Gene action and hybrid vigour for yield, yield components and tolerance to the Two-Spotted Spider mite in summer squash

An investigation was conducted at Kaha Vegetable Research Farm in the Kaliobia Governorate from 2021 to 2023 with an aim to evaluate the performance of six inbred lines of summer squash and their fifteen crosses in both open field and plastic greenhouse conditions. The study spanned two successive summer seasons (2022 and 2023) and focused on assessing horticultural traits and resistance levels to the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Significant variations were observed in the mean performance of all traits among different genotypes. Analysis revealed significant differences in both general (GCA) and specific (SCA) combining abilities for all studied traits, except for the number of days to anthesis of the first female flower, indicating the presence of both additive and non-additive gene effects in traits inheritance. In the plastic greenhouse, genotype P3 exhibited the highest resistance with an average of 10.6 mites per 2 inches², while the cross P2 × P6 showed tolerance with an average of 4.4 mites per 2 inches². This study highlights the potential of new summer squash hybrids with desirable horticultural traits and resistance to the two-spotted spider mite. Additionally, parent 222/2 (P1) demonstrated the best combining ability for all traits, while parents 264 (P5) and 240/3 (P4) were the most effective combiners for total yield. Breeders may leverage these parents for genetic enhancement and the production of hybrids with superior horticultural qualities. Overall, this research provides valuable insights for researchers, breeders and farmers involved in the cultivation, breeding and utilization of summer squash in Egypt.