Resistance Sources to Brown Blotch Disease (Pseudomonas tolaasii) in a Diverse Collection of Pleurotus Mushroom Strains

Brown blotch disease (BBD) caused by Pseudomonas tolaasii is one of the most devastating diseases of Pleurotus spp. worldwide. Breeding for resistant strains is the most effective method for controlling BBD. To identify resistant germplasm for BBD management, 97 strains comprising 21 P. cf. floridanus, 20 P. ostreatus, and 56 P. pulmonarius were screened by two different methods; namely, inoculation of the pathogen on the mushroom pileus (IMP) and on the spawned substrate (IMSS) under controlled conditions. Out of the 97 strains screened, 22 P. pulmonarius, and four P. cf. floridanus were moderately resistant to BBD using the IMP method. Eleven P. pulmonarius, six P. cf. florida, and one P. ostreatus strains were highly resistant to BBD using the IMSS method. All of the 97 strains showed varying degrees of susceptibility using the IMP method, but eight strains were completely resistant using the IMSS method. Combining these two methods, five strains were highly resistant (four P. pulmonarius and one P. cf. floridanus) and 11 were moderately resistant (eight P. pulmonarius and three P. cf. floridanus). The resistance sources to P. tolaasii identified in P. pulmonarius and P. cf. floridanus could be used for further breeding of Pleurotus spp.