult ivars of Sweet Potato . . . . . . . . . . . . . . . . . . . . . . . . . Ligh t Saturation Curves for Both Cultivars Grown Under Different Levels of Shade . . . . . . . . . . . . . . . . . . . . . . . Hydroponic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of Two Sweet Potato Cul tivars P lanted in Completely Randomized Block Design Under Hydroponic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry Weight Accumulation of Two Sweet Potato Cultivars Grown in Contro lled Nutrient Solution

Nutrient Content of Leaves , Stem and Root s of Two Sweet Potato Cul tivars Grown in Controlled Nutrient Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of the Comp lete Module Used to Determine Nitrogen in Kj eldahl Digests by the Autoanalyser Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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III

LIST OF PLATES

Plate Page

1 The Two Sweet Potato Cultivars . . . . . . . . . . . . . . . . . . . . . . . . 25

2 The Branching Pattern of Both Cul tivars . . . . . . . . . . . . . . 26

3 Adaxial View of the ' variegated ' Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7

4 Abaxia l View of the ' variegated ' Leaves . . . . . . . . . . . . . 2 7

5 Adaxial View of the Leaves of cv . Imelda . . . . . . . . . . . . . . 29

6 Abaxial View of the Leaves of cv . Imelda ... . . . . . . . . . . . 29

7 The Flowers of cv . Imelda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

8 Closer View of the Flower of cv . Imelda . . . . . . . . . . . , . . . 36

9 The S torage Roots of the Two Sweet Potato Cul tivars . . . 3 8

xii

Abs tract o f the thesi s presented to the Senate o f Universi t i Pertanian Mal aysia in fulfillment of the requirements for the degree of Master of Agricultural Science .

SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMOEA BATATAS AS A GROUND COVER SPECIES

by

Noriah Binti Othman

May 1 9 9 1

Supervisor Professor Mohd . Zain Haj i Abdul Karim

Facul ty Agricul ture

The morphological development and some physiological aspects were

s tudied on two cultivars of sweet potato whi ch are normally used as an

ornamenta l plant . Among the s tudies undertaken were those on the

botanical characteristics of the plants , effects of shade and

fertilizer and nutrient uptake . The cul tivar examined were Imelda and

an unnamed ' variegated ' type.

The effects of shading and fertilizer l eve l s showed growth of the

t variegated ' cul t i var were severely reduced in heavy shading (70% and

80%) . Increasing s hade level s i ncreased leaf area ratio ( LAR) and

leaf area to leaf weight ( LALW ) , but decreased dry matter production ,

visible quality , chlorophyll content and elemental composi tion in the

leaf tissue . However , ferti lizer levels were less effective than shade

in altering the parameters above. As shade l evel s increased , the

content of nitrogen , phosphorus , potas sium , calcium and magnesium in

xi i i

the l eaves increased . Shade levels signi fi cantly affected l i ght

compensation point (Lep) in both cul tivars . Increasing shade levels

decreased LCP . LCP of cv. ' variegated ' is lower than cv . Imelda ,

suggesting that cv . ' variegated ' i s more adaptable to a moderate shade .

S tudies on the nutrient uptake of both cul tivars using hydroponic

techniques showed that the highest element in the leaves , s tem and root

was potassium and fol lowed in descending order by nitrogen , calcium ,

phosphorus and magnesium . However , instead o f calcium , phosphorus was

higher in the root .

In general , both cultivars are suitable as groundcove r p l ants

with the 'variegated' cultivar more adaptab l e to shade than cv . Imelda .

xiv

Abstrak tesis yang dikemukakan kepada S enat Universiti Pertanian Malaysia sebagai memenuhi syarat untuk rj azah Master Sains Pertanian .

BBBBRAPA KAJIAN FISIOLOGI IB ATAS IPOMOEA BATATAS SRBAGAI SPESIBS TANAMAN HIASAN PRNUTUP BUMI

oleh

Noriah Binti Othman

Mei 1991

Penyel i a Profes'sor Mohd . Zain Haj i Abdul Karim

Fakulti Pertanian

P erkembangan morfologikal dan beberapa aspek fisiologikal telah

dikaj i ke atas dua kultivar ubi keledek yang biasanya digunakan s ebagai

tanaman hiasan . Kaj ian ini tertumpu pada ciri-ciri botanikal tanaman

ini , kesan baj a dan cahaya serta pengambi lan nutrien . Kultivar yang

dikaj i ialah Imelda dan j enis warna-warni yang tidak bernama.

Has i 1 kaj ian kesan teduhan dan baj a menunj ukkan pertumbuhan

kul t ivar yang berwarna-warni kel ihatan jelas terencat di bawah teduhan

yang tinggi ( 70% dan 80%) . Peningkatan paras teduhan telah menambahkan

kadar keluasan daun ( LAR ) dan kadar luas daU1\ p er berat daun (LALW),

tetap i mengurangkan penghasilan berat kering , kual i t i tanaman

dilihat dari sudut mata kasar , kandungan klorofil dan kompos i s i

elemen di dalam tisu daun . Namun demiki an , paras baja kurang memberi

kesan berbanding dengan teduhan di dalam mengubah parameter-parameter

di atas . Apabi l a paras baj a bertambah , kandungan nitrogen , posforus ,

xv

kalium , kalsium dan magnesium di dalam daun j uga turut bertambah . Paras

teduhan memberi kesan yang bererti pada tahap tepu cahaya ( LCP ) pada

kedua-dua kul tivar . Meninggikan paras teduhan menyebabkan tahap tepu

cahaya menurun . Kultivar berwarna-warni mempunyai LCP yang lebih rendah

dari kul tivar Imelda , mencadangkan kultivar berwarna-warni ini l ebih

dapat mengadaptasi pada keadaan teduhan yang s ederhana .

Kaj ian mengenai pengambilan nutrien pada kedua-dua kul tivar

menggunakan teknik hidroponik menunj ukkan elemen yang tertinggi di

dalam daun , batang dan akar ia lah kalium diikuti dalam susunan menurun

nitrogen , kals ium , posforus dan magnesium . Sungguhpun demikian ,

bukannya kal sium tetapi posforus lebih tinggi di dalam akar .

Amnya , kedua-dua kul tivar adalah sesuai sebagai tanaman penutup

bumi dan kul tivar yang berwarna-warni lebih dapat mengadaptas ikan diri

daripada kultivar Imelda .

CHAPTER 1

INTRODUCTION

The deve lopment o f the sweet potato ( Ipomoea batatas ) as a food

crop is as old as civi lization itsel f . Its ances tral home i s Tropical

America , in Central America or North Western South America ( Brand ,

1 9 7 1 ) . The species was an important food crop of the Mayans in Central

America and of the P eruvians in the Andes . Both civil izations

developed an advanced type of agriculture . Although maize was the

maj or crop , the natives also grew sweet potatoes . In fact by the time

of the discovery of America , they had extended the culture of thi s

important crop to Mexico , the Wes t Indies and certain parts of South

America ( Brand 1 9 7 1 ) .

Many records show that Spanish exp lorers of the early part of the

sixteenth century carried the plant , presumably by means of the fleshy

roots , in both the eas terly and wes terly directions , to Spain , Africa

and the Far Eas t ( Horne1 , 1 9 4 5 ) .

The pres ent day sweet potato w�s developed through centuries o f

culture in which a large number of cu1 tivars have risen through natural

hybridization and selection , mutations as well as through systematic

breeding efforts ( Purseglove , 1 9 6 8 ) .

One of the advantages of sweet potato compared to other tuber

crops , e . g . , tapioca , is that it is more drought tolerant ( Culwick ,

1

2

1 9 4 1 ) . Furthermore , the crop is considered useful as a famine reserve

( Brooke , 1 9 7 2 ) . Sweet potato has the advantage of being a good cover

crop , minimizing soil erosion and suppresses weed growth as wel l as

providing addi tional income from the tubers . The protective cover

provided by its vines reduces the e ros ivi ty of raindrops and run off ,

and competes we l l with weeds .

So far , s tudies on sweet potato have been emphas ized on the tuber

production and as food crop ( Lantican and Soriano , 1 9 6 1; B i swas and

Bos e , 1 9 80; Bartolini , 1 983) . Recentl y , two cul tivars of sweet potato

were introduced to Malays ia and were p l anted as ornamental groundcover

along the roadsides and under trees . One cul tivar is characterised by

large yel lowi sh green leaves believed to be originated from the

Phi lippines . The cultivar is known as Ime lda . It i s used as borders

of yield tests becaus e of i ts distinct colour at Phi l ippine Root Crop

Research & Training Center ( PRCRTC ) . However , i t is low yie lding and

is susceptible to attack by weevi l s ( Cylas formicarius ) . A second

cultivar is a ' variegated ' typ e with the l eaves having two different

co lours , i . e . dark green and purp li sh . It i s s aid to be originated

from Hawaii . Unfortunately the name of this cul tivar is s ti l l unknown .

The attractive colour of the leaves is the main reason that triggered

the interes t of some horti culturists to cul tivate them as ornamental

plants either as individual s or in combination with other ornamental

p lants to emphasiz e the colour and to give an appea ling look to

onlookers . Because there i s l ittle information on the two cul tivars ,

especi a l ly on the morphological and physiological behaviour under

3

Malaysian conditions, i t is essential that certain aspects of their

phys iology be studied . I t is hoped that these s tudies will help to

assess the potential of the cul tivars as ornamental groundcover .

Effects of varied light intensities on the growth of the p l ants ,

and mineral requirements for the growth and development o f the

cultivars are important phys iological aspects that wi l l contribute

towards our understanding of the physiological behaviour of the two

cultivars thus enabling us to provide the appropriate environment for

their growth . The s tudies reported here examine the aspects mentioned

above . With a better understanding o f the characterist i cs of these

two cultivars , i t is hoped that they can be grown as ornamentals under

appropriate conditions and es tabli sh as important groundcover plants in

Malaysia .

The specific objectives of the inves tigation reported in thi s

the s i s are:

1 . To s tudy the morpho logical development o f the two

cul tivars under lathhouse conditions ( Experiment 1 ) .

2 . To study the e ffects o f shading and different rates o f

fertil izer on the growth , nutrient composition and qua l i ty

of the 'vari egated ' cul tivar ( Experiment 2 ) .

3 . To determine the l i ght compensation point o f the two

cul tivars at varying degrees o f shading ( Experiment 3 ) .

4 . To s tudy the mineral requirement of the two cultivars

( Experiment 4 ) .

CHAPTER 2

LITERATURE REVIEW

Introduc t i on

Very l i t t l e s tud ies have been made on Ipomoea batat as f r om the

point of view of the use of the species f or ornament al purposes . The

review of l i terature therefore wi l l consi de r phys i ol ogical s tudies on

the spec i es as a whol e par t i cu l arly those aspects that re l at e to the

present i nves t igat i ons .

S ome Bot an i ca l Aspects of Sweet Potato

The sweet potato bel ongs t o the f ami ly Convolvul aceae , a group

whi ch c omprises about 50 genera, 1 20 0 or more species ( Pursegl ove ,

1 9 6 8 ) . The p l ant i s a twining perenn i a l herb but t reated as an annual

in cul t i vat i on . The p lants i n thi s fami l y have d i s t i ngui shing

characterist i cs : l atex i s present in the i r sap , the stems are erect,

t rai l i ng or cl imbing according t o the species , and contain b i c oll ateral

vascul ar bundles. Advent i t i ous roots are progress ive ly at the nodes

and i n thi s manner the p l ants creep a l ong ( Purseg l ove , 1 9 68) . The

f l owers are compl ete with a super i or p i st i l , f ive stamens , and a

trumpet shaped corol l a . The f ru i t i s a capsul e and the seed contains

an embryo with f olded cotyl edons ( Pursegl ove , 1 968 ) .

The major part of the t op system of the stem consi st s of primary

l ateral s . Varietal d i f f erences and simi l ar i t i es occured in l ength of

4

the main axis and

(Pursegl ove , 1 9 68).

5

in number of primary and secondary l aterals

The leaf system in the sweet potato deve lops a

re l at i vel y l arge number of simpl e , moderate l y l arge- bladed , l ong

pet iol ated leaf ( Purseg l ove , 1 9 68 ) . Hayward (1938) s t ated the first

l eaves were cordate whil e those formed l ater may be hastate , cut or

l obed. Thus the l eaf shade varies with the age of the pl ant.

The tubers are the f l eshy enl argement of cert ain of the l arger

roots and deve l op in the f irst 2 2 .5 cm of the soil . They are either

bunched together or borne on l ateral s , varying in length f rom several

cent imeter to 30 cm . The shape of the tubers cou l d vary considerabl y

even in the same variety depending on soil or other environmental

f actors (Pursegl ove , 1 9 6 8).

Growth Pattern and Development of Sweet Potato

Miltho rpe ( 1 967) and Mi l thorpe and Moorby ( 1 9 74 ) have described

the growth pattern of root crops ( with particul ar references to t he

pot at o , sugar beet and sweet potat o) as roughly consis t ing of three

vegetat ive phases . The phases comprise a pre-emergence or estab l ishment

phas e , a canopy deve l opment phase and the st orage or bul king phase .

Sweet pot at o may al so exhibit an initial l ag phase in which no

tubers are formed unt il a cert ain amount of l eaf growth has taken place

( Mil t horpe , 1 9 67). I n yet another pattern of growth there is

simu l t aneous shoot and tuber growth without the requirement f or an

6

ini t i al canopy development phase ( Lowe and Wi l son, 1 9 7 4 ) . There are

contras t i ng opinions as to the importance of l eaf area in the sweet

potat o . It has been shown that st aking the pl ants improves l eaf

d i s pl ay and increases Leaf Area Index ( LAI ) with the f i nal resu l t of

incre ased yields ( Chapman and Cowl ing , 1 9 6 5 ) . Haynes et al . , ( 1 9 6 7 )

beli eved in the exi s tence of an opt imal LAI . Lowe and Wil son (1 974 ) ,

on the other hand were of the opinion that the sink e f fect o f the

devel oping tubers was more cruci al in determi ning yield rather than

fol i age characteris t i cs . Nevertheless , t he i r work , showing that ear l y

v i go rous shoot growth delayed tube r bulking in gene ral and leading t o

lowered part i t i oning o f total dry matter to the tubers , seems to be

consi s tent with the concept of an opt imal LAI for economi c yi e l d .

Major Factors Affecting Growth of _Sweet Potato

Light

Growth of autotrophic pl ants is inf l uenced by the intenSity of

l i ght . Plants occupying sunny habi tats ( sun plants ) are general l y

capab l e of hi gher photosynthetic rates at high quantum f l ux densit i es

(l i ght intens i ty ) than pl ants restr i cted t oshaded locat ions ( shade

pl ant s ) ( Gabri e l sen , 1 9 6 0 ) .

At l ow quantum f l ux dens i t ies , photosyntheSis is l inearl y

dependent on quantum f l ux dens i ty and the e f f iciency of l ight as shown

in f i gure 1 ( Bjorkman , 1 9 8 1 ) . At higher quantum f lux densities, the

Respira tlOn PhotosynthesIs

-z -1 (umol CO2 m s )

/

/' / //

// / /

- - -/- - - - - - - - -- - - - - ---V

-------------

o ,1 .... /

LIght CompensatlOn

Pomt

Saturatmg LIght IntensIty

LIGHT INTENSITY

-2 -1 (UE m s )

HIgh CO 2

�ledlUm CO z

Low CO2

FIgure 1. The Hypothetical Response of PhotosynthesIS

to LIght IntensIty and C02 ConcentratlOn

"­'-, 7

.....

8

increase in photosynthes i s i s less than proportional to the increase in

quantum flux dens ities ( partial light saturation ) and u ltimately ,

photosynthes i s fai l s to increase wi th increasing light intensi ty ( light

saturation ) ( Bj orkman , 1 9 8 1 ) .

Reduced light intens ity may a l s o s t imulate compensatory growth or

movement , including new chlorophyll producti on , epinasty and leaf

expansi on . In contras t , changes i n photop eriodism or in l ight-induced

germination are often controlled by very low light intensities and

brief exposure ( Bickford and Dunn , 1 9 7 2 ) .

The l i ght intensi ty at whi ch photosynthesis j us t balances

respiration ( net carbon dioxide exchange is zero ) is called the l ight

compensation point ( Salisbury and Ros s , 1 9 7 8 ) . This point varies wi th

the speci es , with the light intensi ty during growth ( Conover and Pool e ,

1 97 5 ) and to some extent wi th the temperature a t which measurements are

made and carbon dioxide concentrat i on ( Salisbury and Ross , 1 9 78 ) .

Species with a s teep photosynthet i c curve would be expected to show an

unfavourab le photosyntheti c balance when subjected to changed light o r

temperature whi l e those wi th sha l l ow curve would be expected t o b e

little a ffected by the environment ( Banni ster , 1 9 76 ) .

At atmospheric concentrations o f carbon di oxide , the values of the

light compensation point are s trongly influenced by temperature; this

effect may be very marked at high temperatures ann even at lower