Breeding for fusarium wilt resistance and some economic characters in cucumber

Abstract: This study was conducted during 2017 and 2018 at Kaha Vegetable Research Farm, Horticulture Research Institute, Qalyubia Governorate to develop promising hybrids of cucumber (Cucumis sativus L.) for yield and fruit quality characters under fusarium wilt (Fusarium oxysporum) infection stress in Egypt using diallel mating design. The pathogenicity and host range experiment revealed that Fusarium oxysporum isolate No.3 was the most virulent one to the susceptible cucumber cultivar “Beta alpha” and cucumber was the only infected host. The prevalence of the non-additive variance suggested heterosis breeding approach is effective way for improvement of these traits. Most of the traits exhibited significant hybrid vigor for some of crosses based on the better-parent. The analysis of variance showed that all the studied traits were highly significant indicating that both of the parents and hybrids had high variability. Significant general and specific combining ability variances were obtained in all studied traits implying that both additive and non-additive gene effects control genetic expression of these traits. The study showed that lines P2, P4 and P5 had significant positive GCA effects for total yield trait under fusarium wilt stress. Thus, these parents could be successfully used in future breeding programs. Among all the crosses, P1×P3, P1×P4, P1×P5, P2×P4 and P2×P5 exhibited significant SCA effects for both early and total yield characters under fusarium wilt stress. So, these hybrids can be used in future breeding program. The genotypes Kaha1×Dokky2 and Kaha1×Kaha2 followed by Kaha2×Dokky3 as well as Kaha1×Dokky3 were the most resistant genotypes decreasing disease severity correlated with increase in total phenol contents and activities of polyphenol oxidase, peroxidase and catalase as compared to susceptible genotypes, i.e., Dokky3, Kaha1×Dokky1 and Dokky1. The scavenging activity was higher in susceptible genotypes compared with resistant genotypes. Furthermore, there was a high correlation between the total phenol content and the scavenging activity. Results also revealed a noticeable significant correlation between disease severity, total yield and early yield traits. Cluster analysis classified the fifteen genotypes into five clusters with different number of genotypes. Further improvement of fruit yield could be possible through the hybridization and selection in transgressive segregation.