Effect of inoculum concentrations of Aspergillus flavus and A-parasiticus on aflatoxin accumulation and kernel infection in resistant and susceptible maize hybrids

Over a 3-years period, we compared aflatoxin accumulation and kernel infection in maize hybrids inoculated with six inoculum concentrations of Aspergillus flavus isolate NRRL 3357 or A. parasiticus isolate NRRL 6111 which is a norsolorinic acid producer. Aflatoxin resistant and susceptible maize hybrids were inoculated with six conidial concentrations (ranging from 1 x 10(3) to 1 x 10(8)/ml) of either A. flavus or A. parasiticus using the side-needle technique 7 days after midsilk (50 % of the plants had silks emerged). Aspergillus kernel infection and aflatoxin contamination was determined at ca. 63 days after midsilk. For each hybrid, aflatoxin levels were very similar regardless of the inoculum concentration. With the exception of the A. parasiticus treatments in 2007, the lowest inoculum conidial concentration (1 x 10(3)/ml) for both fungal species was sufficient to produce statistical differences between the resistant and the susceptible maize hybrids for aflatoxin contamination. There was more variability in kernel infection between inoculum concentrations than that observed in aflatoxin accumulation. Since our aflatoxin evaluations are conducted in a warm, humid environment, putting less disease pressure on plants via lower inoculum concentrations may make it possible to identify genotypes that have moderate levels of resistance to aflatoxin accumulation.