No abstract

Corn (Zea mays L.) planting dates are regional and vary across the contiguous USA. Improved technologies allow corn to be planted earlier. The objective of this research was to evaluate the effects of planting date on the agronomics of Bt and non‐Bt hybrids grown in the Mid‐South. Twelve hybrids, two Bt [Bacillus thuringiensis (Berliner)], and two non‐Bt for three maturity groups [short‐season (1180–1270 GDU 10's), mid‐season (1445–1470 GDU 10's), and full‐season (1540–1625 GDU 10's)] were evaluated for GDU 10's at silking and physiological maturity, yield, yield components, and mycotoxins in 2002, 2003, and 2004 at Stoneville, MS. Plots were planted in a split‐plot of a randomized complete block replicated four times and furrow irrigated. Whole plots were plantings in early April, late April, or mid‐May, while subplots were hybrids randomly assigned. Experimental units were four 102‐cm rows, 9.1 m long. Lodging and dropped ears were inconsequential. Yields were greater for both April plantings (8.6 and 9.2 Mg ha−1 for early April and late April, respectively) than mid‐May plantings (7.8 Mg ha−1). Short‐season hybrids generally yielded less than mid‐season or full‐season hybrids. The Bt hybrids yielded more than non‐Bt hybrids (9.1 Mg ha−1 vs. 7.9 Mg ha−1, respectively). Yields correlated with GDU 10's at silking [yield = 0.037x − 20.416 (r = 0.77)] but not physiological maturity. Aflatoxin was high in 2002 (224.0 mg Mg−1), and much less (28.8 and 7.4 mg Mg−1) in 2003 and 2004, respectively. The Bt hybrids had less fumonisin contamination than non‐Bt hybrids (5.2 mg kg−1 vs. 8.5 mg kg−1) but less aflatoxin only in 2003 (12.4 mg Mg−1 vs. 45.3 mg Mg−1).

Samples of wheat naturally infected by Fusarium graminearum Schwabe were obtained from mills in Oklahoma, Missouri, Kansas, and Minnesota and fields in Nebraska and Kansas in 1982; they were analyzed for deoxynivalenol (DON). The wheat was milled, and DON was found throughout all the milling fractions (bran, shorts, reduction flour, and break flour). The DON recoveries for each mill run ranged from 90 to 98%. These samples, regardless of DON concentration, also gave similar fractional distributions of DON. The greatest (21 ppm [21 ,ug/g]) concentration of DON was found in the bran, and the smallest (1 ppm) was found in the break flour. Cleaning and milling were not effective in removing DON; DON was not destroyed in the bread baked from the naturally contaminated whole wheat flour, but the effect on its concentration in the samples analyzed varied, the reduction ranging from 19 to 69%. The percent reduction found in the cleaned wheat ranged from 6 to 19%. DON concentrations in the following commercially made breads, caraway rye, seedless rye, and pumpernickel, were 45 ppb (ng/g), 39 ppb, and 0 ppb, respectively. The limits of detection by gas chromatography-mass spectrometry and high-pressure liquid chromatography for DON were 0.5 and 10 ng, respectively.

Of 88 isolates of Fusarium graminearum collected from soil or cereals in the United States, 49 produced 15-acetyldeoxynivalenol (15-ADON) as the major isomer; one produced 3-acetyldeoxynivalenol (3-ADON). A total of 26 isolates collected from cereals or soil in Australia, New Zealand, Norway, China, and Poland were used for comparison. Of these, 15 produced 3-ADON as the major isomer and 2 produced 15-ADON.

Thirty-nine isolates of fungi obtained from foodstuffs and soil samples from various parts of the world have been identified. The isolates were grown on a solid rice medium, and extracts were prepared with 50% aqueous methanol. The extracts were examined for toxicity in the following systems: (i) cytotoxicity to cultured normal human diploid skin fibroblasts (proliferating and nonproliferating) and mouse fibroblasts; (ii) skin toxicity after topical application on rats; and (iii) rat feeding tests in which rats were examined for death, overt pathological effects including congestion and hemorrhage of tissues, weight loss, food refusal, and uterine growth. Sixteen culture extracts were highly toxic as indicated by death, congestion and hemorrhage of tissues, and net weight loss. One half of the isolates were highly cytotoxic (50% lethal concentration, 0.01 to 5 ,ug/ml) as indicated by the ability to cause death and disintegration of 3T3 Swiss mouse fibroblasts and human diploid skin fibroblasts during 3 to 4 days in culture. The remainder were moderately cytotoxic (50% lethal concentration, 5 to 250 ,ug/ml). Four culture extracts were highly toxic by some clinical criteria but did not cause congestion and hemorrhage of tissues and were weakly cytotoxic (50% lethal concentration, 250 to 5,000 jig/ml). Six culture extracts exhibited moderate toxicity (weight loss only) and low cytotoxicity (50% lethal concentration, 3,000 to 50,000 ,ug/ml). Four culture extracts caused uterine enlargement as the major clinical sign, suggesting the presence of zearalenone. Eleven culture extracts were weakly cytotoxic and caused no major clinical signs, except skin toxicity in two extracts. Cytotoxicity values of fungal extracts obtained with cultured cells, the simplest and least expensive assay used in this study, correlated well with weight loss and food refusal observed in rat feeding studies, but not with skin toxicity or uterine growth. Extracts of several fungal isolates inhibited cell proliferation without killing cells, a characteristic not observed with any identified toxin studied in this laboratory.