The physiological-thermodynamic basis for hybrid vigor (yield heterosis) in corn and other crops is not presently known. Thus, development and selection of inbred lines for hybrid vigor relies on general knowledge about heterotic groups, numerous crosses, and extensive field tests to achieve the industry average of I to 2 bu/acre/yr increase in yield. Each commercial hybrid may cost from Sl.2 to $2.5 million over an 8 to 10 year period. We propose to address this problem with a systems approach based on a combination of nondestructive, in-vivo methods utilizing the short-lived isotope tracer 1lCO2 to measure a thermodynamically complete set of physiological characteristics controlling carbon assimilation and allocation in inbred lines of corn from selected heterotic groups whose hybrids express different levels of vigor. The resulting profiles of potentially complementary physiological characteristics for each inbred line would aid in developing or selecting for desired types of combining ability. Also, by testing each plant under different environmental conditions, one can select for improved responses to drought, elevated CO2, pollutants, and other stresses. Significant correlations between these physiological characteristics and yield would enable breeders to increase number and performance of superior hybrids for a given amount of breeding and testing effort, and thus gain . competitive advantages in the market.Applications:The technology of this project has commercial potential as a service to breeders in aiding development of vigorous hybrids. Test information could help improve the efficiency of breeders' programs by: 1. Aiding in selection of combining types (parental lines); providing new information on combinability. 2. Assisting in development (through breeding or genetic engineering) of superior combining types. 3. Contributing to the understanding of certain environmentally unstable hybrids leading to corrective measures, and identifying specific hybrids for specific markets. 4. Aiding the investigation of productivity limits that may lead to larger changes in productivity with each new hybrid. 5. Aiding the selection of testers.
