عنوان مقاله [English]
Introduction: Cucumber (Cucumis sativus L.) is one of the most widely cultivated vegetables. Plant length is a quantitative trait is controlled by many genes. These traits are difficult to study due to the complex nature of their inheritance. The combining ability estimation is useful in determining the breeding value of cucumber lines by suggesting the appropriate use in a breeding program. In studying combining ability, the most commonly utilized experimental approach is the diallel design. General combining ability is a measure of additive genetic action; and specific combining ability (SCA) is deviation from additivity. General combining ability is a main effect and SCA is an interaction. The aim is to determine the breeding value of the cross. Heterosis has been utilized to exploit dominance variance through production of hybrids. There are reports on positive and negative heterosis in cucumber however, there are differences between reports. This research was conducted to estimate general and specific combining ability and heterosis in cucumber inbred lines and hybrids to produce hybrids with high yield and quality.
Material and Methods: In the spring of 2014, the seven parental lines and their 21 F1 hybrid were planted at the University of Guilan, in loamy sand field. Three replications were arranged in a randomized complete block design. The sandy loam soil was prepared by plowing and disking and formed into raised beds by plowed and harrow prior to plant establishment. Rows were on 1 m centers and plants were about 25 cm apart in the row. Prior to planting 150 kg·ha-1 of nitrogen from urea and 100 kg·ha-1 of phosphorous from triple superphosphate and 80 kg·ha-1 of potassium sulfate was applied. Side dressing with the same amount of nitrogen and phosphorus occurred at 50% flowering stage. Irrigation with 250 m3·ha-1, three times weekly, was begun at plant first flowering. In each replication, 12 individuals of each line or hybrid were spaced 25 cm within a row (plot) on 1 m centers. Data were collected from 12 plants per plot of each accession. Analyses of variance (ANOVA) of data were performed and where appropriate, ANOVA was followed by LSD mean comparison of trait values. For the combining ability analysis (GCA), measurements of plants within each plot were averaged, and means were used as experimental units for analysis by the computer program Diallel.
Results and Discussion: Genotypes has significant effect on all measured characteristics. The highest plant length was related to B6 line and the lowest plant length was related to A0×B6 and B12×B6 hybrids. The highest number of lateral branch was related to B10×A11, B12×A0 and Guilan while the lowest number was related to A0, B12×B6, A15×A11. The highest plant length to first fruit was related to A4×A11 hybrids and the lowest plant length to first fruit was related to B10, B12, B10×A15 and B12×A4. The mean square of general combining ability (GCA) were significant only for plant height up to the first fruit but the mean square of specific combining ability revealed significant differences for all traits that indicated the important effects of dominance genes in inheritance of traits. Plant height up to first fruit has further general combining which reflects the non-additive genes action. The highest parent and standard negative heterosis for plant length was related to B12×B6 hybrid. This hybrid also showed the highest negative heterosis for number of lateral branch. The highest high parent negative heterosis for plant length to first fruit was related to A11×A4 hybrid while the highest standard negative heterosis was related to A0×A4 hybrid and the highest positive heterosis for this trait was obtained from B10×B12 and B12×A4 hybrids.
Conclusion: Although heterosis is affected a plant length is the primary target for increasing yield in high density cultivation, the biological complexity of this trait makes it difficult to draw meaningful conclusions in order to track individual causal elements involved in heterosis. Cucumber breeders might develop determinate or indeterminate cultivars based on high GCA for certain traits. Cucumber breeders might develop cucumber cultivars with optimal vegetative growth based on high general combining ability for their traits. The results revealed B10 and A4 lines are proposed for hybrid production with optimum vegetative growth. The hybrid obtained by crossing of B12 and B6 are proposed for cultivation with high plant density.