The climate is continuously changing, consequently increasing the drought-affected areas. As such, it challenges breeders to develop adaptive and drought-tolerant sunflower (Helianthus annuus L.) cultivars through evaluation and inducing genes tolerant to drought. Hence, the recent study aimed to assess the sunflower hybrids during 2019–2020 under well-watered and stressed conditions in a splitplot design with four replications at the Sindh Agriculture University, Tandojam, Pakistan. The observed data determined heterotic effects among 15 F₁ hybrids for days to 75% flowering, days to 75% maturity, stem diameter, head diameter, biological yield plant^-1, seeds head^-1, seed index, and seed yield plant^-1. The mean squares due to genotypes, treatments, and genotype by treatment were significant for all the traits, which exhibited that genotypes performed significantly across the environments for the above-cited traits. The F₁ hybrids, such as, Mehran × Pehawar-93, gave maximum negative heterotic effects for phonological traits which will benefit the development of short-duration sunflower hybrids. Further, F₁ hybrids like Thatta × UC-666 displayed higher heterotic effects for head diameter, stem diameter, number of seeds plant^-1, seed index, and biological plant^-1 and PSF-025 × B2 and HO.1 × B2 gave higher heterotic effects for the number of seeds head^-1 and seed yield plant^-1 under stress environment.

Keywords: Sunflower (Helianthus annuus L.), split-plot design, well-watered and stressed-conditions, heterosis, heterobeltiosis, yield-related traits

Key findings: Four sunflower (Helianthus annuus L.) hybrids, Mehran × Peshawar-93, Thatta × UC-666, PSF 025 × B-2, and HO-1 × B-2 showed promising that could benefit future breeding programs for hybrid crop development.