|Evett, Steven - Steve|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2007
Publication Date: 7/1/2007
Citation: Balota, M., Payne, W.A., Evett, S.R., Lazar, M.D. 2007. Canopy temperature depression sampling to assess grain yield and genotypic differentiation in winter wheat. Crop Science. 47:1518-1529. Interpretive Summary: Winter wheat breeders routinely grow hundreds of varieties every year in order to find which varieties are best suited to a particular environment – that is, which ones yield the most. This is difficult and labor intensive work that takes a great deal of time. Breeders could greatly speed up the process of selecting new, higher-yielding varieties if tools were available that would allow the breeder to routinely find the better adapted varieties without having to grow them to maturity and harvest in order to find the yield. We tested a new technology for measuring crop leaf temperature to see if the measurements were well related to yield and to find out what times of day were the best for making the measurements. The new technology allowed us to set up a system to automatically measure leaf temperatures every 15 minutes throughout the season, with no one in attendance – which greatly reduced labor costs. We found that leaf temperatures measured at 9 a.m., 1 p.m. and 6 p.m. were very well related to final yield and that these leaf temperature measurements could be made several weeks before harvest. This finding allows breeders to use the new technology with reduced labor costs and allows them to more quickly determine which varieties to select, while only occasionally growing the crop out to harvest, which further reduces costs.
Technical Abstract: Canopy temperature depression (CTD = Ta - Tc) has been used to model crop yield, heat, and drought tolerance; but when to measure CTD for breeding selection has seldom been addressed. Our objective was to determine optimal measurement times in relation to growth stage, time of day, and environment. Three years of CTD and weather measurements were used to assess regression models of grain yield and stress tolerance of three wheat lines. Significant genotypic differences for CTD and grain yield were measured in all years. In dryland, long-term mean CTD at noon and yield were correlated in 2000 and 2001. The relation of short-term CTD readings to grain yield was highly variable. Poor correlation was associated with days of low solar irradiance, high wind speed, and rain events. Genotype effects on CTD were present for all hours of day and night. With few exceptions, genotype x hour interactions were insignificant at night, therefore nighttime measurements may provide more stable conditions for CTD comparison among genotypes. In general, tree regression appeared to assess grain yield and stress tolerance from short-term CTD measurements better than did linear regression and showed that the best times to measure CTD were 9 h, 13 h and 18 h. Tree regression models gave better agreement with empirical data and provided at least a heuristic interpretation of crop water status under different scenarios of soil water availability. Our results give practical guidelines on how to better use CTD in studies of genotypic yield and stress tolerance variations.