Identification, mycotoxigenic ability and biosynthesis genes of Alternaria spp. from apples in China

Alternaria toxins, as emerging mycotoxins, are common contaminants in apples and apple products. Nevertheless, the responsible Alternaria species, their ability to produce toxins, and the genes responsible for toxin biosynthesis remain ambiguous. In this study, 255 isolates of Alternaria were sampled from apple production areas in 14 provinces across China. Morphological and molecular biological identification indicated that toxin-producing isolates of Alternaria on apples consisted of 251 isolates of Alternaria alternata and 4 isolates belonging to the A. arborescens species complex (AASC). Using an UPLC-MS/MS detection method, the production of five types of Alternaria toxins-alternariol, alternariol monomethyl ether, altenuene, altertoxin I, and tentoxin-was assessed in all isolates. It was found that 254 isolates could produce more than one type of toxin, with altertoxin I having the highest detection rate and altenuene the lowest. PacBio-sequencing was conducted on the EOD115 isolate, and transcriptome sequencing was performed on toxin-producing variants EOD115 and EOD45-2, identifying the biosynthesis genes for these five Alternaria toxins using methods such as homologous alignment. These discoveries provide foundational genetic insights and theoretical data for future research on managing Alternaria toxins in apples.