Genetic analysis and marker association of physiological traits under rainfed and heat stress conditions in spring wheat (Triticum aestivum L.)

Identifying gene interactions and markers associated with physiological traits, especially at later stages of grain filling, can help develop effective breeding methodology in wheat crop. Six generations (P1, P2, F1, F2, BC1P1 and BC1P2) of four different spring wheat crosses (drought-responsive x drought susceptible) and F3 generation of a single cross, i.e., MACS6272 x UP2828 were phenotyped and genotyped to decipher gene action and associated markers. Ample variation in canopy temperature depression (CTD - 2.6 - 5.6?C), chlorophyll content by SPAD (39.6 - 51.3), relative water content (RWC - 51.5 - 75.4 %), grain filling period (GFP - 61.1 - 80.1 days), 100 seed weight (3.7 - 5.5 grams), harvest index (HI - 25.8 - 46.2 %), biological yield (BY - 35.5 - 89.8 grams) and grain yield (GY - 13.4 - 36.5 grams) per plant were observed in six generations. GY positively correlated with CTD, SPAD, 100SW, BY and HI (0.08* - 0.85**). BY had the maximum direct (0.82) and indirect effect via other traits on GY. Significant non-additive epistatic interactions (j & l) and duplicate gene action were found for most traits except GFP and 100SW. Seven different SSR markers associated with CTD, SPAD, NDVI, RWC, 100SW, and explained phenotypic variation (PVE) ranging from 10.1% to 18.4%, with marker Xcfd35 explaining highest PVE for RWC. The identified candidate genes (in silico) belonged to transmembrane proteins (Xcfd32, Xcfd50), nucleic acid binding domains (Xbarc124, Xgwm484) and having enzymatic activity (Xcfd35, Xwmc47, Xwmc728) important for abiotic stress tolerance. Complex inheritance deciphered by six generations indicated delaying the selection to later stages of segregation so that useful transgressive segregants can be selected for improving grain yields in wheat.