Screening of Sunflower Genotypes for Various Physiological, Agronomical and Oil Traits under Heat Stress Condition

The present study evaluated 40 sunflower genotypes under heat stress and non-stress conditions to identify tolerant genotypes for genetic improvement. Analysis of variance showed significant differences among genotypes, treatments, and their interactions for all studied traits, including germination, flowering and maturity days, plant height, head diameter, stem girth, leaf area, 100-seed weight, seeds per head, grain yield, oil and protein content, head inclination, and cell membrane stability. Under heat stress, genotypes HO-1, Vulgar, PSF-025, and Mehran exhibited the highest germination (63.66–75.33%), whereas Irani-II, A-2, Ausi Gold, and Euroflower had the lowest (48–53%). Days to 75% flowering were longest in HO-1 and PSF-025, and shortest in Turkish, Euroflower, and AS-2017. Heat stress reduced plant height, head diameter, stem girth, and leaf area, with maximum decreases observed in TJ-1 (14.01%), Irani-I (22.01%), Irani-II (48.24%), and Turkish (44%), respectively. HO-1, Peshawar-93, A-1, and TJ-1 had the highest 100-seed weight (5.00–7.00 g), while Aguara, Euroflower, and JTs-2 were lowest. HO-1 also recorded the highest number of seeds per head and grain yield per plot, whereas A-2, S-278, and D-6 were lowest. Head inclination was highest in S-278 and N-17, and lowest in HO-1 and Peshawar-93. Heat stress decreased oil and protein content, with HO-1, Peshawar-93, and TJ-1 maintaining the highest levels. Cell membrane stability was highest in A-1 and TJ-1 and lowest in FMC-0046 and NK-Rocky. Overall, heat stress caused moderate reductions in germination (2.58%), flowering (2.65%), plant height (2.47%), leaf area (7.53%), 100-seed weight (9.32%), seeds per head (8.55%), oil content (1.18%), protein content (1.87%), cell membrane stability (0.24%), and grain yield (5.19%). Genotypes HO-1, PSF-025, Peshawar-93, and TJ-1 consistently exhibited superior performance under stress and are potential candidates for breeding heat-tolerant sunflower varieties.