عنوان مقاله [English]
Cantaloupe is one of the most important vegetable crops in Iran. In recent years, due to some problems, such as low sweetness and fruit yield, plant death diseases, and the indiscriminate introduction of foreign commercial hybrid cultivars, the genetic resources of this product have been severely eroded. Therefore, in this research the crossing of important local cultivars such as Saveh and Niagara with the commercial and selected F1 cultivar Galia was considered to combine the best traits and select the best genotypes of the F2 generation by pedigree selection method and continuity of generations. This experiment was carried out in the Faculty of Agricultural Technology (Aboureyhan Campus) University of Tehran research farm. The selection of the best genotypes was done in three stages (natural screening in the field for disease, virus, and mite resistance, evaluation based on qualitative traits in the laboratory, and final selection of genotypes based on the results obtained from multivariate analysis of quantitative traits). The results showed that in Niagara × Gallia (NGF2) population, general heritability was high for all the evaluated traits except the fruit shape index. In the Saveh × Gallia (SGF2) population flesh thickness, soluble solids and fruit harvest date had the highest heritability. The results showed that the traits included in the stepwise regression model accounted for 90.3 and 80.3 percent of the total changes related to fruit weight in NGF2 and SGF2 populations, respectively. Based on the principal component analysis, in NGF2 and SGF2 populations, two principal components explained 71.88 and 71.31% of the data variance, respectively. Based on the results of the bi-plot analysis, 30 NGF2 and 53 SGF2 genotypes were selected, and cultivated in order to continue generations and reach pure parental lines in the F3 generation.
Cantaloupe is one of the most important vegetable crops of Iran. In recent years, due to some problems such as low sweetness and fruit yield, high sensitivity to virus contamination and consequent plant death, and especially the excessive import of foreign commercial hybrid cultivars, the genetic reserves of this product have been eroded. Therefore, the crossing of two important indigenous varieties, Saveh and Samsoori, with the severely commercial and selected F1 variety "Cory" in the Galia group, was done to combine the best traits and select the best genotypes of the F2 generation.
Materials and methods
In this research, parental cross were performed between Samsoori (round fruit, striped and slightly fruiting ridges, light cream skin color, fully reticulated, low shelf life, green flesh, medium sweetness, with commercial name of Niagara), and Saveh (round fruit, orange skin color, fully reticulated, netting, with high transportability and shelf life, green flesh and low sweetness, low yield) cultivars both as paternal parents, with F1 hybrid, "Cory" (round fruit, fully reticulated, none striped and ridges, yellow skin background color, very high transportability and shelf life, green flesh, high and stable sweetness, with the aggregation of some resistance genes related to types of damping off and viral diseases, as the maternal parent. The research was carried out in the spring of 2016 at the educational-research farm of the faculty of agricultural technology (Aboureyhan campus), University of Tehran, Pakdasht. The seeds of the first generation resulting from the crossing were planted in the greenhouse in the autumn of the same year and self-pollinated. In order to create a large and diverse population to select the best genotypes, in the spring of 2017, seeds from the F2 generation, including 1000 seeds from the crossing of Samsoori with Galia, and 1500 seeds resulting from the Saveh with Galia crossing, along with their parents and also the first generation seeds, were planted in the seed tray. After four weeks, the seedlings were transplanted, with an interval of 80 x 170 cm, in a rented farm land located in Filistan village, Pakdasht. Controlled pollination (isolation of male and female flowers in the evening before mating and inoculation by hand the next morning) was done for all the plants. So that each plant has at least one fruit that self-fertilized to next generation. The selection was done by pedigree method. After all the plants were sterilized, the health of the plants was evaluated against common and important fungal, viral and mite contamination under the natural conditions of the farm by scoring the severity of the infections. Quantitative and qualitative fruit traits were measured based on nominal, ordinal, and interval scales. To select the best genotypes, in addition to natural selection and recording of quantitative traits in the laboratory, multivariate analysis of quantitative traits was also performed.
Results and discussion
The results showed that in (Samsoori) Niagara × Gallia (NGF2) population, the general heritability parameter was high for all evaluated traits except the fruit shape index. In Saveh×Galia (SGF2) population, flesh thickness, soluble solids, and fruit harvest date had the highest heritability values. The results also, showed that the traits included in the stepwise regression model accounted for 90.3 and 80.3 percent of the total variation related to fruit weight in NGF2 and SGF2 populations, respectively. According to the results obtained from principal components analysis, in NGF2 and SGF2 populations, two principal components explained 71.9 and 71.3 percent of the data variance, respectively. Based on the results obtained from bi-plot analysis, the top 30 NGF2 genotypes and the top 53 SGF2 genotypes were selected and cultivated to produce the F3 generation, continue the generations and finally obtaining inbred lines.
The results indicate that, the optimal use of foreign genetic resources should be considered to improve the native cantaloupe and melon cultivars, and create superior genotypes. This facilitates the acquisition of economically important genes by breeders, which have been eroded over time. Another advantage of this process is that these foreign sources are abundantly available. The conspicuous finding of this research was that the two top native cantaloupe cultivars of Iran are known to have some undesirable traits, such as relatively low sweetness, low yield, and low tolerance to some pests and diseases. Therefore, the introduction of desirable alleles of foreign commercial hybrid cultivars, especially those of the "Galia" group and possible "pineapple" into Iranian cantaloupe genotypes will be promising.