Combining ability of sunflower (Helianthus annuus L.) inbred lines for grain yield and physiological traits under optimum and water-stress conditions

To investigate the combining ability of sunflower (Helianthus annuus L.) inbred lines and also the inheritance of several physiological traits of this plant in normal irrigation and water-deficit-stress conditions, eight inbred lines with different drought tolerance were crossed with three cytoplasmic male sterile lines. The resulting 24 hybrids, 11 parents, and a commercial hybrid (Barzghar) as the control were evaluated in a split-plot design based on the randomized complete block design with three replications. Irrigation was applied in the main plots at two levels, normal (irrigation based on 100% water requirement) and stress (irrigation withhold after the appearance of the inflorescence), and 36 sunflower genotypes in subplots. During the growing season, chlorophyll content (Chl), relative water content (RWC), leaf water loss (LWL), early growth rate (EGR), leaf temperature (LT), and grain yield (GY) were measured. The analysis of variance showed the significant effect of water-deficit stress on Chl, RWC, LT, and GY. According to the results of the line × tester analysis, the effect of lines was significant for Chl, LWL, EGR, and GY in normal conditions, and on Chl and EGR in the water-deficit-stress conditions. In the case of the testers, there was a significant difference in Chl, EGR, and GY under normal conditions, and in LWL, EGR, and GY under stress conditions. The significant effect of lines and testers on these traits indicated a difference between their general combining ability (GCA) and the existence of additive gene effects. The interaction of line × tester was significant only for GY in normal conditions. Chl and EGR had a relatively high broad-sense and narrow-sense heritability at both conditions. The GY had also relatively high broad-sense heritability in both conditions but its narrow-sense heritability was only relatively high at the water-deficit-stress conditions. The C122 and C123 lines and the A19 tester had the highest positive GCA for GY in both conditions. The hybrid A196 × C41 in the normal conditions and A112 × C111 in the stress conditions had a positive SCA. Among the physiological traits, only LWL showed a significant correlation with GY in normal conditions. Under water-deficit-stress conditions, LWL and EGR had a positive correlation with GY, while LT showed a negative correlation with GY. In conclusion, it seems that LWL, EGR, and LT can be used to indirectly improve GY of sunflower under water-deficit stress conditions.

Combining ability of sunflower (Helianthus annuus L.) inbred lines for grain yield and physiological traits under optimum and water-stress conditions Keywords:

Gene action , Heritability , Hybrid , Line × tester