Infection of maize, Zea mays L., kernels by Aspergillus flavus Link ex Fr. and subsequent aflatoxin production can be an extremely serious problem; especially in maize grown in the southeastern part of the USA. Maize genotypes that resist attack by this fungus are desperately needed. The objective of these studies was to identify maize inbreds with resistance to kernel infection by A. flavus. Inbreds were inoculated with a pinbar and evaluated for percentage of kernels internally infected by this fungus. Nearly a 5‐fold difference (6 to 30%) among the inbreds tested over a 2‐yr period was found. Five of the inbreds selected as resistant, and five as susceptible, were subsequently tested using a pinbar and two needle inoculation techniques. The pinbar inoculation technique gave the highest level of kernel infection and the greatest separation of the inbreds into their previously classified groups, but all methods of inoculation showed that the two groups of inbreds differed significantly from each other. In a test with 50 inbreds inoculated by the side‐needle inoculation technique, percentage of A. flavus infected kernels ranged from 4 to 62. Resistant (Mp313E, SC54, and Mo18W) and susceptible (T202, T216, and SC212M) inbreds averaged 10 and 44% infected kernels, respectively.

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The seriousness of a disease is reflected in the amount of yield reduction caused by the disease under field conditions. We wished to obtain data on the amount of yield loss of corn (Zea mays L.) caused by the corn stunt disease complex which includes the maize chlorotic dwarf virus (also referred to as Ohio corn stunt agent) and the Mississippi corn stunt agent, believed to be a mycoplasma; and to determine if time of initial disease symptoms influences the amount of yield reduction. Corn hybrids were subjected to natural infection under field conditions during 5 years. Plants showing disease symptoms were tagged and yields from these plants were compared with plants not showing disease symptoms. Yields from diseased plants were less than 50% of those from healthy plants in each of the 5 years. The number of ears and kernels per plant was reduced more than was the weight of kernels on the diseased plants. Plants showing disease symptoms early in the season were more severely affected than plants that developed symptoms later. From our data, we concluded the following: diseased plants showing symptoms as early as 52 days after planting would produce no grain; plants showing first symptoms as late as 107 days after planting would produce normal yield; between the two extremes the yields on diseased plants would be reduced by 1.82% of that on healthy plants for each day the first symptoms appeared earlier than 107 days after planting.