Submitted to: Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 7, 2013
Publication Date: February 7, 2013
Citation: Dowd, P.F. 2013. Corn and sorghum studies by the usda "Ag Lab" in 2012. Workshop Proceedings. xx. Technical Abstract: Studies again included several popcorn fields in 2012. The research has been redirected to investigate environmental influences on gene expression directly and indirectly involved in resistance to mycotoxin production, so milk stage undamaged and damaged ears have been saved in the freezer for the gene expression analysis as well. Weather conditions were much hotter and drier than normal in 2012. The three years of collections have been from years very different in weather conditions and mycotoxin production, so should yield good comparative data. RNA has been extracted, cDNA made, and hybridizations started. Damage by caterpillars was variable, but appeared to depend on planting date, as ears of late planted corn had much higher levels of damage by European corn borers. There was some damage by corn earworms and Western bean cutworms, but it was not common. Spraying for Japanese beetles may have helped reduce European corn borer damage in early planted corn as well. Stink bug and sap beetle damage was much less common than normal. Some visible Aspergillus flavus (the mold that makes aflatoxin) was found in some fields. Although aflatoxin was detected in nearly every insect damaged sample, overall levels were well below 20 ppb, the FDA regulatory threshold. Some insect damaged kernels were visibly molded by Fusarium. As is usually the case, ears with greater levels of insect damage had higher levels of fumonisin, but it was below levels for concern. Low levels of DON were found in most fields, and did not appear to be associated with insect damage. New funding from the National Institute of Food and Agriculture has permitted experiments to be set up to evaluate insect damage to low lignin lines of sorghum, which are also being examined for bioenergy production. Greenhouse and plant growth room studies have generally indicated no significant increase in susceptibility of leaves to corn earworm or fall armyworm damage in the low lignin lines, and greatly enhanced pith resistance to these species. When grown at the Havana research site, the incidence of leaf damage was often similar for bmr6 and normal lignin line, but higher for the bmr12 versus normal lignin line. The amount of leaf damage was significantly less at times, especially for the bmr6 line. European corn borer stalk damage incidence was similar for all three sorghum lines examined, but the amount of stalk boring was significantly lower in the bmr6 and bmr12 stalks compared to the normal lignin stalks. These results are similar to results for assays where leaves or pith has been removed for lab or small plot grown plants and fed to corn earworm and fall armyworm larvae, as the bmr6 leaves have had less damage and pith has been more toxic to both species.