Submitted to: Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation
Publication Type: Abstract Only
Publication Acceptance Date: October 21, 2007
Publication Date: March 5, 2008
Repository URL: http://www.ars.usda.gov/Services/docs.htm?docid=12564
Citation: Timper, P., Holbrook, Jr., C.C. 2007. Getting to the root of nematode involvement in aflatoxin contamination of peanut [abstract]. Proceedings of the 2007 Annual Multicrop Aflatoxin/Fumonisin and Fungal Genomics Workshop, October 22-24, 2007, Atlanta, GA. p. 115. Technical Abstract: Infection of peanut by root-knot nematodes (Meloidogyne arenaria) can lead to an increase in aflatoxin contamination of kernels when the plants are subjected to drought stress during pod maturation. The nematode can infect both the roots and peanut pods. We recently showed that root infection in the absence of pod infection by M. arenaria can lead to greater aflatoxin contamination in the kernels; however, it is not known whether wounding of pods by nematodes can also play a role in aflatoxin contamination by serving as entry points for toxigenic Aspergillus spp. Our objectives were: 1) to determine the contribution of pod galling caused by root-knot nematodes to the increase in aflatoxin contamination, and 2) to determine whether nematode-resistant peanut genotypes reduce the risk of preharvest aflatoxin contamination in soil infested with root-knot nematodes. A greenhouse experiment was conducted in which pods and roots were physically separated. Pod set was restricted to soil-filled pans (41 cm dia. x 10 cm depth), while the roots grew underneath the pan into a pot. The experiment had a factorial arrangement of treatments: pod zone with and without nematodes, and root zone with and without nematodes. The four treatment combinations were replicated 10 to 13 times. Grain infested with Aspergillus flavus/A. parasiticus was added to the soil surface (pods zone) at mid bloom. Plants were subjected to drought stress 40 days before harvest. In both 2004 and 2005, there was very little pod galling from M. arenaria, and there was no difference in aflatoxin concentrations between treatments with and without nematodes in the pod zone. In 2006, there was heavy pod galling with galls present on 53% of the pods. We also found greater aflatoxin concentrations in the kernels when nematodes were added to the pod zone than when they were not (572 vs 19 ppb; P = 0.03). In the 2006 experiment, nematode infection of roots had no effect of aflatoxin concentrations in the peanut kernel. Based on these and previous results, it appears that nematode infection of either the roots or pods can lead to greater aflatoxin contamination of peanut kernels. A field microplot study was conducted in 2006 to determine whether there was lower aflatoxin concentrations in nematode-resistant than in susceptible peanut when exposed to M. arenaria. Two sister lines with good resistance to Tomato Spotted Wilt Virus were used: C724-19-15 which is highly resistant to M. arenaria and C724-19-25 which is susceptible to the nematode. Half of the 24 plots were inoculated with nematodes at two different times (at plant and after pegging) and the other half were not inoculated with nematodes. There were six replicates of each treatment combination. All plots were inoculated with A. flavus/A. parasiticus. Drought was induced 5 to 6 weeks before digging. Root-galling from M. arenaria was so severe in the susceptible peanut that kernel yield averaged only 14 g compared to kernel yields of 218 to 234 g in the resistant peanut and the susceptible peanut without nematodes. Aflatoxin concentrations were also greater (P = 0.04) in the susceptible peanut (137 ppb) than in the resistant peanut (12 ppb). This experiment will need to be repeated to confirm that aflatoxin contamination of peanut in soil infested with M. arenaria is reduced when a nematode-resistant peanut is grown.