Contribution of root-knot nematodes to aflatoxin contamination in peanut (Arachis hypogaea)

Authors: Timper, Patricia - Patty; WILSON, D - University Of Georgia; Holbrook, Carl - Corley

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2013
Publication Date: 7/1/2013
Publication URL: http://dx.doi.org/10.3146/PS12-14.1
Citation: Timper, P., Wilson, D.M., Holbrook Jr, C.C. 2013. Contribution of root-knot nematodes to aflatoxin contamination in peanut (Arachis hypogaea). Peanut Science. 40:31-39.

Interpretive Summary: Peanut kernels are susceptible to colonization by Aspergillus fungi which, under conditions of drought and high temperatures, can produce potent carcinogens known as aflatoxins. Our primary objective was to determine the mechanism by which the peanut root-knot nematode increases aflatoxin contamination in peanut before harvest. We determined 1) the role of nematode infection of roots vs. pods in increased aflatoxin contamination and 2) whether increased aflatoxin production in nematode-infected peanut is due to a greater percentage of small or immature kernels. A secondary objective was to determine whether a peanut cultivar with resistance to would reduce the risk of preharvest aflatoxin contamination in soil infested with the nematode. In the greenhouse, we physically separated root growth from pod set and inoculated each location with root-knot nematodes or a water control. The experiment was conducted six times. In one trial of the experiment, aflatoxin concentrations were increased by adding the nematodes to the pod zone. However, we found that root infection by the nematode was more consistently associated with elevated aflatoxin concentrations than pod infection. Another experiment was conducted with two peanut varieties (Tifguard and TifGP-2) and two nematode treatments (with and without root-knot nematodes). The variety Tifguard is resistant to root-knot nematodes and TifGP-2 is susceptible. The experiment was carried out in 24 field microplots equipped with a rainout shelter and was conducted five times from 2006 to 2010. Infection of TifGP-2 by the nematode did not lead to greater percentages of small kernels. In only one year (2007), nematodes appeared to increase the percentage of damaged kernels, though aflatoxin concentrations were not affected by nematodes in that year. In the rainout shelter experiment, 2006 was the only year where nematode infection of peanut increased aflatoxin concentrations. In that year, there were lower aflatoxin levels in the resistant variety Tifguard than the susceptible variety TifGP-2.

Technical Abstract: Peanut kernels are susceptible to colonization by Aspergillus spp. which, under conditions of drought and high temperatures, can produce aflatoxins prior to harvest. Our primary objective was to determine the mechanism by which the peanut root-knot nematode (Meloidogyne arenaria) increases aflatoxin contamination in peanut. We determined 1) the role of nematode infection of roots vs. pods in increased aflatoxin contamination and 2) whether increased aflatoxin production in nematode-infected peanut is due to a greater percentage of small or immature kernels. A secondary objective was to determine whether a peanut cultivar with resistance to M. arenaria would reduce the risk of preharvest aflatoxin contamination in soil infested with the nematode. In the greenhouse, we physically separated root growth from pod set and inoculated each location with M. arenaria or a water control in a 2x2 factorial design with 12-15 replications. The experiment was conducted six times. In one trial of the experiment, aflatoxin concentrations were increased by adding M. arenaria to the pod zone. However, we found that root infection by the nematode was more consistently associated with elevated aflatoxin concentrations than pod infection. Another 2 x 2 factorial experiment was conducted with two peanut genotypes (Tifguard and TifGP-2) and two nematode treatments (with and without M. arenaria) with six replications. The cultivar Tifguard is resistant to M. arenaria and TifGP-2 is susceptible. The experiment was carried out in 24 field microplots equipped with a rainout shelter. The experiment was conducted five times from 2006 to 2010. Infection of TifGP-2 by M. arenaria did not lead to greater percentages of small kernels. In only one year (2007), nematodes appeared to increase the percentage of damaged kernels, though aflatoxin concentrations were not affected by nematodes in that year. In the rainout shelter experiment, 2006 was the only year where nematode infection of peanut increased aflatoxin concentrations. In that year, there were lower aflatoxin levels in the resistant cultivar Tifguard than the susceptible germplasm TifGP-2 (12 vs. 136 ng/g).