Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/24/2008
Publication Date: 12/1/2008
Citation: Williams, M., Wax, L.M., Pataky, J.K., Meyer, M.D. 2008. Further Evidence of a Genetic Basis for Varied Levels of Injury to Sweet Corn Hybrids from Cytochrome P450-Metabolized Herbicides Applied Postemergence . HortScience. 43:2093-2097. Interpretive Summary: Since certain sweet corn hybrids are sensitive to postemergence herbicides, new hybrids are frequently screened for responses to existing herbicides, and new herbicides are routinely tested for potential injury to existing hybrids. Alleles at a single cytochrome P450 locus condition response of corn to multiple, P450-metabolized herbicides, including: carfentrazone, foramsulfuron, halosulfuron, mesotrione, nicosulfuron, and tembotrione. Since 2002, 249 to 379 sweet corn hybrids were evaluated annually for responses to the aformentioned postemergence herbicides at Urbana, Illinois. Analysis of these data showed that variation in levels of injury observed in sweet corn hybrid nurseries was associated with the genotypes of hybrids at a locus conditioning herbicide cross-sensitivity, presumably the Nsf1/Ben1 locus. Homozygous tolerant hybrids were injured the least, homozygous sensitive hybrids were injured the most, and injury to heterozygous hybrids was intermediate to the other two genotypic classes or similar to homozygous tolerant hybrids. These results help explain the lack of perfect association between hybrid responses in previous research. While other factors (e.g. environmental) also influence level of crop injury, probability of crop injury from P450-metabolized herbicides is largely influenced by alleles at a locus conditioning herbicide cross-sensitivity.
Technical Abstract: Over the last two decades, sweet corn injury from postemergence herbicides has resulted in routine screening of combinations of new and existing hybrids and herbicides. Sensitivity of sweet corn to several cytochrome P450-metabolized herbicides is simply inherited and has a common genetic basis, a single P450 locus which may account for a large amount of the variation in sweet corn injury commonly observed among screening trials. Using data from 13 hybrid-herbicide screening trials conducted over six years, the objective of this work was to determine if variation in levels of injury from P450-metabolized herbicides was associated with the genotypes of hybrids at a locus affecting herbicide sensitivity and tolerance. Of the 703 hybrids evaluated in the University of Illinois sweet corn hybrid nurseries from 2002 to 2007, previous work showed that a total of 104, 70, and nine of the hybrids were known to be homozygous tolerant, heterozygous, or homozygous sensitive for an allele affecting herbicide response. Nurseries from 2002 to 2007 included six trials with mesotrione, three trials with nicosulfuron, and one trial each with foramsulfuron, tembotrione, halosulfuron, and carfentrazone. When means of hybrids in genotypic classes were compared, homozygous sensitive hybrids were consistently injured more severely than homozygous tolerant and heterozygous hybrids. When trial mean levels of injury exceeded 2%, heterozygous hybrids had an intermediate response that was closer to homozygous tolerant hybrids than homozygous sensitive hybrids. These data are further evidence that the probability of injury from several P450-metabolized herbicides including mesotrione, nicosulfuron, foramsulfuron, tembotrione, halosulfuron, and carfentrazone, is highest in homozygous sensitive hybrids and least in homozygous tolerant hybrids, and that variability of responses of sweet corn to these P450-metabolized herbicides can be explained largely by the genotype of a hybrid at a single locus.