Evaluation of reaction of some rice (Oryza sativa L.) genotypes to salinity stress at seedling stage

Introduction Rice (Oryza sativa L.) is the main staple food for more than half the world's population, and its world consumption has reached about 505.80 million tons in 2017 (IRRI, 2018). Rice cultivation has a special importance in Iran and its harvest area is estimated about 859100 hectares (Agricultural Statistics, 2017). Salinity is one of the environmental stressors that threaten not only the growth of plants, but also the extent of the distribution and diversity of plants in different ecosystems (Ismail and Horie, 2017). Currently, half of the arable lands of Iran (9.59 million hectares) are affected by salinity, which has a major impact on culturing area, and amount of the crop production, (Nabiollahi et al., 2017). Thus, the aim of this study was to evaluate the genetic variation, Heritability and Genetic Advance of among rice genotypes in terms of physiological characteristics and selection of the best parents for use in rice hybridization programs. Material and Method In order to study of diversity among 11 rice genotypes under salt stress condition plotted in an experiment as a split-plot based on randomized complete block design with three replications in summer 2012, at the farm of college of Agriculture, Yasouj University. The main plots were considered for 4 levels of salinity (0, 44, 88 and 132 m‌M), and the subplots for 11 rice genotypes including Gharib, Local Yasouj, Champa and Shahri Loudab, 304, Lenjan- Askari, Kamfirooze, Domsiah mamasani, Mossa-Tarom, Hassan-Serayi. The physiological parameters (F0, Fm, Fv, Fv‌/‌Fm, chlorophyll, soluble carbohydrates, protein and proline leaves) were evaluated one month after salinity stress application. Characteristics of chlorophyll fluorescence (F0, Fm, Fv, Fv‌/‌Fm) and chlorophyll leaves were recorded using a Flow cytometry Model (OS1-FL). Irigoyen et al (Irigoyen et al., 1992) method used for measurement of leaf soluble carbohydrates, Paquine and Lechasseur, (Paquine and Lechasseur, 1979) method for leaf proline, and Liu and Zhang (2000) method for leaf protein. At maturity stage, 2 plants of each pot were selected, and then plant grain yield was measured as the number of grains per spike. Results and Discussion Study of the genetic and phenotypic variation coefficients in salinity stress conditions showed that the maximum and minimum of these coefficients were belonged to grain yield and fluorescence characteristics, respectively. Grain yield under stress conditions showed a positive and significant correlation with Fv, chlorophyll and Fv / Fm, indicating that with increasing leaf chlorophyll content and Fv / Fm leaves, more photosynthesis is carried out,and thus the grain yield increases., leaf protein content had the highest, and F0 the lowest broad sense heritability, under stress conditions. Based on the results of cluster analysis, using the minimum variance method based on the 12 Euclidean distance, the genotypes under both stress and stress conditions were classified into 4 separate groups. In salinity stress conditions, a cross between the genotypes of the first and the fourth groups, which have the highest genetic distance in terms of the studied physiological traits, can be used for hybridization programs, transgressive segregation, and other breeding programs for finding tolerant genotypes to salinity. Conclusion In general, due to the results of cluster analysis in salinity stress conditions, in order to create dwarf, early and high yielding genotypes, the genotypes in the first and the fourth clusters can be considered as suitable and parents in the necessary and targeted crosses between them for improvement the important Physiological characteristics, and to access to the superior salinity tolerant and high product genotypes.