Background And Objectives
Fusarium wilt of melon (Cucumis melo L.), caused by Fusarium oxysporum Schlechtend: Fr. f. sp. melonis W.C. Snyder & H. N. Hans., (Fom), inflicts important yield losses in melon crops worldwide. Fusarium wilt is difficult to control even if long crop rotations are used because Fom colonizes the roots of a broad taxonomic range of plants. Genetic diversity of plants determines their potential for improved efficiency and hence their use for breeding, which eventually may result in enhanced disease resistance. One of the important approaches to resistance to Fom race 1.2 is hybridization and subsequent selection. Parents choice is the first step in plant breeding program through hybridization. In order to benefit transgressive segregation, genetic distance between parents is necessary. The higher genetic distance between parents, the higher heterosis in progeny can be observed. The main objective of this study was to capture the potential genetic diversity between melon genotypes by using cluster analysis. The results of present study have been used in selection of appropriate parents for breeding program
Materials And Methods
In this study, 57 Iranian endemic melon genotypes were screened against race 1.2 of Fom. Artificial inoculations were performed with a suspension of 1 × 106 conidia/ml at one to two true leaf stage. Disease reactions of the genotypes were scored using a 1 to 5 scale. Five traits including phenol compounds (PCs), area under disease progress curve (AUDPC), disease severity, Percentage of dead plants and latent period were assessed.
Analysis of variance showed significant differences between genotypes for all the traits. The highest and lowest AUDPC were observed in Shadegani-2 and Isablle, respectively. According to PCs results, the highest and lowest PCs were observed in Isablle and Khatoni sang bas, respectively. Also, based on cluster analysis, the genotypes were classified into five groups.
On the basis of the greenhouse experiments, significant genetic diversity among melongenotypes, and resistant and susceptible ones were recognized. The results revealed that resistant genotype(s) of melon demonstrate increased accumulation of PCs in response to Fom 1.2 isolate Maharloo. The highest genetic distance was observed between genotypes of second and fifth groups. Accordingly, the crossing between genotypes with maximum distance can form the basic population for the study of action and identify the gene(s) involved in tolerance to Fusarium wilt.