THE NATURE OF HETEROSIS EXPRESSION IN TERMS OF VALUABLE BREEDING TRAITS IN F1 HYBRID COMBINATIONS OF WATERMELON (CITRULLUS LANATUS (THUMB.) MATSUM. ET NAKAI)

Objective. To investigate the inheritance patterns of breeding traits in 95 F1 watermelon hybrids developed from marker-assisted parental lines, focusing on the level of heterosis and the degree of dominance. Subject. 95 hybrid combinations of common watermelon developed by the Institute of Vegetable and Melon Growing of the National Academy of Agrarian Sciences of Ukraine. Methods. Measurement and weighing, statistical, and computational. Results. It was established that positive dominance and superdominance prevail in terms of yield, marketability, and fruit weight (76.2–93.9% of cases). In particular, positive superdominance in yield was detected in 89.4% of combinations. Additive gene action was less common (3.9–13.2%). A heterosis effect of 101–180% was demonstrated by 75.8% of the hybrids, while 13.3% were highly heterotic (over 180%). Stable heterosis within the range of 121–180% was observed in 68.9% of the samples. The group of the most promising genotypes (heterosis >180%) accounted for 15.9%. In terms of marketability, 70.1% of the samples had a value of 101–120%, and in terms of fruit weight, 40.2% of the hybrids demonstrated a level of 121– 180%. Forty-one best combinations with stable overdominance were identified. Since dominance is characteristic of the vast majority of hybrids, heterosis-based breeding based on these parameters is highly promising for obtaining productive watermelon varieties. Discussion. The results obtained are consistent with current global trends and confirm the effectiveness of the chosen strategy. The identified patterns of heterosis are consistent with both classical and recent genetic studies, which attests to the reliability of the methodological framework. Conclusions. A study of 95 F1 hybrid combinations of watermelon showed that yield, marketability, and fruit weight are inherited via complete dominance or superdominance (76–94%). Most genotypes (75.8%) exhibit a heterosis level of 101–180%. Assessment of the degree of dominance and the heterosis effect allowed us to determine the mode of inheritance of traits and identify 41 promising F1 combinations for further testing and introduction into production.