No abstract

Fumonisins (FB) and AAL-toxin are sphingoid-like compounds produced by several species of fungi associated with plant diseases. In animal cells, both fumonisins produced by Fusarium moniliforme and AAL-toxin produced by Alternaria alternata f. sp. lycopersici inhibit ceramide synthesis, an early biochemical event in the animal diseases associated with consumption of f. moniliforme-contaminated corn. In duckweed (Lemna pausicostata Heglem. 6746), tomato plants (Lycopersicon esculentum Mill), and tobacco callus (Nicotiana fabacum cv Wisconsin), pure FB1 or AAL-toxin caused a marked elevation of phytosphingosine and sphinganine, sphingoid bases normally present in low concentrations. The relative increases were quite different in the three plant systems. Nonetheless, disruption of sphingolipid metabolism was clearly a common feature in plants exposed to FB, or AAL-toxin. Resistant varieties of tomato (AsclAsc) were much less sensitive to toxin-induced increases in free sphinganine. Because free sphingoid bases are precursors to plant "ceramides," their accumulation suggests that the primary biochemical lesion is inhibition of de novo ceramide synthesis and reacylation of free sphingoid bases. Thus, in plants the disease symptoms associated with A. alternata and F. moniliforme infection may be due to disruption of sphingolipid metabolism.

Resistance to mycotoxin contamination was compared in field samples harvested from 45 commercial corn (maize) hybrids and 5 single-cross aflatoxin-resistant germplasm lines in years with high and moderate heat stress. In high heat stress, mycotoxin levels were (4.34 +/- 0.32) x 10(3) microg/kg [(0.95-10.5 x 10(3) microg/kg] aflatoxins and 11.2 +/- 1.2 mg/kg (0-35 mg/kg) fumonisins in commercial hybrids and 370 +/- 88 microg/kg (140-609 microg/kg) aflatoxins and 4.0 +/- 1.3 mg/kg (1.7-7.8 mg/kg) fumonisins in aflatoxin-resistant germplasm lines. Deoxynivalenol was detected (one-fourth of the samples, 0-1.5 mg/kg), but not zearalenone. In moderate heat stress, mycotoxin levels were 6.2 +/- 1.6 microg/kg (0-30.4 microg/kg) aflatoxins and 2.5 +/- 0.2 mg/kg (0.5-4.8 mg/kg) fumonisins in commercial hybrids and 1.6 +/- 0.7 microg/kg (0-7 microg/kg) aflatoxins and 1.2 +/- 0.2 mg/kg (0.5-3.0 mg/kg) fumonisins in aflatoxin-resistant germplasm lines. The results are consistent with heat stress playing an important role in the susceptibility of corn to both aflatoxin and fumonisin contamination, with significant reductions of both aflatoxins and fumonisins in aflatoxin-resistant germplasm lines.

Information on the effects of management practices on soybean seed composition is scarce. Therefore, the objective of this research was to investigate the effects of planting date (PD) and seeding rate (SR) on seed composition (protein, oil, fatty acids, and sugars) and seed minerals (B, P, and Fe) in soybean grown in two row-types (RTs) on the Mississippi Delta region of the Midsouth USA. Two field experiments were conducted in 2009 and 2010 on Sharkey clay and Beulah fine sandy loam soil at Stoneville, MS, USA, under irrigated conditions. Soybean were grown in 102 cm single-rows and 25 cm twin-rows in 102 cm centers at SRs of 20, 30, 40, and 50 seeds m-2. The results showed that in May and June planting, protein, glucose, P, and B concentrations increased with increased SR, but at the highest SRs (40 and 50 seeds m-2), the concentrations remained constant or declined. Palmitic, stearic, and linoleic acid concentrations were the least responsive to SR increases. Early planting resulted in higher oil, oleic acid, sucrose, B, and P on both single and twin-rows. Late planting resulted in higher protein and linolenic acid, but lower oleic acid and oil concentrations. The changes in seed constituents could be due to changes in environmental factors (drought and temperature), and nutrient accumulation in seeds and leaves. The increase of stachyose sugar in 2010 may be due to a drier year and high temperature in 2010 compared to 2009; suggesting the possible role of stachyose as an environmental stress compound. Our research demonstrated that PD, SR, and RT altered some seed constituents, but the level of alteration in each year dependent on environmental factors such as drought and temperature. This information benefits growers and breeders for considering agronomic practices to select for soybean seed nutritional qualities under drought and high heat conditions.

No abstract

The veA gene positively regulates sterigmatocystin production in Aspergillus nidulans and aflatoxin production in A. parasiticus and A. flavus. Whether veA homologs have a role in regulating secondary metabolism in other fungal genera is unknown. In this study, we examined the role of the veA homolog, FvVE1, on production of two mycotoxin families, fumonisins and fusarins, in the important corn pathogen F. verticillioides. We found that FvVE1 deletion completely suppressed fumonisin production on two natural substrates, corn and rice. Furthermore, our results revealed that FvVE1 is necessary for the expression of the pathway-specific regulatory gene FUM21 and structural genes in the fumonisin biosynthetic gene (FUM) cluster. FvVE1 deletion also blocked production of fusarins. The effects of FvVE1 deletion on the production of these toxins were found to be the same in two separate mating types. Our results strongly suggest that FvVE1 play an important role in regulating mycotoxin production in F. verticillioides.

No abstract

Biological control of toxigenic Aspergillus flavus in maize through competitive displacement by non-aflatoxigenic strains was evaluated in a series of field studies. Four sets of experiments were conducted between 2007 and 2009 to assess the competitiveness of non-aflatoxigenic strains when challenged against toxigenic strains using a pin-bar inoculation technique. In three sets of experiments the non-aflatoxigenic strain K49 effectively displaced toxigenic strains at various concentrations or combinations. The fourth study compared the relative competitiveness of three non-aflatoxigenic strains (K49, NRRL 21882 from Afla-Guard®, and AF36) when challenged on maize against two aflatoxin- and cyclopiazonic acid (CPA)-producing strains (K54 and F3W4). These studies indicate that K49 and NRRL 21882 are superior to AF36 in reducing total aflatoxin contamination. Neither K49 nor NRRL 21882 produce CPA and when challenged with K54 and F3W4, CPA and aflatoxins were reduced by 84-97% and 83-98%, respectively. In contrast, AF36 reduced aflatoxins by 20% with F3W4 and 93% with K54 and showed no reduction in CPA with F3W4 and only a 62% reduction in CPA with K54. Because AF36 produces CPA, high levels of CPA accumulate when maize is inoculated with AF36 alone or in combination with F3W4 or K54. These results indicate that K49 may be equally effective as NRRL 21882 in reducing both aflatoxins and CPA in maize.