Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/11/2003
Publication Date: 7/1/2003
Citation: Bai, G., Das, M.K., Carver, B.F., Xu, X., Krenzer, E.G. 2003. Covariation for microsatellite marker alleles associated with rht8 and coleoptile length in winter wheat. Crop Science. 44:1187-1194. Interpretive Summary: Cleoptiles are the first leaves that appear above ground. Wheat (Triticum aestivum L.) cultivars with longer coleoptiles are preferred in dryland regions and in early-planted management systems of the Great Plains. Gibberellic acid (GA3), a plant growth hormone, may play a role in promoting coleoptile elongation. However, many modern cultivars are insensitive to GA3 due to the presence of dwarfing genes and therefore tend to have short coleoptiles. Fortunately, the gene Rht8 can reduce plant height and also sensitivity to GA3. Recently a molecular marker diagnostic for Rht8 has been discovered. Rht8 can be an alternative in modern wheat cultivars to replace GA3 insensitive dwarfing genes. Our objectives were to survey the presence of Rht8 gene in collections of hard winter and soft red winter wheat. Results were compared to samples of Chinese accessions from a Rht8-rich geographic region, and coleoptile lengths of cultivars with and without were compared. About 8% of all U.S. accessions carried the molecular marker diagnostic for Rht8, compared with 64% of the Chinese accessions. Coleoptile length varied among accessions from 4.4 cm to 11.4 cm. Coleoptiles for cultivars containing the Rht8 diagnostic marker were not significantly longer than those without the marker. Since coleoptile elongation may be controlled by several genes, using Rht8 gene alone may not be sufficient to select coleoptile length in a semidwarf plant type.
Technical Abstract: Wheat (Triticum aestivum L.) cultivars with greater coleoptile elongation are preferred in low-precipitation dryland regions and in early-planted management systems of the Great Plains, but the presence of GA3-insensitive dwarfing genes tends to restrict coleoptile elongation. The agronomic value of Rht8 and the discovery of its diagnostic microsatellite marker, Xgwm 261, have accelerated breeders' interest in Rht8 as an alternative dwarfing gene. Our objectives were to determine allelic distributions at the marker locus in contemporary samples of hard winter and soft red winter wheat relative to samples of Chinese accessions from a Rht8-rich geographic region, and to compare coleoptile elongation in the presence or absence of Rht8 determined by the Xgwm 261 marker. The 165-bp (primarily hard winter wheats) and the 174-bp (primarily soft red winter wheats) alleles of Xgwm 261 were most frequent. About 8 % of all U.S. accessions carried the 192-bp allele diagnostic for Rht8, compared with 64% of the Chinese accessions. Coleoptile length varied among accessions from 4.4 cm to 11.4 cm. Frequency distributions for 192-bp and non-192-bp genotypes showed no advantage of the 192-bp allele to coleoptile elongation. None of the 192-bp genotypes from the Great Plains showed greater coleoptile length than 'TAM 107', a hard red winter cultivar without Rht8 often chosen over contemporary cultivars for its greater emergence capacity with deeper seed placement. Since coleoptile elongation may be controlled by several quantitative trait loci, identifying only the presence of 192-bp allele of Xgwm 261 may be misleading if the primary motivation for its deployment is to increase coleoptile length in a semidwarf plant type.