Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 9/15/2003
Publication Date: 12/15/2003
Citation: Timper, P., Wilson, D.M., Holbrook Jr, C.C. 2003. Root-knot nematodes and preharvest aflatoxin contamination in peanut. Proc. Aflatoxin Elimination Workshop p. 101. Interpretive Summary: not required
Technical Abstract: A field study was conducted to determine whether aflatoxin levels in peanut, Arachis hypogaea, were correlated with pod and root galling caused by the peanut root-knot nematode. The experiment was conducted under a rain-out shelter containing 24 cement plots (each 2 x 2 m) with the following treatments: root-knot nematodes alone (RKN), Aspergillus fiavus (Al) alone, RKN + Af, and no nematodes or fungus. Each treatment was replicated six times. Peanut seedlings, either infected with RKN or uninfected, were transplanted into half the plots. Inoculum of Af was sprinkled over the plant canopy at mid bloom. Drought was induced after pod set by covering plots during rain with a fiberglass shelter. Pod- and root-gall indices were determined for all plants in the plot and averaged. Pods from each plot were bulked, shelled, and a subsample of kernels was used to determine aflatoxin concentration and percentage colonized by Af. In this abstract, we report the results from field trials conducted in 2001 and 2002. Aflatoxin concentrations in kernels were greater in 2002 than in 2001 (1,994 vs 256 ppb; P 0.0001). Because there was no interaction between year and any of the other factors, the data for the two years were combined. In plots inoculated with Af, aflatoxin concentrations were high and were not affected by the nematode; however, in plots not inoculated with the fungus, aflatoxin concentrations were greater in the presence of nematodes. In plots without fungal inoculum, there was an increase (P < 0.04) in aflatoxin contamination of kernels with increasing root and pod galling. Pod galling accounted for 83% of the variation in aflatoxin concentration in 2001; however, the strength of the relationship with aflatoxin was much less for pod galling in 2002 and for root galling in both years (R between 0.43 and 0.57). Colonization of kernels by A. flavus increased with increasing pod galling (P = 0.04, R = 0.18) in 2001 but not in 2002. The results of this study indicate that infection of peanut by root-knot nematodes can lead to an increase in aflatoxin contamination of peanut kernels when the plants are subjected to drought stress during pod maturation. This interaction was not observed in plots where A. flavus inoculum was applied. Perhaps the high inoculum level of the A. flavus group and subsequent aflatoxin production in these plots masked the enhancing effects of the nematode.