GENOME-WIDE ASSOCIATION STUDIES OF DROUGHT RESISTANCE AND YIELD POTENTIAL IN WHEAT (Triticum aestivum L.) USING AGRONOMIC AND REMOTELY SENSED TRAITS
Gizaw, Shiferaw Abate
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Emerging phenotyping methods and increasingly abundant genotyping platforms have become valuable tools for the discovery and introgression of yield-positive and stress-adaptive genes into modern wheat (Triticum aestivum L.). The main goal of this research was to identify genomic regions that contribute to yield potential and drought tolerance in wheat using agronomic and remotely sensed phenotyping approaches. Phenotypic interrelations, genetic variability of yield, yield components, phenology, and spectral reflectance indices (SRIs) were evaluated in a Pacific Northwest (PNW) winter wheat diversity panel (n = 402). The SRIs showed moderate to high phenotypic correlations with grain yield (|r| = 0.27 – 0.84, p < 0.0001). Genetic variability and selection response were generally high for all traits in moist and cool rain-fed environments whereas relative selection efficiency using SRIs was highest in drought environments. A yield selection model based on multiple SRIs had predictive power (R2) ranging from 41 - 82%. Post-spike emergence stay green was also strongly correlated with SRIs (r = 0.26 – 0.76). Next, we conducted association mapping using 3,653 single nucleotide polymorphism (SNP) markers in the PNW winter wheat panel and identified 173 quantitative trait loci (QTL). Pleiotropic QTL for yield and component traits were identified on chromosomes 1A, 2A, 2B, 3B, 4B, 5A, and 6B. In addition, association mapping for three informative SRIs (normalized chlorophyll to pigment ratio index -NCPI, normalized difference vegetation index - NDVI, and normalized water index - NWI) was conducted with a North American spring wheat diversity panel (n = 250) using 19, 967 SNP markers that resulted in identification of 51 QTL on ten chromosomes including a shared QTL for yield and NDVI on chromosome 4A. The cumulative effect of multiple SRI QTL explained 9 to 16% of variation in yield whereas QTL-QTL interactions explained more than 35% of variation in yield and stress tolerance (p < 0.0001). The QTL identified in both studies will have practical use in regional and global wheat breeding for yield potential and drought tolerance. The study also highlighted the potential of using SRIs to identify novel and previously known QTL for yield and component traits in variable environments.