Genetic and chemotypic diversity of two lineages of Aspergillus flavus isolated from maize seeds of different agroclimatic niches of India

Maize is susceptible to colonization by Aspergillus flavus, which is the major aflatoxins producing fungus. Aflatoxins are fungal secondary metabolites that have been reported to adversely affect normal cell metabolism and seed germination. In this study, 106 maize seed samples were sampled across 13 states throughout India, and were screened for incidences of fungal infection. Among the seed samples collected across India nearly all maize seed samples were found to be infected with Aspergillus. All morphologically confirmed isolates belonging to Aspergillus section Flavi were subjected to various aflatoxin, biochemical, physiological and genotype assays, as well as phylogenetic analyses. Among 60 isolates tested, eight were non-aflatoxigenic in nature as determined by icELISA, and seven of those eight isolates showed absence of one or more aflatoxin cluster genes in PCR assay. The morphological, physiological and biochemical characterizations failed to show variation based on their toxigenicity. The phenetic and molecular genetic diversity could be observed based on RAPD and ISSR analyses and little isolate diversity could be determined based on geography or aflatoxigenicity. An inferred ITS sequence phylogeny segregated isolates into only two lineage groups: a large group I (including Ia and Ib) and small group II contained A. flavus isolates closely related to A. parasiticus. The current study highlights inherent diverse A. flavus infections, exhibiting a range of aflatoxin concentrations, that are present in maize seeds and they are important because of the potential threat to agricultural production and consumption.