Description

Abstract: The 38 lines that comprise ‘Tamspan 90’ peanut were studied for differential Aspet*llu,s flavus Links and A. parasiticus Spear growth and aflatoxin production under field and laboratory conditions. Required environmental conditions of temperature and moisture were not met for the production of sufficient aflatoxin for analytical studies in any of the three field experiments. Laboratory assays involving seed and pod inoculations with A. flavus and A. parasiticus mutants that produce norsolorinic acid (NOR), an orange-red pigmented precursor of aflatoxin, showed significant differences (P < 0.05) among lines when using immature and dried seed. Although relative NOR production, determined visually on the basis of orange-red pigment in the seed from the pod inoculations test, did not differ at P < 0.05, a three-fold difference was observed among the 38 lines. The relative ranking of the four checks showed Pronto to be the most susceptible followed by Starr, 55-437, and J-11, respectively, for production of NOR and aflatoxin. Comparing the reactions of the lines in three tests for NOR production, six lines were found constantly having low NOR production. Orange coloration in seed challenged by NOR A. flavus and A. parasiticus mutants was initially most prominent in the intercotyledonary cavity and the interfacial surface of cotyledons and testae. External fungal growth and coloration of pods did not consistently reflect seed infection. Orange coloration was consistently apparent in shells of immature pods. Mature pods varied from none to extensive, splotchy orange coloration. Visual assessments of individual seed for orange coloration, classified by color class, were highly correlated with quantity of aflatoxin and NOR as determined by HPLC (r = 0.83 and 0.95, respectively). Neither aflatoxin nor NOR were efficiently extracted from large samples (weight), and NOR was more difficult to extract from peanut seed than aflatoxin. Visual classification of seed for relative amount of aflatoxin contamination can be made successfully using A. parasiticus NOR mutants. Differentiating breeding lines to eliminate highly susceptible genotypes appears possible if laboratory assay and field performance are correlated.