| چکیده انگلیسی مقاله |
Introduction and Objectives: The production of new hybrids with high production potential, adaptability to climatic conditions and resistance or tolerance to stresses and stability in a wide range of environmental conditions have special importance to increase the yield per unit area. In maize breeding programs based on hybrid production, in order to avoid creating and evaluating a large number of crosses, it is necessary to assign maize lines to heterotic groups. Considering that the heterotic groups have not been determined for the selected maize inbred lines in Iran, the purpose of this research is to investigate the genetic diversity and determine the heterotic groups in the selected maize lines in order to make maximum use of heterosis for future breeding programs. Also, another goal of this research is to classifying the selected Iranian maize inbred lines to early, medium and late ripening groups based on the phenological traits.
Materials and Methods: In this research, with the aim of producing hybrid maize and determining the heterotic groups, 50 selected maize inbred lines produced in Seed and Plant Improvement Institute (SPII) were chosen and evaluated based on their kernel yields, morphological and phenological traits in a randomized complete block design with three replications in the research field of the Seed and Plant Improvement Institute. Also, were performed variance analysis, cluster analysis using Ward's method and principal component analysis.
Results: In general, the results showed that there were significant differences between the traits studied in these selected maize inbred lines. The comparison of the average kernel yield of the inbred lines showed that the inbred line KE77008/1 (from medium ripening group) had the highest yield with 4.708 tons per hectare and the inbred line K615/1 (from early ripening group) had the lowest yield with 1.016 tons per hectare. Also, the range of variation was significant for kernel yield per hectare and other traits among these inbred lines. Therefore, high diversity was observed among the studied lines in terms of kernel yield and other traits. Selected maize inbred lines based on the phenological traits were classified into three groups, early ripening (105.5 to 110 days), medium ripening (111 to 116 days) and late ripening (117.5 to 122 days). The yield range was differed of the early group from 1.01 to 2.74 tons per hectare, the medium group from 1.18 to 3.09 tons per hectare (An exception in the medium ripening group was the line KE77008/1 which had a performance of 4.70 tons per hectare) and the late group from 1.21 to 3.28 tons per hectare.
In genetic analysis, the low difference between the percentage phenotypic and genotypic coefficient of variation of the traits shows that the environmental factors had less effects on these traits. The lowest difference was observed between percentage phenotypic and genotypic coefficient of variation of day to physiological ripening (0.24) and ear height (0.94), which indicates the great effect of genetic factors on the control of these traits. The traits of kernel yield (31.77%), ear height (20.07%), percentage of cob wood (19.96%), number of kernel per row (17.35%) and 1000-kernel weight (16.8%) had the highest percentage genotypic coefficient of variation. Therefore, in this research, these traits are valuable in examining the genetic diversity and grouping of maize inbred lines. However, if the percentage of the genetic variation coefficient is higher, more genetic diversity and less environmental influence is observed for that trait.
Based on the results of principal component analysis, the first component explained 25.67% of the total variation. In this component, the highest positive coefficients are attributed to the number of kernel row (0.518), ear diameter (0.771), leaf number (0.718), plant height (0.668), cob diameter (0.607), ear height (0.50) and kernel moisture at harvest (0.563). The second component explained 19.22% of the total data variance. In this component, the largest positive coefficients belonged to traits of 1000-kernel weight (0.723) and plant height (0.531) and negative factor coefficient related to the number of kernel row (-0.755). Based on the results of clustering by Ward's method, the selected maize inbred lines were classified into six separate groups. The percentage of deviation from the total average was positive for the yield trait in the first and fourth groups. These two clusters based on days to physiological ripening trait were medium ripening. Days to physiological ripening trait for the lines was the highest in the second cluster) late ripening) and was medium in first, third, fourth and sixth (medium ripening), the lowest in the fifth cluster (early ripening) compared to the other clusters. Also, the distribution of the lines based on the first and second principle component analysis and cluster analysis were in significant agreement with each other.
Conclusion: In general, significant differences in yield and yield components were observed in this set of selected maize inbred lines. Also, a high level of genetic diversity was identified in kernel yield, morphological and phenological traits. In general, based on the evaluated traits, 50 selected maize inbred lines were classified into six groups. Additional investigations based on the produced single cross hybrids (KSC 704, KSC 647, KSC 604, KSC 700, KSC 703, KSC 705, KSC 706, KSC 500 and KSC 260) showed that have been done correctly the classifying of inbred lines and identification of heterotic groups. In this study, heterotic group 5 was identified, which has not played a role in the production of famous single cross hybrids. Therefore, using the potential of heterotic group 5 and other inbred lines attributed to heterotic groups that have not played a role in the production of single cross hybrids in the production of new hybrids are worthy of attention.
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