Association Mapping of Selected Drought Responsive Vegetation Indices and Agronomic Traits in Winter Wheat

Efficient and high-throughput phenotyping methods are highly sought to exploit the deluge of molecular marker information in characterizing desired agronomic traits.  The objective of this study was to evaluate the use of canopy spectral reflectance (CSR) indices for genetic characterization of drought tolerance in winter wheat. In 2011/12 growing season, a panel of 402 winter wheat cultivars, breeding lines and landraces was phenotyped under drought condition. Population structure analysis using 250 unlinked SNP markers identified three subgroups. Grain yield was significantly correlated to NDVI and NWI-I (ρ = 0.7 and -0.69 respectively, p < 0.0001) taken at milking and soft dough growth stage on the overall population. Heading date, plant height and peduncle extrusion showed significant relation to yield in some of the subgroups. Marker-trait association was analyzed for these traits using a mixed linear model that include effect of unified (Q+K) population structure. Five loci were associated with yield, 11 with NDVI, 13 with NW-I, 3 with peduncle extrusion and nine with heading date (p < 0.001). All markers associated with grain yield were also associated with either NW-I or NDVI. Synteny analysis of markers with consensus linkage map localized most of these loci on 5A, 1B and 2B chromosomes which contain significant LD for 36%, 31% and 45% of marker pairs (p < 0.001) respectively. The stability of associations and predictive power of these indices was evaluated under water sufficient growth condition. This study highlighted the importance of CSR based screening in genetic analysis and breeding efforts.