Evaluation of quantitative characteristics of ten spring rapeseed genotypes in Ramhormoz region of Khuzestan

Rapeseed cultivation as an important oil seed crop for edible oil supply in Iran and therefore, the identification of cultivars adapted to the particular environmental condition of each region have a particular importance in terms of attaining higher yield in the current state of the country (Hasan et al., 2014). On the other hand, recognizing the relationships between agronomic traits and determining the contribution of each of these traits to yield production provides the necessary information for the breeders to select the most suitable genotype for each region (Basalma, 2008; Marjanovic-Jeromela et al., 2008). Therefore, the purpose of this study was to determine the contribution of effective traits to grain yield and identify the most effective traits as criteria for selecting high yielding cultivars in Ramhormoz region.

This research was carried out in a randomized complete block design with three replications and ten spring rapeseed genotypes in the cropping year of 2016-2017 in Ramhormoz. The quantitative traits in this study included the number of flowers on the main raceme, siliques on the main raceme, ratio of siliques produced per flowers produced, number of lateral branches, siliques on the lateral branches, grain per silique, 1000-grain weight, silique length, plant height and height of the lowest silique from the soil surface, grain yield, biological yield, number of days to flowering and days to end of flowering, number of days to silique formation and days to maturity, duration of flowering and duration of silique formation to maturity.

The studied rapeseed genotypes showed a significant difference in the all investigated traits except for success ratio for flower development into silique (%). The Safi6 with the highest number of siliques per plant, Hyola420 with the relatively high number of grain per silique and the highest grain weight and SAN34 with the highest number of grain per silique produced the highest grain yield. These three genotypes also had longer flowering duration. Despite the high number of siliques per plant, the late maturity genotype of Hyola60 with the lowest number of grain per silique and the relatively low grain weight had the least grain yield, due to its grain-filling coinciding with the end of the growing season and heat stress. Among the studied traits, the number of grains per silique had the most positive and significant correlation with grain yield and in stepwise regression analysis, it was the first trait which was entered to the model and explained 71% of the variation of yield along with the number of siliques on the lateral branches, 1000-grain weight and the height of the lowest siliques from the soil surface. According to the results of path analysis, the number of grain per silique had the most positive direct effect on grain yield. The indirect effects of this trait via the number of siliques on the lateral branches, 1000-grain weight and height of the lowest silique from the soil surface were negligible. In spite of the relatively high direct effect of the number of siliques in the lateral branches on grain yield, there was no significant correlation between the number of siliques on the lateral branches and grain yield, due to the negative indirect effect via 1000-grain weight and height of the lowest silique from the soil surface

The results of this study showed that Safi6, Hyola420 and SAN34 were the most suitable genotypes to achieve the highest yield in Ramhormoz region (with consideration of the recommended planting date). Grain number per siliques with the highest positive direct effect on grain yield and negligible indirect effects via other traits was introduced as criteria for selection of high yielding genotypes in spring rapeseed breeding programs.