A Study on Genetic Diversity, Heritability, Genetic Advance, and Factor Analysis of Trait Yields and Yield Components in Promising Maize Lines

Extended Abstract Background: Khuzestan, as one of the most important corn-producing provinces of Iran, lacks improved cultivars compatible with extremely hot and dry conditions and relies on foreign cultivars, including the old single cross 704 variety. To prepare suitable cultivars for Khuzestan, lines should be produced and evaluated in the region that can be used in the production of hybrid and open-pollinated cultivars. Methods: To identify and improve the important and effective traits on maize grain yield, 289 corn lines, which were bred in Khuzestan, were crossed with the hybrid single cross 704 and evaluated in two cropping seasons (summer 2016 and spring 2017). The experiment was carried out with a simple lattice square design of 17 × 17 and two replications at the Safi-Abad of Dezful Agricultural Research Center in 2016 and 2017. The traits measured from the growing stage to harvest were plant height, tassel length, tassel branch number/plant, stem diameter, number of leaves­/­plant, ear diameter, grain depth, ear length, number of rows/ear, grain number/row, 100-grain weight, grain yield, biological yield, and harvest index based on the guidelines of the corn and fodder plant department of the Iranian seed breeding and preparation research institute. The yield based on 14% seed moisture along with other traits was measured and calculated from the two middle lines of each experimental plot. The genetic parameters in this research were calculated using the mathematical expectation of the mean square as the basic design of random complete blocks in the form of genetic relationships. To analyze the correlation between the traits and to identify the common factors affecting the studied traits, decomposition into factors was used with the principal component analysis and varimax rotation. Eventually, the analysis of variance (ANOVA) of data and calculation of correlation coefficients between variables were done using SAS Ver 9.20 software and analysis into factors with StatGraphics Ver 19.0 software. Results: The results of ANOVA showed an acceptable genetic diversity among promising maize lines in terms of all studied traits, except for ear length, number of rows/grain, and number of grain/row. The results of the composite analysis in two cropping seasons revealed that the effect of genotype was significant on all studied traits at the level of 1%, suggesting significant genetic diversity among the studied genotypes for all traits. The significance of the genotype × season interaction effect for all studied traits at the 1% level indicates the different responses of genotypes in summer and spring. The highest and the lowest genetic and phenotypic variances in summer and spring belonged to biological yield and seed depth traits, respectively. The ranges of genetic diversity in the studied traits in summer and spring ranged from 1.96 to 32.72 and from 7.63 to 29.88, respectively. Among the studied traits, the highest genetic and phenotypic diversities were observed in the number of tassel branches/plant trait (32.72 and 33.35, respectively). The highest heritability rates in spring were observed for biological yield (97.69%), grain yield (97.43%), grain depth (97.06%), ear length (96.30%), and plant height (95.74%). On the other hand, the highest amount of heritability along with the highest amount of genetic improvement was observed for the biological yield and grain yield traits, both of which can be considered the most important criteria for selecting parental lines in breeding programs based on this study. The results of the analysis of correlation coefficients for the studied traits in summer indicated that the grain number/row (0.81), biological yield (0.72), ear diameter (0.62), and grain depth (0.52) produced medium to high grain yields among the studied traits. In spring, the biological yield (0.86), 100-grain weight (0.65), grain number/row (0.64), ear length (0.64), and ear diameter (0.63) had medium to high effects on the seed yield. The results of analysis in the factor analysis in summer and spring revealed that five hidden and independent factors justified 71.40 and 72.27% of the total data changes, respectively. Five hidden factors for summer were the share of grain yield from the total dry matter (33.10%), plant height factor (15.80), ear diameter component factor (8.80), tassel height factor (7.50), and grain weight factor (7.20). Conclusion: The two factors, namely the share of grain yield from total dry matter and the plant height factor, account for more than 61% of the total justifiable variation of 14 traits in 289 lines. These two factors enable us to define and recognize differences and similarities between the lines that grow in spring conditions in Khuzestan.