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

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 Xgwm261, 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 objective of the first study was to determine allelic variation at the Xgwm 261 marker locus among historical and current Great Plains hard winter wheat germplasm, characterize alleles at the Rht-B1 and Rht-D1 loci, and evaluate the effects of these semi-dwarfing genes on plant height, gibberellic acid sensitivity, and coleoptile length. Four allelic classes were characterized with the Xgwm 261 marker with fragment sizes of 165 bp, 174 bp, 192 bp, and 210 bp as well as alleles at the Rht-B1 and Rht-D1 loci among the 72 Great Plains entries. This study was unable to verify the diagnostic capability of the Xgwm 261-192 by microsatellite marker to identify germplasm with reduced height, gibberellic acid sensitivity, and longer coleoptile suggesting recombination of Rht8 with Xgwm 261-192 by in the Great Plains germplasm.; The objective of the second study was to determine the effects of 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 populations. Lower GA sensitivity and shorter coleoptile length was observed in RILs carrying the Rht-B1b alleles compared with RILs carrying the Rht-B1a alleles. Later heading date and taller plant height were consistently observed in RILs carrying the Xgwm 261-210 by 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 by + Rht-B1a did not reduce grain yield and increased test weight.