Evaluation of genetic diversity in some of Iranian and foreign rice genetic resources based on morphological traits

Rice is the major staple food in Asia and provides 45%– 70% of total caloric intake in many rice-consuming countries (Dato Seri, 2003). The genetic diversity in the rice germplasm is quite large in comparison to other crop species (Roy et al., 2014). Gaining a full understanding of the nature and the extent of diversity in the germplasm is of high importance for different plant breeding programs since despite the increased level of diversity, the range of the selection has expanded and also parents with different genetic materials produce hybrids with greater heterosis, which consequently raises the probability of obtaining superior segregated progenies (Transgressive segregation). Given the importance of rice for food and its strategic position in the global food security, it is necessary to conduct a comprehensive study of the diversity of its germplasm to achieve high yield performance, quality and other important economic and agronomic traits.
In this study, 121 native and exotic rice cultivars including 23 domestic cultivars, 26 improved Iranian lines and 62 improved exotic lines were evaluated to determine the degree of genetic relationship among them based on a simple lattice design (11×11) with two replications. 12 agronomically important traits including days to 50% flowering, number of tiller, plant height, panicle length, leaf length, leaf width, number of filled grain and unfilled grain, grain length and width, 100-grain weight and grain yield were measured. The genotypes were evaluated under field condition at the experimental farm of Rice Research Institute of Iran, Rasht, Iran (37º16΄N, 49º36΄E) in 2014. Numerical values for all the morphological traits were subjected to statistical analysis using SAS program. The effects of genotype on the level of each trait were assessed by two-way ANOVA. Statistically significant differences between means were identified and separated by a Duncan’s test.
The results showed that relative efficiency of lattice design over randomized complete block design (RCBD) for the most of the measured traits was less than 1%, therefore, variance and expected value of mean square were estimated based on the RCBD design. Analysis of variance illustrated a significant difference between the studied genotypes for all the traits at the 0.01 probability level. Phenotypic and genotypic coefficients of variation for most traits were high, indicating great variability in the evaluated traits. The highest and lowest genotypic and phenotypic coefficients of variation were respectively related to unfilled grain and panicle length. The medium value of these coefficients were associated with plant height and tiller number. No significant differences were observed for the genotypic and phenotypic coefficient of variation of the most of the studied traits, indicating that the traits were not greatly affected by the environmental changes. Diverse rice germplasm needs a rational use with a better knowledge of its characteristics. The presented morphological traits in our study demonstrated diversity within and among the studied rice genotypes. This rice germplasm which encompassed a wide range of genetic background and ecologically distinct regions probably contained greater genetic diversity as a result of divergent selection pressure. The factor analysis presented three factors that explained 90% of total variation and according to the factors loading were named related to grain number, plant type and structure and drain dimension, respectively. Cluster analysis results based on Ward's minimum variance and Euclidean distance criteria grouped the cultivars in five main groups that the number of groups was confirmed based on discriminant function analysis and analysis of variance for groups.
The high genetic variability observed in the studied genotypes was based on the assessment of the morphological traits. Morphological characteristics are reliable in the evaluation of genetic variation of rice germplasm. Therefore, the assessed morphological traits of these rice germplasms could provide a performance basis for the selection of potential genotypes for further use in different rice breeding programs (Lestari et al., 2016). Finally, our results indicated that the important agronomic traits in rice can be improved by selecting different cultivars from the genotypes of the first and fifth group and a targeted crossing among them, which will allow to obtain pure and promising lines of rice.