A MULTI-PARAMETER EVALUATION OF DROUGHT TOLERANCE IN SUNFLOWER HYBRIDS BY IDENTIFICATION OF SUPERIOR GENOTYPES AND SELECTION CRITERIA FOR BREEDING PROGRAMME

Abstract

Drought stress remains a critical barrier to sunflower productivity under changing climate conditions. This study employed both pot and field trials to evaluate drought tolerance mechanisms in eight sunflower hybrids through morphological, physiological, and yield assessments. The moisture stress significantly reduced plant height (8.6%), SPAD chlorophyll content (7.0%), and stem girth (10.5%) (p < 0.05), with seed yield showing the greatest decline (37.3%, p < 0.001). Physiological responses revealed complex water-use strategies: photosynthetic rates were minimally affected (4.1% decline, non-significant), while water use efficiency decreased markedly (18.9%), a response attributed to elevated transpiration measured under acute stress conditions (before watering). Stomatal conductance increased by 33% under stress. The increase in stomatal conductance is consistent with an isohydric-to-anisohydric regulatory shift observed during recovery phases following rewatering in tolerant sunflower genotypes. Principal component analysis, explaining 61.1% of the variation, enabled classification of hybrids into stress-tolerant (RSFH-1, KBSH-53), moderately tolerant (KBSH-41, KBSH-44), and stress-sensitive (DRSH-1, KBSH-42, PAC-3794, RSFH-130) groups. A strong negative correlation (r = –0.84, p < 0.001) between yield decline and photosynthetic maintenance identified photosynthetic resilience as a key breeding trait. Moderate agreement between pot and field trials (r = 0.217) underscored the need for multi-environment validation. Superior genotypes RSFH-1 and KBSH-53 demonstrated stable performance across stress indicators, offering immediate value for deployment and breeding. This multi-parameter framework provides a robust strategy for breeding climate-resilient sunflower cultivars.