Nematode Community Structure and Effects on Peanut Production Systems

Abstract

Understanding the total nematode community in agronomic systems and its impact on crop health may provide insight into more sustainable management strategies. In this study the focus was on management of the peanut root-knot nematode, Meloidogyne arenaria race 1 and the aflatoxigenic fungi Aspergillus flavus and A. parasiticus, a toxic food contaminate that poses a threat to humans and animals, to increase peanut yields while lowering toxins. The overall approach of management is to suppress plant-parasitic nematodes that facilitate invasion of the toxin producing fungi through manipulation of free-living nematode populations that act to increase plant health. The objectives of this research were 1) evaluate nematode consensus primers and Denaturing Gradient Gel Electrophoresis (DGGE) techniques for effectiveness in identification of nematode populations and monitoring community shifts; 2) develop nematode genetic profiles of selected soil samples, using DGGE fingerprinting, from different rotation sequences: continuous peanut, continuous bahiagrass, peanut/cotton, and peanut/corn, to determine if any factors exist that result in nematode population shifts; and 3) identify individual populations in the nematode community and determine their relationship with peanut yields and aflatoxin contamination. Nematode populations were established through various methods including in vitro culturing methods, after which total genomic DNA was extracted from each species to evaluate the specificity of nematode consensus primers. The primers amplified a wide trophic range of nematode DNA and fungal DNA, showing that the primers may be universal to all eukaryotes. DGGE techniques were then evaluated by amplifying a portion of the 18S rDNA per species collected and subsequently separating the species through denaturing gradient gel electrophoresis. The DGGE technique successfully separated nematodes at the generic level. Nematode genetic profiles were created from peanut soils under different cropping sequences which revealed individual banding patterns, indicating population shifts between rotation sequences and shifts between sampling periods. Free-living nematodes accounted for the majority of sequences recovered from profiles, although plant-parasitic, animal-parasitic, and entomopathogenic nematodes, as well as nematophagus fungi were identified in recovered sequences. Bahiagrass rotations supported higher population levels of microbivore nematodes and significantly lower levels of aflatoxins when planted in rotation with peanuts. Negative correlations occurred between microbivore populations and total aflatoxin levels, suggesting that free-living nematodes may play a role in the suppression of aflatoxin contamination in peanuts.