Phenotypic Evaluation of a Spring Wheat Association Mapping Panel Targeted to Identification of Heat and Drought Tolerance Genes.

Drought is a major abiotic stress that limits productivity of staple food crops, including wheat, in many parts of the world. Moreover, predictions of climatic change and water scarcity in the future imply the need for further progress in developing drought and heat tolerant cultivars. The International Maize and Wheat Improvement Center (CIMMYT) has developed a spring wheat association mapping panel (n=294) specifically for the identification of genes and markers associated with heat and drought tolerance. The panel was selected from a larger set of 500 lines based on performance in international yield trials. In 2010, we evaluated 283 of these lines under fully irrigated conditions in Greeley, CO, for phenology, flag leaf characters (width, length, and senescence), plant height and dry biomass. Canopy reflectance index readings with a GreenSeeker instrument and digital images were taken during the vegetative stage and grain filling period. Our results showed that the lines were significantly different in phenological traits, flag leaf characters, plant height, dry biomass and an image parameter (relative greener area). However, the lines were not distinguishable in most of the normalized difference vegetation index (NDVI) measurements, except some readings obtained after heading. Phenotypic trait-based multivariate analysis also indicated the presence of large phenotypic variations among the lines. The mean range for days to heading was from 62 to 72 days. However, wide mean range was observed for plant height (43 to 82 cm).  From the correlation matrix of all traits, leaf senescence had significant negative correlations with NDVI (r=-0.39), relative greener area (r=-0.48), plant height (r=-0.46), days to heading (r=-0.34), and days to maturity (r=-0.67). The final dry biomass was significantly correlated with both NDVI (r=0.39) and relative greener area (r=0.36), indicating either the GreenSeeker or digital images might be useful for the assessment of this trait.