Contamination of sesame seed grown in Mississippi with aflatoxin, fumonisin, and mycotoxin-producing fungi

Four sesame varieties (S-34, S-35, S-38, and S-39) were planted in the Mississippi Delta in 2014 and 2015 at four nitrogen fertiliser application rates from 44.8 to 112 kg N/ha, and evaluated for grain yield and contamination by mycotoxins and toxigenic fungi. Variety S-35 had the highest yield in both years. Harvest seed moisture was not related to variety, because opposite results were obtained in the two years. N fertiliser application rate had no effect on yield or mycotoxin contamination of harvested seed in 2014, but significantly increased yield in 2015. Harvested sesame seed density was influenced by treatments (N rates and variety) with varietal differences occurring in the different years. While observed differences were small, even small differences could impact marketability. There was no significant effect of N fertiliser application rate, variety, crop year or interaction between them for contamination of harvested seed by aflatoxins, fumonisins, Aspergillus flavus or Fusarium verticillioides in cleaned and uncleaned harvested sesame seed. Similar results were obtained from trials conducted in the Florida Panhandle during 2015. In general, sesame seed is not susceptible to aflatoxin and fumonisin contamination. None of the mycotoxin levels observed in this study were significant in regard to human or animal health, but further testing is needed. This is the first report of fumonisin found in sesame seed. The results of this study indicate that sesame seed is a safe crop for growers and consumers.

Seasonal Progress of Charcoal Rot and Its Impact on Soybean Productivity

The seasonal progress of charcoal rot (caused by Macrophomina phaseolina) was measured over two growing seasons in four separate experiments: irrigated infested, irrigated non-infested, non-irrigated infested, and non-irrigated noninfested. Disease was assessed at V5, R1, R3, R5, R6, and R7 growth stages based on colony forming units (CFU) of M. phaseolina recovered from the lower stem and root tissues and the area under the disease progress curve (AUDPC). The population density of M. phaseolina increased slowly from the V5 to R6 growth stages and then rapidly from the R6 to R7 growth stages for all genotypes in all four experiments. Yield loss due to charcoal rot ranged from 6 to 33% in irrigated environments. The extent of yield loss was affected by severity of charcoal rot, which in turn was affected by year. Yield loss due to charcoal rot was consistently measured in all paired comparisons in irrigated environments, suggesting that charcoal rot can be an important disease in irrigated environments. Disease severity based on CFU accounted for more yield loss variation (42%) than did the AUDPC (36%) when used to assess disease. Growth stage R7 was found to be the optimum stage for assessing disease using CFU. In addition, screening soybean genotypes under irrigation environment may have utility in breeding programs where there is a need for evaluating soybean genotypes for both disease resistance and yield.

Transgenically enhanced sorbitol synthesis facilitates phloem boron transport and increases tolerance of tobacco to boron deficiency

The mobility of elements within plants contributes to a plant species' tolerance of nutrient deficiencies in the soil. The genetic manipulation of within-plant nutrient movement may therefore provide a means to enhance plant growth under conditions of variable soil nutrient availability. In these experiments tobacco (Nicotiana tabacum) was engineered to synthesize sorbitol, and the resultant effect on phloem mobility of boron (B) was determined. In contrast to wild-type tobacco, transgenic tobacco plants containing sorbitol exhibit a marked increase in within-plant B mobility and a resultant increase in plant growth and yield when grown with limited or interrupted soil B supply. Growth of transgenic tobacco could be maintained by reutilization of B present in mature tissues or from B supplied as a foliar application to mature leaves. In contrast, B present in mature leaves of control tobacco lines could not be used to provide the B requirements for new plant growth. 10B-labeling experiments verified that B is phloem mobile in transgenic tobacco but is immobile in control lines. These results demonstrate that the transgenic enhancement of within-plant nutrient mobility is a viable approach to improve plant tolerance of nutrient stress.