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 wheat in many parts of the world. Moreover, predictions of climatic change and water scarcity 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. In 2010, we evaluated 283 of these lines under full irrigation in Greeley, CO, for phenology, flag leaf characters (width, length, and senescence), and plant height. 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 image parameters. However, the lines were not distinguishable in most of the normalized difference vegetation index (NDVI) measurements. Phenotypic trait-based multivariate analysis also indicated the presence of large phenotypic variations among the lines.  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. Seed hardness was negatively correlated with 1000 kernel weight (-0.34) whereas seed diameter was highly correlated with 1000kernel weight (r=0.90), showing 1000 kernel weight is a good indicator of seed diameter. This preliminary study indicated the suitability of the panel for association mapping. Therefore, the study will be repeated at Colorado and Ethiopia for one more season both under wet and dry treatments.