Quantitative trait loci on chromosome 4B for coleoptile length and early vigour in wheat (Triticum aestivum L.)

The Norin-10 dwarfing genes, Rht-B1b (Rht1) and Rht-D1b (Rht2), are commonly used to reduce plant height and increase grain yield in wheat breeding programs. These dwarfing genes lower sensitivity of vegetative tissue to endogenous gibberellin to reduce cell and subsequent stem elongation. This reduction in cell elongation capacity reportedly results in a concomitant reduction in coleoptile length and early vigour (leaf area) thereby affecting seedling establishment and growth. A detailed genetic map from a cross between tall Halberd (Rht-B1a) and semidwarf Cranbrook (Rht-B1b) wheat cultivars was used to assess genetic factors affecting seedling growth. Parental and 150 doubled haploid progeny lines were characterised for seedling and height-related traits in controlled and field environments. Genotypic variation was large and predominantly under additive genetic control with evidence for transgressive segregation for some traits. Narrow-sense heritabilities were moderate to high (h2 = 0.31–0.91) indicating a strong genetic basis for differences between progeny. Molecular marker analyses identified a number of significant (P < 0.05) quantitative trait loci (QTL) for each trait. A major QTL, mapping directly to the Rht-B1 locus on chromosome arm 4BS, accounted for up to 49% of the genotypic variance in peduncle length and plant height, and 27–45% of the genotypic variance in coleoptile length across different temperatures. Another QTL, located close to the RFLP marker XksuC2 on the long arm of chromosome 4B, accounted for 15–27% of the genotypic variance in coleoptile length. The influence of the XksuC2-linked QTL on coleoptile length was greatest at 19˚C and decreased with cooler temperatures. The same QTL affected reductions in leaf size, and both coleoptile tiller size and presence to affect overall seedling vigour. There was also some evidence for epistatic interactions influencing coleoptile tiller growth. Reductions in plant size at the Rht-B1b and XksuC2 loci were associated with presence of the Cranbrook 4B allele. The negative genetic effect of the Rht-B1b dwarfing gene on early growth of wheat confirms phenotypic evidence of a pleiotropic effect of Rht-B1b on establishment and early vigour. Genetic increases in coleoptile length and early leaf area development are likely to be limited in wheat populations containing the Rht-B1b dwarfing gene.

[1]  G. Rebetzke,et al.  "Perfect" markers for the Rht-B1b and Rht-D1b dwarfing genes in wheat , 2002, Theoretical and Applied Genetics.

[2]  M. Gale,et al.  Differences in Leaf and Stem Anatomy Related to Plant Height of Tall and Dwarf Wheat (Triticum aestivum L.) , 1990 .

[3]  P. Langridge,et al.  Construction of three linkage maps in bread wheat, Triticum aestivum , 2001 .

[4]  Greg J. Rebetzke,et al.  Gibberellic acid-sensitive dwarfing genes reduce plant height to increase kernel number and grain yield of wheat. , 2000 .

[5]  C. Cockerham.  Covariances of Relatives from Self‐Fertilization1 , 1983 .

[6]  C. Haley,et al.  A simple regression method for mapping quantitative trait loci in line crosses using flanking markers , 1992, Heredity.

[7]  R. Littell.  SAS System for Mixed Models , 1996 .

[8]  D. Roff.  Evolutionary Quantitative Genetics , 1997, Springer US.

[9]  C. Bell,et al.  Establishment and yield of wheat (Triticum turgidum L.) after early sowing at various depths in a semi-arid Mediterranean environment , 1998 .

[10]  M. Perry,et al.  Yield improvement and associated characteristics of some Australian spring wheat cultivars introduced between 1860 and 1982 , 1989 .

[11]  B. Whan.  The emergence of semidwarf and standard wheats, and its association with coleoptile length , 1976 .

[12]  R. Doerge,et al.  Permutation tests for multiple loci affecting a quantitative character. , 1996, Genetics.

[13]  G. Rebetzke,et al.  Identification of quantitative trait loci for traits conferring weed competitiveness in wheat (Triticum aestivum L.) , 2001 .

[14]  R. Eastwood,et al.  Establishment and characterisation of wheat genetic mapping populations , 2001 .

[15]  R. Richards.  The Effect of Dwarfing Genes in Spring Wheat in Dry Environments. II.* Growth, Water Use and Water-use Efficiency , 1992 .

[16]  R. Allan.  Agronomic Comparisons Between Rht1 and Rht2 Semidwarf Genes in Winter Wheat , 1989 .

[17]  J. Wood,et al.  Drought resistance in spring wheat cultivars. III.* Yield associations with morpho-physiological traits , 1979 .

[18]  R. Richards.  The effect of dwarfing genes in spring wheat in dry environments, 1. Agronomic characteristics , 1992 .

[19]  J. Ransom,et al.  Improvement in the Yield Potential of Bread Wheat Adapted to Northwest Mexico 1 , 1986 .

[20]  E. Kirby.  Effect of sowing depth on seedling emergence, growth and development in barley and wheat , 1993 .

[21]  D. Paolillo,et al.  The Effects of Dwarfing Genes Rht1 and Rht2 on Cellular Dimensions and Rate of Leaf Elongation in Wheat , 1989 .

[22]  W. Schillinger,et al.  Winter Wheat Seedling Emergence from Deep Sowing Depths , 1998 .

[23]  R. Richards,et al.  The effect of rht genotype and temperature on coleoptile growth and dry matter partitioning in young wheat seedlings , 2001 .

[24]  Greg J. Rebetzke,et al.  Genetic improvement of early vigour in wheat , 1999 .

[25]  F. Salamini,et al.  Catalogue of gene symbols for wheat , 1998 .

[26]  Z. Zeng.  Precision mapping of quantitative trait loci. , 1994, Genetics.

[27]  M. Ganal,et al.  Genetic analysis of the dwarfing gene Rht8 in wheat. Part II. The distribution and adaptive significance of allelic variants at the Rht8 locus of wheat as revealed by microsatellite screening , 1998, Theoretical and Applied Genetics.