RAPD and SCAR markers linked to resistance to frogeye leaf spot in soybean

Abstract

The soybean (Glycine max (L.) Merrill) frogeye leaf spot is caused by the fungus Cercospora sojina Hara and is a widespread disease in Brazil and other countries, causing severe losses in grain yield and also affecting seed quality. The availability of DNA markers linked to genes for resistance to this disease would accelerate breeding programs, particularly when other traits are also being evaluated. Bulked segregant analysis was applied to 3 F2 populations derived from crosses between the resistant cultivars Parana, Cristalina and Uberaba, and the susceptible cultivar Bossier. In the cross ‘Parana’ x ‘Bossier’, 2 RAPD markers were identified, CSOPA1800C and CSOPA21,250C, located at 4.4 ± 1.8 centiMorgans (cM) and 3.4 ± 1.7 cM respectively from the resistance locus. DNA fragments of similar molecular weight were observed in the population derived from the cross ‘Cristalina’ x ‘Bossier’ at 2.3 ± 1.2 and 4.7 ± 1.5 cM from the resistance locus, respectively. In the offspring of the cross ‘Uberaba’ x ‘Bossier’, a DNA fragment corresponding to marker CSOPA1800C was detected at 5.6 ± 2.1 cM from the resistance locus. Although marker CSOPA21,250C was not observed in this population, an additional marker was detected (CSOUB11,100C) at 6.7 ± 2.2 cM from the resistance locus. The 1,250 bp fragment of CSOPA21,250C was cloned and converted into a SCAR marker, which amplified a single fragment whose size corresponded to the cloned segment of the crosses involving cultivars Cristalina and Parana. Markers CSOPA1800C, CSOPA21,250C and CSOUB11,100C were mapped to soybean linkage group J with the aid of known SSRs linked to the Rcs3 locus, indicating that the RAPD and SCAR markers identified in our research also tag this resistance gene.