Estimating Genetic Diversity of Advanced Inbred Lines of Squash Based on Yield Traits

Background and Objectives: Squash is one of the important agricultural species of the Cucurbitaceae family that is cultivated in different regions of the country. Until the last few years, there were no improved squash varieties in the country. Production of squash in Iran is based on local populations that are combined from several genotypes. In order to produce improved varieties and preserve internal genetic resources advanced squash inbred lines produced. In this study, genetic diversity among advanced inbred lines of squash was evaluated to identify suitable genotypes in terms of various breeding traits and select them for future breeding programs.

Materials and Methods: 83 S6 inbred lines were produced by inducing self-pollination from seven local squash populations. In total, 22 S6 inbred lines out of 83 inbred lines and their parental local populations were included for evaluation in this study. The experiment was conducted in a randomized complete block design with 3 replications at the Agricultural Research Station of Golestan agricultural and natural resources research and education center. The following quantitative traits were considered in this study: fruits/plant, fruit weight, fruit length, fruit width, seed yield/m2, seed yield/fruit yield ratio, seed length, seed width, percentage of empty seeds and 1000-seeds weight. Data analysis contains analysis of variance, principal component analysis and cluster analysis of standardized mean of traits were performed using the Ward method using R 4.4.2 statistical software, and genetic parameters were calculated using the relevant formulas.

Results: The analysis of variance of traits evaluated in local populations and advanced inbred lines showed significant differences at 1% probability level. The highest coefficient of genetic and phenotypic variation was observed in the seed yield trait and all the traits had high heritability. Based on principal component analysis, the first three components accounted for more than 74% of the variation between genotypes. Any increase in the first component enhanced fruit size and seed width. The second component can be considered the component that affects yield. Fruit diameter, seed length, and percentage of empty seeds had the greatest effect on the third component. In cluster analysis, 29 genotypes including 22 S6 lines and 7 parental local populations were divided into 4 significant groups. The genotypes of the first group had the highest values of fruit weight and fruit length, thousand-seed weight, and seed diameter. The genotypes of the second group had the highest seed yield. The genotypes of the third group had larger fruit diameter and seed length. The genotypes of the fourth group were average for most traits.

Conclusion: The diversity of traits among the inbred lines, in addition to the high heritability of traits, can be used in breeding programs to produce hybrid genotypes with desirable characteristics. Cluster analysis grouped inbred lines 34, 51, and 222 into group 2 (exhibiting the highest seed yield); which can be utilized in the development of high-yielding cultivars. Line No. 249 in the first group (characterized by the highest thousand-seed weight and seed diameter) can be used to develop cultivars with broad seeds charactristic and high thousand-seed weight.