Coleoptile Length Evaluation in Winter Wheat

In the northern Great Plains, optimum fall establishment is critical for winter survival of winter wheat (Triticum aestivum L.). The length of the coleoptile (protective sheath that covers the shoot during emergence) has been associated with fall stand establishment, most notably with semidwarf wheat cultivars that possess the Rhtl and/or Rht2 dwarfing genes. While coleoptile length evaluation and improvement is an objective of many breeding programs, little information is presently available to guide effective evaluation and improvement efforts. The objectives of this study were to assess the presence and nature of genotype x environment ( G x E) interaction for coleoptile length in South Dakota, to determine the inherent precision of a common coleoptile length screening procedure, and to characterize the coleoptile length of a collection of semidwarf and standard height Great Plains winter wheat germplasm. Seeds from forty five winter wheat genotypes (experimental lines and released cultivars) harvested at Selby, Winner, Wall, and Dakota Lakes-Irrigated in 1995 were used in a study of G x E interaction and seeds from fifteen winter wheat genotypes harvested at Selby (high test weight) and Winner (low test weight) in 1995 were used in a repeatability study. Seeds of 143 winter wheat genotypes from the Uniform Winterhardiness Nursery (UWHN)-southern Great Plains section and 13 1 winter wheat genotypes from the UWHN-northern Great Plains section were used to characterize the coleoptile length of semidwarf and standard height Great Plains winter wheat germplasm. Forty seeds of each genotype were germinated for coleoptile length evaluation. The analysis of variance showed that there were highly significant (P\u3c0.01) differences among genotypes at each environment. Genotype x environment interactions at the four locations were highly significant. Spearman\u27 s rank correlations between genotype means at the four environments were highly significant (rs= 0.93-0.95; P\u3c0.01), suggesting that G x E interactions were caused by differences in scale among the environments and not by differences in genotype rankings. Estimates of repeatability ( the theoretical upper limit of heritability) of coleoptile length measurements was high (Selby: 0.66 ± 0.10; Winner: 0.63 ± 0.11). Calculations of the gain in accuracy from multiple measurements suggested that two measurements are optimum for determining coleoptile length. Based on the Z values for coleoptile length, eighteen genotypes with Rht1 and/or Rht2 (determined with gibberellic acid testing) from the southern Great Plains region and eight from the northern Great Plains region were found to have long coleoptiles. Four gibberellic acid-sensitive semidwarf genotypes with long coleoptiles were identified from the northern Great Plains section, suggesting the presence of the Rhts or Rht9 semi dwarfing genes. The results from this study indicate that genetic progress for coleoptile length is possible and that seed quality has little, if any, influence on the conduct of the test or results derived therefrom. Semidwarf genotypes with long coleoptiles seem to exist among the southern and northern Great Plains winter wheat breeding programs. These genotypes may be useful to wheat breeders interested in incorporating Rht gene(s) into their breeding materials while maintaining coleoptile length