Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 15, 2006
Publication Date: December 15, 2006
Repository URL: http://www.ars.usda.gov/Services/docs.htm?docid=12564
Citation: Timper, P., Holbrook, Jr., C.C. 2006. Root-knot nematodes and aflatoxin contamination in peanut [abstract]. Proceedings of the 2006 Annual Multicrop Aflatoxin/Fumonisin and Fungal Genomics Workshop, October 16-18, 2006, Fort Worth, TX. p. 90. 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 2006, there was heavy pod galling, but we have not yet determined aflatoxin concentrations in the kernels. A field microplot study was conducted in 2004 and 2005 to determine whether there was lower aflatoxin concentrations in nematode-resistant than in susceptible peanut when exposed to M. arenaria. In 2004, a moderately resistant peanut (C209-6-60) was used and in 2005, a highly resistant peanut (C725-25) was used. In both years GA 02C was the susceptible peanut. 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. In 2004, root-galling from M. arenaria was so severe that only 3 of 240 susceptible peanut plants survived to crop maturity and no peanuts were present on the dead vines. The gall index (0 – 10 scale) on the moderately resistant peanut was 6.7. However, despite this moderately high galling, there was no difference in aflatoxin concentrations between plots with and without nematode inoculum. In 2005, root galling was mild with indices of 1.9 on the susceptible peanut GA 02C. Nematode inoculation had no effect on aflatoxin concentrations; however, GA 02C had lower (P = 0.005) concentrations of aflatoxin in sound, mature kernels than did C725-25 (77 vs 886 ppb). Further studies are needed to confirm whether GA 02C has resistance to preharvest aflatoxin contamination.