The efficacy of marker-assisted selection for grain mold resistance in sorghum

Five breeding populations were created by crossing elite U.S. sorghum parental lines (RTx430, RTx436, BTx631, BTx635, and Tx2903) with ‘Sureño’, a dual purpose grain mold resistant sorghum cultivar. Molecular markers associated with five previously-reported quantitative trait loci (QTL) for grain mold resistance originating in ‘Sureño’ were used to determine if their presence enhanced selection for grain mold resistance in these populations. The allelic status of 87 F4 lines, with respect to these QTL, was determined using both simple sequence repeats (SSR) and amplified fragment length polymorphism (AFLP) markers. All 87 F4:5 lines and their parental lines, were evaluated for grain mold resistance in replicated trials in eight diverse environments in South and Central Texas during the summer of 2002. The effects of each allele from the grain mold resistant parent ‘Sureño’ were determined across and within all five populations, within individual environments, and in each population x environment combination. With a few exceptions, the QTL were effective in reducing grain mold susceptibility only within the RTx430/Sureño progeny, the identical cross that was used in the original mapping study. The results indicate that while that these alleles do confer additional grain mold resistance, they are only selectable in the original mapping population. This fact limits their potential usefulness in an applied breeding program.