Analysis of protease activity in Aspergillus flavus and A. parasiticus on peanut seed infection and aflatoxin contamination

Abstract

Aspergillus flavus and A. parasiticus are aflatoxin-producing fungi that can infect peanut seeds in field crops. An association between A. parasiticus proteolytic enzyme activities and peanut fungal infection was examined. For this study, a model of inductive and non-inductive culture media to produce A. parasiticus extracellular protease before infection was used. These A. parasiticus cultures were used to infect peanut seeds of cultivars resistant and susceptible to aflatoxin contamination. Peanut seeds of both cultivars exposed to fungi grown on casein medium (inductive medium) showed higher internal and external infection and a higher fungal protease content than those observed on potato dextrose agar (PDA) and sucrose medium (non-inductive media). A further study showed higher fungal colonisation and aflatoxin contamination in seeds of the resistant cultivar preincubated with Aspergillus extracellular proteases than in those incubated without proteases. Moreover, protease activities affected the viability of noninfected resistant cultivar seeds, inhibiting germination and radicle elongation and enhancing seed tissue injury. The results strongly suggest that protease production by A. parasiticus is involved in peanut seed infection and aflatoxin contamination resulting in seed tissue damage, affecting seed viability and facilitating the access of fungi through the testa. The analysis of fungal extracellular proteases formed on peanut seed during infection showed that A. flavus and A. parasiticus produced metallo and serine proteases; however, there were differences in the molecular masses of the enzymes between both species. The greatest activity in both species was by serine protease, that could be classified as subtilase.

Genotypic Regulation of Aflatoxin Accumulation but Not Aspergillus Fungal Growth upon Post-Harvest Infection of Peanut (Arachis hypogaea L.) Seeds

“…It is known that aflatoxin contamination increases in seeds with low viability and germination rate [ 40 , 41 ]. In this study, instead of using seed sources from storage, all genotypes were grown in a common field and harvested at their respective optimum maturity dates.…”

Identification of genomic regions and diagnostic markers for resistance to aflatoxin contamination in peanut (Arachis hypogaea L.)

“…The external seed infection was measured by visual inspection using the percent seed infection index (PSII), which was investigated at 7 days after inoculation. Based on previous studies [ 21 ], the invasion level of A. flavus was defined and classified with minor modifications as Level 0 when no conidium observed on the seed surface; Level 1 when less than 1/3 of the seed surface covered by conidia; Level 2 when 1/3–2/3 of the seed surface covered by conidia; Level 3 when more than 2/3 of the seed surface covered by conidia. The formula was used to calculate the PSII, where n, n1, n2 and n3 are the number of seeds in total, level 1, level 2 and level 3, respectively.…”

Changes and induction of aminopeptidase activities in response to pathogen infection during germination of pigeonpea (Cajanas cajan) seeds

“…Fusarium oxysporum and Aspergillus niger are the fungi that infect many seeds at the time of germination and responsible for heavy losses (Asis et al, 2009). These fungi are found in the soil as saprophytes.…”