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Abstract
Filamentous fungi in the Aspergillus section Nigri, the black aspergilli, are associated with several crops including maize, peanut, and grape where their infections can cause maize kernel rot, peanut blight, and grape rot, respectively. New evidence suggests black aspergilli can colonize plant tissue as endophytes. We developed a system to identify black aspergilli from peanut and maize in the southeastern United States. A survey indicated that 86.7 % (n= 150) of the isolates characterized by a rep-PCR system were A. niger, suggesting that this species complex is predominant in maize and peanut fields. To gain a better understanding of the plant-fungi interactions, we developed a genetic transformation system to generate fluorescent black Aspergillus strains. Microscopy showed that both A. niger and A. carbonarius fluorescent transformants colonized root tissue as intercellular hyphae, which is characteristic of endophytes. Plant experiments were carried out to determine the potential benefits of crop plants harboring endophytic fungi. Eleven black Aspergillus species were used to inoculate maize seeds, but only A. carbonarius and A. niger were able to systemically colonize seedlings; none of the isolates significantly promoted plant growth on two maize cultivars. In greenhouse studies in peanut, A. niger and its fluorescent transformants systemically colonized above and below-ground peanut tissue, but infections with both species had neutral effects on plant growth in the Florida 07 cultivar. We also tested the capacity of 150 isolates to produce fumonisins, carcinogenic secondary metabolites. We found that 27.8% (n=54) of the isolates produced FB1, 59.2% FB2, and 44.5% FB3. In conclusion, we report here that A. carbonarius and A. niger strains form endophytic associations with maize and peanut hosts. We also documented that some black Aspergillus isolates are capable of producing fumonisins.