Determining the Heterotic Groups of Selected Grain Maize (Zea mays L.) Inbred Lines using Morphological and Phenological Traits

Background: The production of new hybrids with high production potential, adaptability to climatic conditions, resistance or tolerance to stresses, and stability in a wide range of environmental conditions have special importance to increase the yield per unit areaTo avoid creating and evaluating a large number of crosses in maize breeding programs based on hybrid production, 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, this research aims to investigate genetic diversity and determine the heterotic groups in the selected maize lines to make maximum use of heterosis for future breeding programs.Moreover, this research also seeks to classify the selected Iranian maize inbred lines into early, medium, and late ripening groups based on the phenological traits.Methods: Aiming at producing hybrid maize and determining the heterotic groups in this research, 50 selected maize inbred lines produced in Seed and Plant Improvement Institute (SPII) were chosen and evaluated based on their kernel yields, and morphological and phenological traits in a randomized complete block design with three replications in the research field of the Seed and Plant Improvement Institute.Variance analysis and cluster analysis were performed using Ward's method and principal component analysis.Results: In general, significant differences were observed 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 the medium ripening group) produced the highest yield with 4.708 tons per hectare and the inbred line K615/1 (from the early ripening group) produced the lowest yield with 1.016 tons/ha.Moreover, the range of variation was significant for the 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 the other traits.Selected maize inbred lines based on the phenological traits were classified into three groups, early ripening (105.5-110days), medium ripening (111-116 days), and late ripening (117.5-122days).The yield range of the early group differed from 1.01 to 2.74 tons per hectare, the medium group from 1.18 to 3.09 tons per hectare (except for the medium ripening group containing the line KE77008/1 with 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 of phenotypic and genotypic coefficients of variation of the traits showed less effects of environmental factors on these traits.The lowest difference was observed between the percentage phenotypic and genotypic coefficients of variation in days 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 highest percentage genotypic coefficient of variation was obtained for kernel yield (31.77%), ear height (20.07%), percentage of cob wood (19.96%), the number of kernels per row (17.35%), and 1000-kernel weight (16.8%) traits.In this research, therefore, these traits are valuable in examining the genetic diversity and grouping of maize inbred lines.However, if