Trait associations and allelic diversity at the Xgwm 261, Rht-B1, and Rht-D1 loci in winter wheat

Abstract

The semi-dwarfing genes Rht-B1b and Rht-D1b have been used extensively in the development of reduced height wheat (Triticum aestivum L.) cultivars. Yield increases have been observed through decreased lodging and improved partitioning of assimilates, although reduced stand from shorter coleoptiles and yield instability when grown in low yielding environments have been cited as disadvantages. Interest in the gibberellic acid sensitive semi-dwarfing gene Rht8 has increased since the discovery of Xgwm 261, a closely linked microsatellite marker, which may be useful as a diagnostic marker for Rht8. Two studies were conducted to assess allelic variation and trait associations of the Xgwm 261, Rht-B1 and Rht-D1, loci in winter wheat. The objectives of the first study were to determine allelic variation at the Xgwm 261 marker locus among historical and current Great Plains hard winter wheat germplasm, to characterize alleles at the Rht-B1 and Rht-D1 loci, and to evaluate the effects of these semi-dwarfing alleles on plant height, gibberellic acid (GA) sensitivity, and coleoptile length. Microsatellite markers Xgwm 261 (Rht8), BF-MR1 (Rht-B1), and DF-MR2 (Rht-D1) were used to determine the allelic identity at the Rht8, Rht-B1 and Rht-D1 loci. Plant height, GA sensitivity, and coleoptile length were evaluated in greenhouse and growth room conditions. Four allelic classes were characterized with the Xgwm 261 marker with fragment sizes of 165 bp, 174 bp, 192 bp, and 210 bp among 72 Great Plains entries: alleles at the Rht-B1 and Rht-D1 loci were also determined. This study was unable to verify the diagnostic capability of the Xgwm 261-192 bp microsatellite marker to identify germplasm with reduced height, gibberellic acid sensitivity, and a longer coleoptile suggesting the lack of linkage between Rht8 and Xgwm 261-192 bp in Great Plains germplasm. The objective of the second study was to determine the effects of allelic variation at the Xgwm 261, Rht-B1, and Rht-D1 loci on GA sensitivity, coleoptile length, and agronomic traits of two winter wheat recombinant inbred line (RIL) populations. The two populations ['Longhorn'/'Akron' (LA), Longhorn/'Yuma' (LY)] were planted at five locations in eastern Colorado for two years and measurements for plant height, grain yield, test weight, kernel weight, kernel number, heading date, and above ground biomass were recorded. Microsatellite markers Xgwm 261 (Rht8), BF-MR1 (Rht-B1), and DFMR2 (Rht-D1) were used to characterize the RIL populations. Gibberellic acid sensitivity and coleoptile length were evaluated in greenhouse and growth room conditions. Lower GA sensitivity and shorter coleoptile length was observed in RILs carrying the Rht-B1b allele compared with RILs carrying the Rht-B1a allele. Later heading date and taller plant height were consistently observed in RILs carrying the Xgwm 261-210 bp allele in combination with either Rht-B1b or Rht-B1a. Under the low yielding production conditions of the Great Plains region, the Xgwm 261-210 bp + Rht-B1a allelic class did not reduce grain yield and increased test weight.