Abstract
Introduction
Oilseed rape is the third most important oil crop in the world after oil palm and soybean. The world's oilseed rape production was 4.6 million tons in 2018-2019 and has the ability to compensate for the lack of edible oil in Iran (containing 40-45% oil). The production of this crop is mainly done by using two zero cultivars with a low level of glucosinolate in the feed and the absence of Erucic acid in the oil. Two types of oilseed rape are cultivated in Iran, spring and autumn. Spring type is cultivated in warm regions of the Caspian Sea coast and southern regions of the country and its autumn type is mostly cultivated in cold and mild cold regions.
 
Materials and Methods
In this study 16 rapeseed mutant lines obtained through Gama radiation of three rapeseed cultivars Talaye, Zarfam and Express with 800, 900 and 1200 gray dose rates, followed by 7 selfing generation, are compared during two years for earliness, seed and oil yield and other important agronomic traits in four regions Karaj, Kermanshah, Esfahan and Zarghan with three check varieties. The oil content of rapeseed varieties and lines were determined by NMR (nuclear magnetic resonance) at chemic laboratory of Oilseed Crops Research Department of Seed and Plant Improvement Institute. Finally, the highest yield early maturity lines were defined. Each treatment was sown in plot with four rows, four meters lenght and 30 cm between row distances. The experimental field was prepared in late summer and chemical fertilizer were given to it. The sowing experiment were planned for late week of September until the first week of October.At the end of each cropping year, the yield of each plot was harvested separately and the statistical calculations were carried out after the gathering of two years results by GGE biplot method.
 
Results and Discussion
Results of combined ANOVA showed that main effects of year and genotype, interaction of location ×genotype; year × location, and interaction of year, location and genotype had significant effects on grain yield. The genotypes showed the highest and the lowest grain yield in Kermanshah 4016 kg/ha and Zarghan 2886 kg/ha stations, respectively. Line T-900-4 produced the highest grain yield 3840 kg/ha in all locations. To study the interaction of genotypes and environments, GGE biplot method was used. Based on the polygonal graphs related to genotypes, line Z-800-6, Z-900-7, Okapi and Z-800-3 produced the highest yield in Karaj, Zarghan, Kermanshah and Esfahan, respectively. Regarding the imaginary ideal genotype graph and biplot of genotypes and environments and seed yield ranking, line Z-900-7 were identified as the best genotypes due to its higher yield and stability.
 
Conclusion
In Iran, 70% of rapeseed production is done in warm regions and only 30% in cold regions. Therefore, breeding cold-tolerant cultivars by using mutations will increase rapeseed cultivation in the cold region of Iran.