Evaluation of some Varieties and Mutant Lines of Rice in Response to Thermal Conditions in the Double Cropping System

Extended Abstract Introduction and Objective: During the recent years, rice has again received a lot of attention from farmers in the north of the country by improving the self-reliance coefficient of the product and productivity. On the other hand, temperature drop at the time of flowering and grain filling, despite the quality improvement, leads to a sharp decrease in the yield of the rice in double cropping stage. Therefore, identification of suitable cultivars in terms of precociousness and tolerance to cold, which will result in acceptable grain yield, is one of the priorities of rice cultivation. Materials and Methods: In this research, evaluation of cold tolerance for 24 rice genotypes including five EMS mutant lines, two gamma ray mutant varieties from the Tarom-mahalli cultivar, five foreign lines, three improved cultivars and nine landrace cultivars in the research farm of the Sari Agricultural Sciences and Natural Resources University was carried out in the form of a randomized complete block design in three replications under replanting conditions. At the end of the growing season, various traits such as the number of days to full heading stage, the number of days to maturity, the height of the plant, the number of panicles per plant, the length of the panicle, the number of seeds per panicle, the number of unfilled grains per panicle, the number of fertile grains per panicle, length of grain, 1000-grain weight, panicle harvest index, panicle fertility percentage, grain density and paddy yield were measured. Cluster analysis and principal component analysis were used to categorize genotypes. Result: Out of 24 rice genotypes cultivated under cold conditions at the end of the season, only 14 genotypes reached the heading stage. The results of analysis of variance showed that there is a significant difference between the genotypes in all studied traits. The mean comparison results showed that Zarak and Kohsar cultivars and L181, L183, L184 and L185 mutants were among the low-duration genotypes. The highest and lowest number of grains in the panicle was related to D100 and Binam genotypes with 147.47 and 50.67, respectively. The mean comparison results showed that the highest grain yield of L183 genotype was 339 g.m-2, which was 79% higher than the Binam (control cultivar). The dendrogram obtained from the cluster analysis showed that all the studied genotypes were segregated into four separate groups that the second and fourth group had the highes