Assessing indices of drought resistance in three species of canola (Brassica spp.) under restricted irrigation

Introduction Drought stress as the most extending abiotic stress has critical role on seed yield of canola in the dried and semidried regions of the world. Also, Climate changes affected canola production especially in Iran which had more fluctuant precipitation during spring. All growing and physiological aspects of canola plant is adversely affected by reduction of rainfall and increasing temperature milieu so that yield descend. There are many reports which announced vast genetic diversity among different species of canola in response to drought stress and results show that B. juncea had higher seed yield in drought stress condition than B. napus andB. rapa. Many traits and criteria are recommended for screening desired genotypes on the basis: 1) approved their role on drought resistance and yield, 2) comfortable measurement and suitable emergence in life cycle, 3) high heritability and 4) low time and expense for about 8 to 10 percent improvement at dried conditions. Effectiveness of used traits and criteria were investigated by many researchers and they reported that GMP, MP and STI are better than others due to their higher correlation coefficients with seed yield. Materials and Methods In order to study drought tolerance indices of 9 cultivars from 3 species of Brassica genous (B.napus, B. rapa, B. juncea), an experiment at 2 conditions including: terminal growth drought stress and control in 3 years, 2008-2009, 2009-2010 and 2010-2011, was conducted in the form of RCBD with 3 replicates in agricultural and natural research center of Khorassan-e razavi, Iran. Drought stress in terminal growth drought condition was applied by the initiation of reproductive growth after winter low temperatures on the basis of 110 mm evaporation from Class A pan in stress condition and 60 mm evaporation in control condition. Seed yield was measured on the basis of two middle rows after removing of marginal effect and drought resistance indices for each year calculated. Results and Discussion Combined analysis showed that effect of year on seed yield was significant and the highest seed yield (3025.8 kg/ha) obtained at the 1st year of experiment due to higher precipitation and lower temperature during terminal growth and prolonging of growth duration for 25 -34 days in comparing with 2nd and 3rd years. Also, means comparison of seed yield for 3 years showed that canola seed yield at non-stress condition was 2527.7kg/ha and 2049.28kg/ha at stress conditions averagely. Different cultivars showed significant dissimilar responses of seed yield at drought stress conditions with unequal precipitation in three years of experiments. Hyola401, Hyola 330 from B.napus species produced the highest seed yield either in drought stress or control conditions. Bp.18 and Landrace cultivars from B. juncea species had the lowest seed yield equal to 1469.8 and 1581.9 kg/ha, respectively. Drought resistance indices; MP, GMP, and STI showed maximum correlation with seed yield in both condition (drought stress and control). Conclusion    Successful genotypes in restricted irrigation treatment had mainly higher potential yield than others and so this character is suggested for the first step of genotype screening. These genotypes will be introduced if they had also rational yield in limited water condition. This screening strategy can be authorized using STI, MP and GMP indices but using of stability indices such as YSI and YR mislead us for proper selection to have prosperous cultivars for years with high spring rainfall which happen unpredictably due to climatic variation at recent years. Totally, Hayola 401 and Hayola 303 are recommended according to their long term average yield in three years of experiment at both conditions and MP, GMP and STI criteria.