Investigations on aflatoxin contamination in groundnut caused by aspergillus flavus (link ex. fries) and its management using pgpr (plant growth-promoting rhizobacteria)

Abstract

Aflatoxin contamination is a qualitative problem in groundnut (Arachis hypogaea L.) occurring at both pre-and post-harvest stages. These aflatoxins are secondary metabolites produced by Aspergillus flavus and A. parasiticus and have carcinogenic, hepatotoxic, teratogenic and immuno-suppressive effects. Use of plant growth-promoting rhizobacteria (PGPR) is a viable and sustainable option in managing aflatoxin problem in groundnut. The objectives of our present study were to evaluate the prevalence of A. flavus infection and aflatoxin contamination in groundnut oil mills/traders of Telangana and Andhra Pradesh (AP); differentiate toxigenic and atoxigenic strains using cultural methods; identify a superior PGPR (Pseudomonas fluorescens) isolate and determine its mode of inhibition on A. flavus and aflatoxin contamination. Pod samples were collected from eight selected oil mills/traders in Mahaboobnagar, Rangareddy, Nizamabad, Karimnagar (Telangana); and Anantapur (AP) districts and A. flavus infection was enumerated. Further, aflatoxin contamination in kernels was estimated by indirect competitive ELISA. A total of 24 A. flavus isolates were obtained from the collected pod samples. These isolates were identified as toxigenic/atoxigenic using cultural detection methods on Yeast extract sucrose (YES) media and coconut agar medium (CAM). Ten native P. fluorescens isolates from groundnut rhizosphere were isolated and screened against A. flavus by dual culture and in vitro seed colonization (IVSC) assays. Superior PGPR isolate (Pf7) against mold infection and aflatoxin contamination was screened for determining its mode of inhibition using scanning electron microscopy (SEM). In Telangana, kernel infection by A. flavus ranged from 42 (Mahaboobnagar) to 90.7% (Nizamabad). After Nizamabad, samples from Rangareddy district recorded up to 90% kernel infection. In AP, Tadimarri mandal recorded kernel infection up to 29.3%, whereas Tadipatri recorded up to 59.3%. Aflatoxins in kernels from these mills in Telangana were highest in Rangareddy (1205.2 μg kg-1) followed by Karimnagar (365.5 μg kg-1). Oil mills of Nizamabad and Mahaboobnagar have recorded aflatoxins to a tune of 4.9 and 11.5 μg kg-1in Telangana