Identification of Cold Tolerant Rapeseed (Brassica napus L.) Cultivars Using Stress Tolerance Indices under Humic Acid Application

In order to identify cold tolerant cultivars of rapeseed (Brassica napus L.) using stress tolerance indices under the influence of humic acid application, an experiment was conducted as factorial split plot based on randomized complete block design with three replications in 2017 and 2018 at Seed and Plant Improvement Research Institute, Karaj, Iran. Factorial combination of cold stress as planting date factor in two levels including 20 October and 20 November, and humic acid factor in two levels including non-application (foliar spraying with pure water) and application (foliar spraying with a concentration of 1.5 per mil at 4-6-leaf stage) were assigned to the main plots and the cultivars were allocated to the sup-plots. The results showed that rapeseed cultivars differed significantly. Based on the results of means comparison, the cultivar WRL-95-07 showed higher yield in both stress and non-stress environments as well as the application and non-application of humic acid than the other cultivars. The correlation of drought tolerance indices with grain yield under stress and non-stress conditions was used to determine the most suitable indices. Arithmetic mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HARM) and stress tolerance index (STI) had the highest significant correlation with yield under normal and stress conditions. Principal component analysis differentiated indices introducing tolerant cultivars and indices introducing susceptible cultivars, and on this basis, the 10 rapeseed cultivars were divided into three groups using cluster analysis. Finally, WRL-95-07 cultivar performed well under stress and non-stress conditions with the use of humic acid, followed by WRL-95-12 cultivar which displayed better performance than the other cultivars under stress conditions when treated with humic acid.