Archivio Journal of Plant Pathology

Abstract:

In September 2012, red spots located between the stipes and pilei of the fruiting bodies of Pleurotus nebrodensis whose growth had halted were observed in China. The internal transcribed spacer (ITS) and the D1/D2 domain of 26S rRNA gene from the putative pathogen, a bacterium isolated from diseases mushrooms, were amplified and sequenced (GenBank accession Nos. KF314800 and KF314802). The neighbour-joining tree constructed with ITS sequences showed that those of the bacterium under study had the highest similarity (99.2%) with the comparable sequences of Rhodotorula glutinis CBS 20T, while the D1/D2 domain sequences were identical with those of the same bacterial species. Metabolic profiles of the bacterial isolate from diseased mushrooms closely resembled that of R. glutinis CBS 20T with one exception (negative for acid production from fermentation of D-ribose). Based on the above, the putative pathogen was identified as R. glutinis. Pathogenicity tests carried out with suspensions (approximately 1×106 CFU/ml) directly inoculated on the surface of young P. nebrodensis fruiting bodies resulted in the development within 3-5 days of red spots like those shown by naturally diseases mushrooms. Negative controls did not develop symptoms. A bacterium identical to that used for inoculation trials was re-isolated from symptomatic mushrooms, thus fulfilling Koch’s postulates. Rhodotorula spp. are closely phylogenetically related to the genus Sporobolomyces, which was reported as the agent of the red spot disease of Pleurotus eryngii (Xu et al., 2014). To the best of our knowledge, this is the first report of R. glutinis-induced red spot disease of P. nebrodensis in China.