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Effect of semi-dwarf genes on the root penetration ability of wheat

Katashi Kubo1, Yutaka Jitsuyama1, Kazuto Iwama1, Nobuyoshi Watanabe2, Akira Yanagisawa3, Ismahane Elouafi4 and Miloudi M. Nachit4

1 Crop Science Laboratory, Department of Botany and Agronomy, Hokkaido University, Sapporo, 060-8589, Japan, www.agr.hokudai.ac.jp/botagr/sakumotsu/ Email k-kubo@res.agr.hokudai.ac.jp, y-jitsu@res.agr.hokudai.ac.jp, iwama@res.agr.hokudai.ac.jp
2
Department of Plant Genetics and Production, Faculty of Agriculture, Gifu University, Gifu, 501-1193, Japan, www.gifu-u.ac.jp/~watnb/Enghome.htm Email watnb@cc.gifu-u.ac.jp
3
Hokkaido Prefectural Kitami Agricultural Experimental Station, Tokoro, 099-1496, Japan, www.agri.pref.hokkaido.jp/kitami/ Email ayanagi@agri.pref.hokkaido.jp
4
International Center for Agricultural Research in the Dry Areas, P.O. Box 5466, Aleppo, Syria, www.icarda.cgiar.org/ Email I.Elouafi@cgiar.org, M.Nachit@cgiar.org

Abstract

The presence of semi-dwarf (Rht) genes in wheat may limit ability of roots to penetrate hardpans. This was tested by growing Rht and tall (rht) wheats in 15cm pots of vermiculite in which a thin paraffin:Vaseline (PV) disc had been inserted to simulate a hardpan at 10cm. Number of roots penetrating the PV disc (RNPV) and the total root number per plant (TRN) were measured at 8 wks after sowing. A root penetration (RP) index was calculated as RNPV/TRN. ‘Jennah Khetifa’ (rht type) had greater RNPV and RP index than ‘Cham 1’ (Rht type). But among 110 RILs derived from these parents, there was no association between shoot height and either RNPV, TRN or RP index. Other comparisons between near-isogenic wheats with and without Rht genes also showed no effect of Rht on RNPV, TRN or RP index. We conclude that RP ability of wheat is not affected by the presence of Rht genes.

Media summary

Root penetration ability of wheat into compacted soil is not affected by the semi-dwarf (Rht) genes, and has a quantitative nature of inheritance.

Key Words

drought avoidance, genetic control mechanism, root penetration, semi-dwarf (Rht) gene, soil compaction, wheat

Introduction

Water shortage is one of the most serious constraints to increased wheat yield in West Asia and North Africa (WANA) (Nachit 1998; Rajaram et al. 1996). Although water acquisition from deeper soil layer is beneficial for plants to avoid drought, the roots sometimes cannot extend to the deeper soil because of compacted soil layers, especially in drought years (Unger and Kaspar 1994). For stable crop production in the WANA region, increasing the root penetration (RP) ability under compacted soil conditions is an important breeding target. In our previous study, Ethiopian tall type (rht) landraces of durum wheat (Triticum turgidum L. var. durum) showed higher RP ability than semi-dwarf (Rht) varieties bred in North America (Kubo et al. 2004). From this result, we suspected that Rht genes might have some effect on the RP ability in wheat. In this study, we evaluated the relationship of the RP ability with Rht genes and the genetic control mechanism of RP ability in wheat.

Methods

Two durum wheat varieties, ‘Jennah Khetifa (JK; rht type)’ and ‘Cham1 (C1; Rht type)’, 110 RILs derived from a cross between JK and C1 (Nachit et al. 2001), a NIL of durum wheat for Rht-B1b gene and its recurrent parent ‘LD222’ (rht type), and two NILs of bread wheat (T. aestivum L.) for Rht-B1b and Rht-D1b genes and their recurrent parent ‘April Bearded’ (rht type) were examined in a polyhouse of Field Science Center for Northern Biosphere, Hokkaido University (Sapporo, Japan, 43゚N, 141゚E).

The pot for the evaluation of RP ability consisted of one 100 mm tall tube above one tube 50 mm tall (Figure 1). As a proxy of a compacted soil layer, a PV disc (a mixture of 40% paraffin and 60% Vaseline (Kubo et al. 2004), 3 mm in thickness, 60 mm in diameter, 0.36-0.57 MPa in hardness), was placed between the two tubes, which 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 to which was added 60, 100, 50 and 30 g/m3 of N, P2O5, K2O and MgO, respectively. The experimental design was a randomized complete block with three replications in JK, C1 and their RILs, and with six replications in ‘LD222’, ‘April Bearded’ and their NILs. The vermiculite below the PV disc in the pot was kept on water-saturated condition by absorbing the water from the bottom of the pot. The water content of the vermiculite above the PV disc in the pot was measured by the FDR soil moisture meter (DIK-311A, Daiki Rica Kogyo Co., Ltd., Tokyo, Japan), and adjusted to 50% by the irrigation when it decreased to 20%. At eight weeks after sowing (approximately the heading stage of wheat seedlings), the shoot length was recorded, and then the number of the roots penetrating through the PV disc per plant (RNPV) and the total root number per plant (TRN; the number of seminal roots + the number of crown roots) were counted after washing away the vermiculite from roots. RP index was calculated as the ratio of RNPV to TRN. Statistical analyses were done by the software SPSS (Ver.7.5.1J, SPSS Japan, Tokyo, Japan).

Figure 1. Diagram of the pot used in the experiment. Each pot was made from polyvinyl chloride tubes, having inside the PV disc (mixture of 40% paraffin and 60% Vaseline).

Results

Shoot length, which was affected by Rht gene, was higher in JK (rht genotype) than in C1 (Rht genotype) (Table 1). JK also had greater values in RNPV and RP index than C1, but not in TRN. In the RILs, RNPV and RP index showed higher coefficients of variation compared with the shoot length and TRN.

Table 1. Shoot and root traits for Jennah Khetifa, Cham1 and their RILs.

 

Parents

 

RILs

 

Jennah Khetifa

Cham1

 

Mean

CV (%)

Shoot length (cm)

74 11)

45 1

 

59

16

RNPV

6.7 1.5

3.0 1.0

 

3.5

47

TRN2)

18 1

16 4

 

18

17

RP index3)

0.38 0.09

0.18 0.02

 

0.20

43

1) Mean Standard error (n = 3). 2) The number of seminal + crown roots. 3) RNPV / TRN.

The shoot length of the RILs showed bimodal distribution. On the other hand, RNPV showed a continuous and normal distribution (Figure 2). Normal distributions were also shown in TRN and RP index (data not shown). RNPV had significant positive correlations with TRN (r = 0.398, P<0.01) and RP index (r = 0.922, P<0.01). There was no significant correlation between TRN and RP index (r = 0.050). The shoot length had no significant correlations with RNPV (r = 0.155), TRN (r = 0.096) and RP index (r = 0.050).

Figure 2. Frequency distribution for shoot length and RNPV in the RILs.

Significant difference was found in shoot length between recurrent parent (rht) and the NILs for Rht-B1b and Rht-D1b, but not in RNPV, TRN and RP index in both varieties (Table 2).

Table 2. Shoot length (cm), RNPV, TRN and RP index for LD222, April Bearded and NILs for Rht genes.

 

Shoot length
(cm)

RNPV

TRN

RP index

LD222 – rht

71 41)

2.5 0.7

17 1

0.15 0.04

LD222 – Rht-B1b2)

49 3

1.8 0.3

16 2

0.12 0.02

         

April Bearded – rht

65 1

1.8 0.7

14 1

0.14 0.06

April Bearded – Rht-B1b

51 3

1.8 0.7

11 2

0.16 0.06

April Bearded – Rht-D1b3)

48 1

1.5 0.4

11 1

0.14 0.04

1) Mean Standard error (n = 6). 2), 3) Lines introgressed with Rht-B1b and Rht-D1b, respectively.

Conclusion

RP ability of wheat was not affected by presence of Rht genes, and was controlled by polygenic mechanisms. From these results, it can be considered that developing high-yielding Rht varieties with excellent RP ability may be possible using this method to evaluate the RP ability.

References

Kubo K, Jitsuyama Y, Iwama K, Hasegawa T and Watanabe N (2004). Genotypic difference in root penetration ability by durum wheat (Triticum turgidum L. var. durum) evaluated by a pot with paraffin-Vaseline disc. Plant and Soil (in press).

Nachit MM (1998). Durum breeding research to improve dryland productivity in the Mediterranean region. In ‘SEWANA (South Europe, West Asia and North Africa) Durum Research Network’; Proceedings of the SEWANA Durum Network Workshop, 20-23 Mar 1995, Aleppo, Syria. (Ed. Nachit MM, Baum M, Porceddu E, Monneveux P and Picard E.) pp 1-15. ICARDA, Aleppo, Syria.

Nachit MM, Elouafi I, Pagnotta MA, El Saleh A, Iacono E, Labhilili M, Asbati A, Azrak M, Hazzam H, Benscher D, Khairallah M, Ribaut JM, Tanzarella OA, Porceddu E and Sorrelles ME (2001). Molecular linkage map for an interspecific recombinant inbred population of durum wheat (Triticum turgidum L. var. durum) Theoretical Applied Genetics 102, 177-186.

Rajaram S, Braun HJ and van Ginkel M (1996). CIMMYT’s approach to breed for drought tolerance. Euphytica 92, 147-153.

Unger PW and Kaspar TC (1994) Soil compaction and root growth: a review. Crop Science 86, 759-766.

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