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Title: Genetic Basis for Varied Levels of Injury to Sweet Corn Hybrids from Three Cytochrome P-450 Metabolized Herbicides

item Williams, Martin

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2007
Publication Date: 5/1/2008
Citation: Pataky, J.K., Meyer, M.D., Bollman, J.D., Boerboom, C.M., Williams, M. 2008. Genetic Basis for Varied Levels of Injury to Sweet Corn Hybrids from Three Cytochrome P-450 Metabolized Herbicides. Journal of the American Society for Horticultural Science. 133:438-447.

Interpretive Summary: Potential for crop injury has limited the adoption of newer herbicide chemistry for use in sweet corn, and even for several herbicides registered for use in sweet corn, some sweet corn hybrids and inbreds can be severely injured or killed by postemergence herbicide application. Consequently, large numbers of hybrids and inbreds are screened each year for response to several herbicides, in attempt to identify sensitive germplasm. However, results are often highly variable among locations, and introduction of new hybrids, inbreds, and new herbicides, limits the useful longevity of such information. In this paper, we conducted a meta-analysis from a large multi-state trial where 152 hybrids were evaluated for response to three P450-metabolized herbicides. We tested the hypothesis that hybrids share a common genetic basis, and that genotypic class (i.e., homozygous tolerant, heterozygous, and homozygous sensitive) drives phenotypic response. Results showed that homozygous sensitive hybrids and inbreds were injured most, homozygous tolerant hybrids and inbreds were injured least, and heterozygous hybrids typically had an intermediate response to the herbicides. The value of taking this meta-analysis approach is showing that the effect of genetic condition at a single locus interacts with the environment and other factors, thus explaining varied responses among germplasm and locations. The impact of this research is that it largely explains variable crop injury results from previous research, and sheds new light on solving the herbicide sensitivity problem in sweet corn.

Technical Abstract: Some sweet corn (Zea mays L.) hybrids and inbreds can be severely injured or killed following post-emergence applications of certain P450-metabolized-herbicides. Consequently, existing hybrids are regularly evaluated for reaction to new herbicides, and new hybrids are evaluated for reactions to existing herbicides. In 2005 and 2006, the University of Wisconsin Cooperative Extension Service coordinated a multi-state, sweet corn hybrid-herbicide trial in which a total of 152 hybrids were evaluated for reactions to nicosulfuron, foramsulfuron and mesotrione in Wisconsin, Minnesota, New York, New Jersey, Delaware, Colorado, and Idaho. Responses of hybrids differed substantially within and among locations. The objective of this study was to determine if hybrids evaluated in the multi-state trials differed for the presence of a gene affecting herbicide sensitivity and to determine whether genotypic classes of hybrids (i.e., homozygous tolerant, heterozygous, and homozygous sensitive) responded differently. Based on responses of F2 progeny to nicosulfuron, foramsulfuron, and mesotrione, 95 hybrids were classified as tolerant and homozygous for a gene affecting herbicide metabolism; 47 hybrids were classified as heterozygous for a gene conditioning tolerance and one conditioning sensitivity; and 2 hybrids were classified as homozygous for a gene conditioning sensitivity. When trial mean levels of injury following applications of mesotrione, nicosulfuron, and foramsulfuron were above a minimal levels (i.e., >1%, >4% and >5% respectively), the response of the three genotypic groups of hybrids followed a consistent pattern. Homozygous sensitive hybrids were injured most severely and often were killed by the ALS-inhibiting herbicides. Heterozygous hybrids had an intermediate response that was more similar to tolerant hybrids than sensitive hybrids; however, injury to heterozygous hybrids was about 1.5 to 2 times greater and significantly (P<0.05) different from mean levels from injury to tolerant hybrids based on t-tests of group means and comparison of slopes from regressions of genotypic means on trial means. While crop injury from use of these postemergence herbicides may be affected greatly by environment and other factors, the potential for injury and the level of injury on any specific hybrid appears to be conditioned substantially by the genetic condition of the hybrid at a single locus.