Variations in morphological and physiological traits of bread wheat diallel crosses under timely and late sowing conditions

Four wheat cultivars and their F1 hybrids, at full diallel design, were sown timely and late to represent non-stress and stress conditions. The objectives of this study were to (1) investigate gas exchange (An, gs, Ci, An/Ci), canopy temperature depression (CTD), chlorophyll content measured by SPAD-502 chlorophyll meter (SPAD, soil plant analysis development) and certain agronomic traits, (2) to determine the relationships among all traits, and (3) to obtain genetic information on physiological traits via diallel analysis. Gas exchange at the medium milk development stage and SPAD measurements at the heading and late milk development stages were made on flag leaf. CTD was measured at medium milk development at three different times of day: late morning, noon and early afternoon.All gas exchange parameters decreased under late sowing conditions, except An/Ci. The CTD was higher under the late sowing conditions compared with the timely sowing conditions. The plants were cooler at early afternoon than at the other measurement times. The SPAD chlorophyll at the heading time for timely sowing was higher than for late sowing, while the SPAD chlorophyll at the late milky stage decreased for timely sowing and increased for late sowing with respect to the measurement at heading time.Compared with the parents, the hybrids had higher values for grain yield, CTD, SPAD chlorophyll and all agronomic traits under both conditions. Significant reciprocal differences were observed in all gas exchange parameters (under both non-stress and stress conditions), except for Ci under non-stress conditions, while reciprocal effects were not observed for SPAD chlorophyll. Reciprocal effects for CTD were significant at noon and early afternoon under stress conditions. SPAD chlorophyll at heading and late milk development correlated significantly with grain yield under stress conditions. All CTD and SPAD chlorophyll measurements showed corresponding correlations with grain yield under non-stress conditions. The data indicate that SPAD chlorophyll has the potential, as an indirect selection criterion in early segregating generations, to improve high grain-yielding genotypes under stress conditions.

► We evaluated physiological traits as possible selection criteria in wheat under heat stress.
► Diallel hybrids of 4 wheat parents had higher values for all traits under non- and stress conditions.
► No reciprocal effects were observed for SPAD chlorophyll.
► SPAD chlorophyll at early grain development correlated with yield under non- and stress conditions.
► SPAD chlorophyll can be reliably used to select high yielding lines for heat stressed conditions.