Abstract:

Aspergillus flavus is commonly regarded as a kind of saprophytic fungi with a wide distribution. It is the major aflatoxin B (AFB) and cyclopiazonic acid (CPA) producing species, as well as a pathogen to humans and animals. In the world, huge amounts of corns, peanuts and cotton seeds are vulnerable to be contaminated by A. flavus and aflatoxin each year. There is much variance in morphological, genetic and toxin-producing characters among isolates of A. flavus, resulting in its ambiguous population structure. In this paper, we analyzed 88 isolates of A. flavus from different environments of 26 provinces (including the Greater and Lesser Khinggan Mountains) in China, as well as nine ex-types and authentic strains based on CaM and benA sequences to infer their sequence types (STs) using multi-locus sequence typing (MLST), and their phylogenetic relationships and population structures employing MEGA 6.0 and Structure 2.3.4 softwares, together with their toxin-producing features (AFB and CPA). Our results showed that the 88 Chinese isolates and nine ex-type and authentic strains were distributed in three populations, i.e. A. flavus population I, A. flavus population II and population A. oryzae. There were 17 STs among the 97 isolates, among which the 88 strains from China were distributed in 15 STs. All isolates of population A. oryzae did not produce AFB, but most isolates of the A. flavus populations I and II produced AFB and CPA. The toxin-producing features were strain-specific, but not correlated to sequence types or populations. Some correlations between toxin-producing characters and geographical environments or crop types were recognized. The isolates of A. flavus populations I and II from the northeast areas planting corns, the arid northwest planting cottons and the south areas growing peanuts all produced AFB and CPA. The isolates from Hoh Xil of Qinghai and Aba of Sichuan did not produce AFB, though with the production of CPA. The isolates of A. oryzae population without AFB production were almost from North China with diverse climates and geographical environments, where the traditional Chinese soybean paste is made in the rural areas.

Key words: diversity, genetic markers, mycotoxins, orthologous genes, phylogenetics