ارزیابی نتاج و معرفی ژنوتیپهای برتر نسل دوم حاصل از تلاقی طالبی ’سمسوری‘با رقم تجاری ’گالیا‘

Introduction Cantaloupes, are a group of Cucumis melo cultivars, that have round, fragrant fruits with netted skin. Our country, is one of the top five producers of cantaloupe, and melon in the world. Its original origin, is still debated, but one of the important centers of its diversity, is Iran. Although, native cultivars, such as, Saveh cantaloupe, Samsoori, Rish Baba, and various types of Tiles, are often of good quality, and taste, but they are sensitive to a variety of fungal and viral diseases and as a result, their yield is low. On the other hand, every year new cultivars and hybrids, are introduced by seed companies, which are welcomed by farmers, due to, their better agronomic characteristics, and resistance to a wider range of diseases. Continuation of this process, in addition to severe genetic erosion of native cultivars, and populations, and even the complete elimination of some of them, will have consequences such as, dependence of production on foreign companies, annual departure of currency from the country, and non-exploitation of the country's genetic resources. Therefore, it seemed that by creating a diverse population resulting from the crossing of superior native cultivars with cultivars of commercially resistant hybrid to diseases, and then, successive selections, new cultivars, with desirable traits of both parents, could be achieved. Thus, in this study, heritability, minimum and maximum mean values of parents, and F۱ and F۲ generations, aggressive segregation, and relative frequency of qualitative traits, in F۲ generation, and selection of the best genotypes, in two dispersing NGF۲ populations, were investigated. Materials and Methods Parental cross, was performed in the spring of ۲۰۱۷, between Samsoori cantaloupe cultivar (round, striped fruit, cream skin color, completely reticulate, green flesh, very early ripening fruit, poor transportability and durability, free pollinator and high homogeneity) as the selected native paternal parent, and commercial cultivar from Gallia group, that called Cory and as maternal parent (round fruit, completely reticulate, no striped skin, yellow to cream skin color, high transportability and durability, green and very sweet flesh, high resistance to various plant diseases and viral diseases) and produced by Seminis Company. The first-generation seeds, obtained from parental crosses, were planted in the greenhouse in the fall of ۲۰۱۷, and were self-sown. In the spring of ۱۳۹۷, ۱۰۰۰ seeds of F۲ generation, along with parent seeds, and their first generation, were planted in a seedling tray, in the greenhouses of the Faculty of Agricultural Technology (Aborihan) of Tehran University, and transplanted to the ground, in the rental research production farm, located, in Filistan village-Golzar sector-Pakdasht. Controlled pollination, (isolation of male flowers, and manual inoculation) was performed, for all second-generation plants. Selection for subsequent generations, was done by pedigree method, all plants in F۲ generation, were evaluated, and selected. Morphological traits, such as, plant form and phenological traits, such as, day to fruit harvest, were evaluated, and recorded. Plant health, was assessed against common and important fungal, viral and mites, under normal field conditions by scoring the severity of infections in four categories. Fruit quality traits were measured based on nominal, sequential and interval scales and quantitative fruit traits were also measured. Tables of minimum and maximum values, variances, general heritability, transgressive segregation, etc for quantitative traits, also relative frequency percentages and observed genetic ratios for quantitative traits, were calculated. Results and Discussion The results showed that all quantitative traits in the F۲ population had a general heritability above ۹۰%. The mean of all quantitative traits except soluble solids and fruit flesh thickness in F۱ population was lower than the parental average. In F۲ population, for all quantitative traits, positive transgressive segregation was observed, compared to, the superior parent, and negative transgressive segregation was observed, compared to, the less valuable parent. In the F۲ population, nearly ۸۰% of the genotypes, were completely reticulate, and ۲۰% had less or no netting, on the fruit skin. These results were almost consistent with genetic ratios of ۳.۱. Also, ۳۵% of F۲ population genotypes, were striped and more than ۸۰% of them had yellowish skin color and green flesh color. Due to, the fact that, selection based on traits with high heritability, will be more reliable, and successful in early generations, so, it is better, to select the best genotypes, in this population, based on fruit weight, soluble solids, and early maturity, respectively.  ConclusionIn the F۲ population, positive transgressive segregation was evident for all quantitative traits, favoring the superior parent, while negative segregation was observed for the less valuable parent. Traits exhibiting high heritability showcased a pronounced influence of genetic variance over environmental variance. Consequently, selecting cultivars based on these traits in early generations is expected to yield more reliable and successful outcomes. Therefore, it is better, to selection, the best genotypes in the early generations, in the F۲ population, based on fruit weight, (with high genetic efficiency), soluble solids, day to fruit ripening, and with the pedigree management, of the populations, it is finally, possible to achieve lines, that have the desirable traits, of both parental cultivars. The resulting lines, can be used to produce, new hybrids, or provided, to the farmer, as a single cultivar.