Biological and Molecular Characterization of Four Botryosphaeria Species Isolated from Pear Plants Showing Stem Wart and Stem Canker in China

Pear stem wart and pear stem canker, which have been considered as two different fungal diseases caused by pathogens belonging to Botryosphaeria spp., commonly occur and cause serious damage in the main pear-producing areas in China. To identify the species of this genus infecting pear in China, 131 Botryosphaeria isolates were recovered from pear samples exhibiting symptoms collected from 20 different provinces and areas. Morphological characterization and phylogenetic analyses of the ribosomal DNA internal transcribed spacer region and the beta-tubulin and EF1-alpha genes revealed that Botryosphaeria dothidea, B. rhodina, B. obtusa, and B. parva were associated with different pear stem wart and stem canker symptoms. Remarkably, all isolates of B. dothidea were obtained from the samples showing either stem wart or stem canker lesions; however, the isolates of the other three species were obtained only from the samples showing stem canker. Pathogenicity tests on the pear shoots showed that B. dothidea isolates could induce stem wart or stem canker lesions but all the isolates of the other three species could only induce stem cankers. However, the isolates of B. parva, B. rhodina, and B. obtusa exhibited higher virulence than that of the B. dothidea isolates on the pear fruit. Our results suggest that B. dothidea is the common causal agent for these two diseases (a pear stem wart and a pear-related stem canker), whereas B. parva, B. rhodina, and B. obtusa only cause pear stem canker diseases. To our knowledge, this study represents the first report for biological and molecular characterization of four Botryosphaeria spp. isolated from pear plants showing stem wart and stem canker in China.