ARS | Publication request: SOYBEAN BROWN STEM ROT RESISTANCE QTL IN 'BSR 101' AS EXPRESSED IN A GROWTHCHAMBER ENVIRONMENT

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 1998
Publication Date: N/A

Interpretive Summary: Brown stem rot is one of the most frequently occurring and devastating diseases of soybean. It causes grain yield loss reported as high as 66%. Although three genes for resistance have been identified, traditional breeding methods have been slow to develop resistant cultivars with high grain yield and other good agronomic traits. The primary obstacle to development of high yielding resistant lines is the high variability of disease expression. Therefore, development of high-yielding resistant cultivars would be greatly facilitated by the availability of molecular markers known to be very closely associated with the resistance gene(s). These authors identified such molecular markers in the resistant public cultivar BSR 101. They found that two sets of molecular markers were associated with resistance; one accounting for the majority of non- environmental variability observed, and a second accounting for a lesser association. Molecular markers associated with resistance are identified and are available for use by breeders interested in developing resistant high yield lines and for use by geneticists interested in cloning the resistance genes. The markers associated with the lesser association were developed previously with the intention of identifying candidate resistance genes, and these results indicate that they may do exactly that. The two genetic regions associated with resistance are very near each other on the soybean chromosome. Such physically close regions often have been missed by other studies. This study illustrates to other scientists the utility and power of the new mapping approaches and reports a previously undiscovered resistance gene.

Technical Abstract: Brown stem rot, caused by the soil born fungus Phialophora gregata, is one of the most frequently occurring and devastating diseases of soybean [Glycine max (L.) Merr], with grain yield loss reported as high as 66%. Although three dominant genes for resistance, Rbsl, Rbs2, and Rbs3, have been identified, traditional breeding methods have been slow to develop resistant cultivars with high grain yield and other good agronomic traits. The primary obstacle to development of high yielding resistant lines is low heritability of resistance. The primary objective of this study was to map the gene(s) conferring resistance to brown stem rot in the resistant public cultivar BSR 101, thereby identifying several molecular markers for use in marker assisted selection. A population of 320 recombinant inbred lines (RIL) in the F6:7 generation was derived from a cross of BSR 101 and PI 437.654. Foliar and stem infection data were recorded from three inoculated seedlings of each RIL and parent grown in each of two growth chambers. MAPMAKER, SAS regression analysis, interval mapping with MAPMAKER QTL, and composite interval mapping with QTL CARTOGRAPHER Model 6 were used to map and associate molecular markers with resistance. All analyses identified markers on Linkage Group J, and QTL CARTOGRAPHER with Model 6 provided dramatically greater precision. QTL CARTOGRAPHER identified two linked QTL: a major QTL between AFLP markers AAGATG152E and ACAAGT260, and a minor QTL between markers RGA31-3 and RGA3I-2. The smaller QTL associated with the cluster of RGA3 loci is of special interest, because it is the first example of a disease resistance QTL associated with a resistance gene analog.