Location: Sunflower Research
2012 Annual Report
White mold a devastating disease of dry beans is caused by the fungus Sclerotinia sclerotiorum. This funguscauses severe and capricious yield loss in dry bean (Phaseolus vulgaris L.) especially in North Dakota and Minnesota, which are ranked as top producers of dry beans in 2010. Identification and development of resistant genotypes like G112, ICA-Bunsi, PC–50, I9365-25, A195, and A55, among others, has helped to gain some resistance to white mold, but most of these lines are difficult to use in breeding programs because of issues with linkage drag.During the 2009 growing season, good levels of field resistance to white mold were found in breeding lines ND060514 (navy) and ND080547 (small red) from the NDSU dry bean breeding program. The high levels of resistance were later confirmed by additional screenings in the field and the greenhouse. These two lines, some of its parents, susceptible checks, and some known sources of resistance, were screened with molecular markers previously reported to be linked to resistance loci. Seeds from both resistant lines ND060514 and ND080547 were planted in the greenhouse along with some resistant parents and susceptible parents. DNA was extracted from all genotypes using the emerging trifoliate leaves by the CTAB method. A total of 204 IN-DEL Scaffold markers, 17 RAPD (Random Amplification polymorphism DNA) markers, 2 SRAP (Sequence-related amplified polymorphism) markers, 6 SCAR (Sequenced Characterized Amplified Region) markers, and 7 SSR (Simple Sequence Repeats) markers linked loci for resistance to white mold were found in BIC (Bean Improvement Cooperative) website and in Soule et al. (2011). Images were obtained for each marker in order to observe polymorphism and possible associations among genotypes and markers. A total of 237 markers were screened, only 94 Scaffold markers, 5 RAPD markers, 1 SRAP markers, 2 SCAR markers, and 2 SSR markers showed polymorphism. There were 34 markers that were monomorphic and 35 primers did not amplify any of the genotypes. The resistant lines ND060514 and ND080547 were compared with other resistant and susceptible genotypes and with parents. These lines showed similarities when compared with each other in scoring with almost all of the polymorphic markers. The pedigree of resistant line ND060514, which involves parents like ICA-Bunsi (resistant genotype), Raven, and 115M (susceptible genotype) showed lots of dissimilarity in the bands with many polymorphic markers. When resistant lines were compared with breeding line ND060514, it showed 76 times similar bands with ICA-Bunsi, 75 times with A55, 74 times with G112, 70 times with I9365-31, 73 times with Aztec, 30 times with CO72542, 65 times with VA19, 81 times with Newport, 85 times with Huron. Similar results were observed in case of resistant line ND080547, whose parental lines are Buster and Vax3 which are susceptible to the disease. Breeding line ND080547 showed 69 times shared same markers with Bunsi, 76 times with A55, 32 times with G112, 83 times with I9365-31, 88 times with Azetec, 80 times with CO72542, 72 times with VA19, 75 times with Newport and 76 times with Huron. Given the fact that ICA-Bunsi is one of the parents of this line, it is not surprising to find these similarities. The case of breeding line ND080547 is more difficult because both parents have been reported as susceptible in previous studies. Differences were found not only in the scoring of ND060514 and ND080547 which are resistant lines when compared with their parents but also with all other resistant genotypes susceptible and genotypes. We are currently in the process of identifying the loci associated with each one of these markers in order to have a better understanding of the genes involved in the resistance of these lines. In addition, we are repeating the markers that did not amplify in order to check for problems in the protocols used. We hope to have a solid baseline in the near future that will allow us to further expand the study of the resistance contained in ND080547.