The Reduced Height Genes Do Not Affect the Root Penetration Ability in Wheat

8/14/2019 The Reduced Height Genes Do Not Affect the Root Penetration Ability in Wheat

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Euphytica (2005) 141: 105111

DOI: 10.1007/s10681-005-6161-4 C Springer 2005

The reduced height genes do not affect the root penetration ability in wheat

K. Kubo1, Y. Jitsuyama1, K. Iwama1, N. Watanabe2, A. Yanagisawa3, I. Elouafi4 & M.M. Nachit41 Department of Botany and Agronomy, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan;2 Department of Plant Genetics and Production, Faculty of Applied Biological Science, Gifu University, Gifu,

Japan; 3Hokkaido Prefectural Kitami Agricultural Experiment Station, Tokoro, Japan; 4 International Center

for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria; (author for correspondence: e-mail:

[email protected])

Received 22 April 2004; accepted 11 November 2004

Key words: drought avoidance, genetic control mechanism, reduced height genes, root penetration, soil compaction,wheat

Summary

Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum

(Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water

deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b

orRht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the

Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of LD222 durum wheat

and April Bearded bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross

between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b).

One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thicknessmade from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP

index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots

per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In

NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b orRht-D1b dwarfing

genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were

higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant

(r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We

suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.

Abbreviations: DW: dry weight, NILs: near-isogenic lines, GA: gibberellin, PV: the mixture of paraffin and Vaseline,

RILs: recombinant inbred lines, PVRN: the number of roots penetrating through the PV disc per plant, RP: root

penetration, TRN: total number of seminal and crown roots per plant, WANA: West Asia and North Africa

Introduction

Water shortage is one of the most serious constraints

on increasing wheat yields in West Asian and North

African (WANA) region because of low precipita-

tion and lack of irrigation systems (Rajaram et al.,

1996; Nachit, 1998). Although water acquisition from

deep soils is beneficial for plants to avoid drought

(Loomis & Connor, 1992), the roots sometimes can-

not extend to deep soils because of a compacted

soil layer, especially in a drought condition (Unger

& Kaspar, 1994). In fact, subsurface compaction

restricts root extension and decreases grain yields

of wheat in Morocco (Oussible et al., 1992). For

stable crop production in WANA region, increas-

ing root penetration (RP) ability in compacted soils

should be considered as one of the important breeding

targets.


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Since the Green Revolution, semi-dwarf geno-

types with Rht-B1b orRht-D1b gene have contributed

to increasethe yield of wheat in favourableand irrigatedconditions (Gale & Youssefian, 1985).Rht-B1b orRht-

D1b gene has major gene effect to decrease shoot

length by reduction of cell length of internodes, fol-

lowed by increasing the harvest index (Miralles et al.,

1998). In addition, some quantitative trait loci (QTLs)

controlling plantheight were recently detected in wheat

(Rebetzke et al., 2001). However, it was reported that

wheat yield shows more year-to-year variation, due to

edaphic condition, in areas cultivating improved geno-

types with Rht genes (Rht-B1b Rht-B1b Rht-D1a Rht-

D1a or Rht-B1a Rht-B1a Rht-D1b Rht-D1b) from the

bread wheat cultivar Norin 10 compared with those

in the areas cultivating prominently conventional geno-

types (Rht-B1a Rht-B1a Rht-D1a Rht-D1a) (Michaels,

1982), especially in WANA region (Srivastava, 1987).

Singh et al. (2001) also showed that the grain yields for

semi-dwarf isolines of durum and bread wheat were

similar to those of tall genotypes under drought con-

ditions, although semi-dwarf isolines had more grain

yields than tall genotypes under favourable conditions.

In our previous study (Kubo et al., 2004), geno-

typic difference of RP ability was shown among du-

rum wheat genotypes, which included seven Ethiopian

landracesand 17 North American cultivars,by themea-

surement with thepot installedPV discs.The numberofroots penetrating through the PV disc, which indicates

RP ability, was significantly larger in Ethiopian lan-

draces than in North American cultivars. It is thought

that Ethiopian landraces have no GA-insensitive re-

duced height (Rht) genes (Rht-B1a Rht-B1a), whereas

semi-dwarf North American cultivars have Rht gene

(Rht-B1b Rht-B1b). The result suggests that the RP

ability of wheat may be negatively affected by Rht

genes. If it is true, it issupposed to bedifficult to breed a

semi-dwarf wheat cultivarof high yieldcombiningwith

a high RP ability. In rice, however, some quantitative

trait loci (QTLs) analyses revealed that QTLs related toRP ability were detected at the different region from the

locus ofsd1 dwarf gene (Ray et al., 1996; Price et al.,

2000; Zheng et al., 2000; Zhang et al., 2001). The re-

sults suggest that the development of the semi-dwarf

cultivars with excellent RP ability will be possible. The

genetic regions and nature of inheritance of RP ability,

including the effects of Rht genes on RP ability, have

not been studied in wheat.

In this study, we investigated a relationship between

RP ability and semi-dwarfness with the near-isogenic

lines (NILs) of Rht gene(s) and recombinant inbred

lines (RILs) in wheat. The NIL of durum wheat cultivar

LD222 has Rht-B1b gene from semi-dwarf cultivar

Cando (Watanabe et al., 2003). Thetwo NILs of breadwheat cultivar April Bearded have either Rht-B1b or

Rht-D1b genes from Norin 10 (Gale & Youssefian,

1985). The RILs were derived from the cross between

tall landrace Jennah Khetifa (Rht-B1a Rht-B1a)anda

semi-dwarf cultivar Cham1 (Rht-B1b Rht-B1b)ofdu-

rum wheat. Jennah Khetifa is a local genotype collected

in 1990 on the southeast plateau of the Atlas Moun-

tains of Morocco (Nachit et al., 2001), dominating Xe-

rosols (FAO-UNESCO, 1978). This genotype specially

adapts to the North African continental dryland and

is moderately resistant to drought and cold. Cham1

(Pelicano/Ruff//Gaviota/Rolette), grown in several

countries of the Mediterranean region, is a commer-

cial cultivar bred by the International Center for Agri-

cultural Research in Dry Areas (ICARDA). This semi-

dwarf cultivar is carriedRht-B1b gene from Norin 10,

andhas a high yield potentialand yield stability (Nachit

et al., 2001). It also has a good drought tolerance be-

cause of a high ability of osmotic adjustment (Rekika et

al., 1998). The RP ability was evaluated using the sim-

ilar pots installed PV disc described by the previous

study (Kubo et al., 2004)

Materials and methods

The study was done from June 11th to August 16th,

2002, under a polyhouse at the Field Science Cen-

ter for the Northern Biosphere, Hokkaido University

(Sapporo, Japan, 43N, 141E). The air temperature

during the experiment was 1325 C. One NIL of du-

rum wheat cultivar LD222, two NILs of bread wheat

April Bearded and both recurrent parents, and the 110

RILs of durum wheat derived from a cross between

Jennah Khetifa and Cham1 were used.

The pot used to evaluate RP ability consisted of a

10 cm tall polyvinyl chloride tube above another 5 cm

tall tube (Figure 1). A disc (0.3 cm thickness, 6 cmdiameter) made from a mixture of 400 g kg1 paraf-

fin and 600 g kg1 Vaseline (PV) was placed between

the two tubes as a substitute for compacted soil layer,

that were then fixed at the joint. The bottom of the

pot was covered with a non-woven fabric. The tubes

were filled with non-compacted vermiculite, with 60,

100, 50 and 30 g m3 of N, P2O5, K2O and MgO, re-

spectively. The experimental design was a randomized

complete block with six replications for LD222, April

Bearded and their NILs, and with three replications

for Jennah Khetifa, Cham1 and their RILs. The pots


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Figure 1. Diagram of the pot used in the experiment. Each pot

was made from polyvinyl chloride tubes, and had inside a PV disc

(mixture of 400 g kg1 paraffin and 600 g kg1 Vaseline).

were arranged on a tray (1350 550 150 mm), and

covered with a silver sheet. Three seeds of each mate-

rial were sown 1 cm deep in a pot, and the plants were

thinned to one seedling in a pot at 10 days after sowing.

The vermiculite below the PV disc in the pot was kept

water-saturated by keeping the water level in the trays

1 cm depth during the experiment. The water content

of the vermiculite above the PV disc in each pot was

measured by using an FDR soil moisture meter (DIK-311A, Daiki Rica Kogyo Co., Ltd., Tokyo, Japan), and

was adjusted to 50% in volume by irrigation when it

decreased to 20%.

Since the hardness of the PV disc changed with its

temperature, the hardness of the PV disc was estimated

by using the regression formula of the relationship be-

tween thetemperatureand thehardnessin PV mixtures,

Y= 0.360 Loge(X)+ 1.533,

where Y is the hardness of the PV disc and X is the

temperature of the PV disc (Kubo et al., 2004). At eightweeks after sowing (approximately the heading stage

of the seedlings), the shoot length, number of stems

and number of leaves on the main stem were recorded.

Then the non-woven fabric and tubes were removed

carefully. After washing away the vermiculite from the

roots, the number of roots penetrating through the PV

disc per plant (PVRN) and the total number of seminal

and crown roots per plant (TRN) were counted. Then

the roots above the PV disc were sampled to measure

the dry weight (DW). The shoot DW and root DW were

recorded after oven-drying at 80 C for 48 h. The RP

index was calculated as the proportion of PVRN to

TRN (Yu et al., 1995). Statistical analyses were done

by using the software SPSS (Ver.7.5.1J, SPSS Japan,Tokyo, Japan).

Results

Hardness of the PV disc

Because the temperature of the PV disc increased from

15to26 C, the hardness of the PV disc decreased from

0.57 to 0.36 MPa, during the experiment.

Experiment for the NILs

In comparisons between LD222 and its NIL with Rht-

B1b gene, and between April Bearded and its NILs

with eithertheRht-B1b orRht-D1b gene, tall genotypes

(LD222 and April Bearded) always had a higher shoot

length than their NILs (Table 1). However, the PVRN

was not significantly different from both near-isogenic

pairs. There were no significant differences in TRNand

RP index between NIL(s) and recurrent parent for both

genetic backgrounds.

Experiment for the RILs

Shoot length, PVRN, TRN and RP index of RILs and

their parents were shown in Table 2. Jennah Khetifa

had much longer shoot length than Cham1. Jennah

Khetifa also had more than two times greater PVRN

than Cham1, and the RILs had high coefficient of vari-

ation (CV) in this trait. The difference between the

parents was small in TRN, while was relatively large

in RP index, although there was no statistical signifi-

cance in both traits. The CV in the RILs was also much

higher for the RP index than for TRN. PVRN had a

significant positive correlation with both TRN and RP

index among RILs (Table 3). The correlation coeffi-cient was, however, much higher for the relationship

between PVRN and RP index. The correlation coeffi-

cient between RP index and TRN was around nil.

The TRN had significant correlations with number

of stems (r = 0.665, P < 0.01), number of leaves

on the main stem (r = 0.447, P < 0.01), shoot DW

(r = 0.523, P < 0.01) and root DW above the PV

disc (r = 0.587, P < 0.01) among the RILs. However,

the RP index did not have significant correlations with

all the traits except for shoot DW (r = 0.223, 0.01

P < 0.05).


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Table 1. Shoot length, PVRN, TRN and RP index for LD222, April Bearded and their NILs ofRht genes

Shoot length (cm) PVRN1 TRN2 RP index3

LD222 origin

Rht-B1a Rht-B1a4 70.6 3.85 2.50 0.72 17.2 1.3 0.15 0.04

Rht-B1b Rht-B1b6 49.2 2.6 1.83 0.31 16.0 1.6 0.12 0.02

Significance7 ** ns ns ns

April Bearded origin

Rht-B1a Rht-B1a Rht-D1a Rht-D1a8 65.1 1.31,9 1.83 0.75 13.7 0.8 0.14 0.06

Rht-B1b Rht-B1b Rht-D1a Rht-D1a10 51.2 2.82 1.83 0.75 10.5 1.5 0.16 0.06

Rht-B1a Rht-B1a Rht-D1b Rht-D1b11 48.0 1.12 1.50 0.43 11.2 0.9 0.14 0.04

Significance12 ** ns ns ns

1The number of roots penetrating through the PV disc per plant.2The total number of seminal and crown roots per plant.3

The root penetration index (PVRN/TRN).4,8Recurrent parents of standard height.5Mean S.E. (n = 6).6,10Lines introgressed Rht-B1b gene.7,12,shows significant difference between or among NILs at P < 0.01 by t-test for LD222 origin and ANOVA for April Bearded origin;

ns: Not significant.9Thecommon letters withineach originat each traitare notsignificantly differentby themultipletestof Ryan-Einot-Gabriel-Welsch (P < 0.05).11Line introgressed Rht-D1b gene.

Table 2. Shoot length, PVRN,TRN andRP index forJennah Khetifa,

Cham1 and their RILs

Parents RILs

Jennah Khetifa Cham1 Mean CV (%)

Shoot length (cm) 74.4 4.01 45.1 0.72 59 .1 1 6

PVRN (plant1)3 6.67 1.45 3.00 1.00 3.5 0 4 7

TRN (plant1)4 17.7 0.9 16.0 3.5ns 17 .6 1 7

RP index5 0.38 0.09 0.18 0.02ns 0.2 0 4 3

ns: Not significant. 1Mean S.E. (n = 3).2and show significant difference between parents at 0.01 P

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The Reduced Height Genes Do Not Affect the Root Penetration Ability in Wheat