Comparative genomic studies of Penicillium spp. that cause blue mold of apple fruit in storage reveal genetic features likely involved in virulence and mycotoxin production

Blue mold decay of apples and pears during storage is caused by Penicillium species in the United States and in many countries worldwide. This fungal mold is responsible for severe economic losses and produces an array of mycotoxins that contaminate processed apple products.  P. expansum is the most prevalent among the species, causing more than 50 percent of the postharvest decay during storage. P. solitum is less virulent compared with P. expansum but also causes blue mold decay. To analyze the genetic mechanisms contributing to pathogen virulence, spore germination, and mycotoxin production, the whole genomes of P. expansum (R19 isolate) and P. solitum (RS1 isolate) were sequenced. The raw sequences of P. expansum and P. solitum were assembled into 16 and 7 scaffolds with N50 equals 8.2 Mbp and 7.7 Mbp respectively. The genomes are estimated to contain 32.9 Mbp and 35.8 Mbp respectively. Annotation indicated that there are about 10,560 and 10,672 coding genes in each genome. Using a comparative approach, we profiled unique gene sets in each species, which are 224 and 285 unique genes in P. expansum and in P. solitum respectively. The genes that are putatively involved in virulence and mycotoxin production are identified. Better understanding of the infectious mechanism of these target genes could contribute to devising specific strategies to control blue mold decay on apples and pears during storage.