Screening and genetics of resistance to purple seed stain caused by Cercospora kikuchii in soybean

A total of 123 diverse soybean germplasm representing maturity groups (MG) III, IV, and V were screened in the field with natural infection and artificial inoculation for resistance to purple seed stain (PSS) caused by Cercospora kikuchii. Data on percentage of Cercospora leaf blight, percentage of visual PSS and percentage of C. kikuchii infection indicated differential responses for MGs, plant introduction (PI) accessions, and between inoculation treatments. Maturity group III and IV accessions were more susceptible than MG V accessions. There was a strong positive correlation between visual PSS and C. kikuchii infection, and between natural infection and artificial inoculation. A total of 16 PIs from MG III and IV were identified as resistant genotypes for PSS. Inheritance of PSS resistance in PI80837 was evaluated using F2:5 lines derived from AP350 x PI80837 and PI80837 x MO/PSD-0259. Percentages of PSS and of C. kikuchii infection were evaluated for the parents and the F 2:5 lines. Range of the parents and confidence interval were used to classify resistant and susceptible reactions in the F2:5 lines. Sixteen SSR markers from LG-G between Sat_131 and Satt303 were used to screen the parents and the F2.5 lines. From phenotypic and genotypic data we confirmed the presence of a candidate resistance gene Rpss1 linked to Satt115 and Satt340 on LG-G in PI80837 and also identified an additional putative gene for PSS resistance.