Tomato (Solanum lycopersicum L.) is one of the most important horticultural crops worldwide, with yield and fruit quality strongly constrained by biotic stresses, particularly tomato yellow leaf curl virus (TYLCV). Hybrid breeding through the exploitation of heterosis is a highly effective approach for improving yield, fruit quality, and TYLCV resistance. To investigate the genetic basis of heterosis and trait inheritance, 17 determinate female and 7 semi-determinate male inbred lines were crossed in a North Carolina Design II (NCII) scheme, generating 119 F₁ hybrids evaluated alongside their parents and control cultivars. To ensure uniform and consistent TYLCV infection pressure, the highly susceptible cultivar ‘Matin’ was interplanted throughout the field as a spreader genotype. Heterosis analysis revealed substantial positive better-parent heterosis (BPH) for yield-related traits, particularly single-plant yield and fruit number per plant, whereas negative heterosis was favorable for traits such as sunscald incidence, fruit acidity, and TYLCV severity. Genetic variance partitioning indicated that reproductive traits such as number of inflorescences on the main stem (NIMS), number of flowers per inflorescence (NFI), and number of fruits per inflorescence (NFPI) were predominantly governed by additive effects, suggesting that parental selection can efficiently improve these traits. In contrast, TYLCV resistance was strongly influenced by non-additive variance, highlighting the critical role of specific combining ability and hybrid interactions. Several hybrids combined high yield with complete resistance to TYLCV, underscoring the potential for simultaneous improvement of productivity and resilience. This study not only clarifies the genetic basis of heterosis in tomato but also identifies elite parental lines and superior hybrids that can serve as valuable resources for breeding programs aimed at developing resilient, high-yielding cultivars under biotic and climatic stress conditions.
Hatamifard et al. (Thu,) studied this question.