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Normal and opaque‐2 endosperm counterparts of two Zea maysL. hybrids were grown during 1973 at locations in Illinois, Missouri, Georgia, and Texas; 20 days after silking test ears were inoculated with Aspergillus flavusLink ex Fr. spores. Other ears were mechanically damaged or untreated. Sample ears were harvested 15, 30, 45, and 70 days after treatment. After shelling the corn was ground, examined for bright‐greenish yellow (BGY) fluorescence, and assayed for aflatoxin. The number of aflatoxin‐positives in 128 inoculated ears/plot increased generally from North to South: Illinois, 28; Missouri, 86; Texas, 111; and Georgia, 117. The mean levels of aflatoxin B1in toxin‐contaminated ears showed a similar geographical pattern: Illinois, 2.4 ppb; Missouri, 22.5 ppb; Texas, 114.5 ppb; and Georgia, 133.9 ppb. Almost all the toxin production occurred during the initial 30 days after inoculation. Fewer toxin‐contaminated ears were found in the doublecross hybrid than in the single cross, but no significant difference in aflatoxin incidence was observed between endosperm types (normal vs. opaque). Sixty of 512 damaged uninoenlated ears and 21 of 512 untreated control ears contained aflatoxin; 80% of the aflatoxin‐positives associated with physically damaged or control ears were observed in corn from the Georgia location.

Phomopsis seed decay (PSD) reduces soybean [Glyclne max(L.) Merr.] seed quality and seedling establishment. Experiments were conducted in Columbia, MO, and Isabela, PR, over a 3‐yr period to identify a source(s) of resistance to PSD in soybean. All genotypes evaluated were field grown under conditions favorable for infection by Phomopsisspp. Percentage infection was determined by counting colonies of Phomopsisspp. growing from surface‐sterilized seeds plated on acidified potato (Solanumspp.) dextrose agar. Plant introduction (PI) 417479 was free of Phomopsisspp. seed infection at Columbia in 1984 and Isabela in 1985, and had 3% infection at Columbia in 1985. A phenotypically indistinguishable genotype, PI 360841, had levels of infection that did not differ statistically from those observed for PI 417479 and may be a duplicate in the germplasm collection. In the same environments, the widely grown ‘Williams 82’ showed from 25 to 59% infection. The PI 417479 exhibited less infection than the reported P. sojaeLehman resistant genotypes PI 80837 and ‘Delmar’ in all but one test. Maturity dates of PI 417479 were near the average of all genotypes tested. The PI 417479 appears to have been exposed to average, or above average, disease pressure. Thus, the level of resistance to PSD measured cannot be attributed to maturation during periods of favorable environmental conditions. Also, antagonism of Phomopsisspp. seed infection by Cercospora kikuchii(T. Matsu. & Tomoyasu) Gardner did not appear to influence the conclusions relative to PI 417479. Detectable seed infection of PI 417479 by C. kikuchiiwas 2% or less in all experiments.

Twelve corn (Zea maysL.) hybrids, including one reciprocal, with differences in trypsin inhibitor levels and insect resistance were grown during 1978 at 12 locations in the United States. The study examined the effect of planting date, inoculation with Aspergillus flavusLink ex Fr., and mechanical damage of developing kernels on aflatoxin accumulation in kernels before harvest. Although a broad occurrence of toxin was found in kernels of untreated ears from locations outside the Corn Belt, addition of A. flavusspores to silks markedly increased toxin accumulation. To a lesser extent, mechanical damage was also associated with elevated aflatoxin concert. trations. At specific locations, toxin levels varied among hybrids, but no consistent interlocation pattern of absolute toxin resistance was detected. Visual insect damage on mature ears was not linked quantitatively to toxin levels. More than 90% of the Georgia, Mississippi, Missouri, North Carolina, South Carolina, and Tennessee samples had detectable aflatoxin, but less than 30% of the samples from Illinois, Iowa, and Ohio were toxin positive. In general, bright greenish‐yellow (BGY) fluores. cence in kernels and high levels of toxin were observed, but a number of samples with low levels of toxin did not exhibit the fluorescence.