Effects of Drought Stress on Canola (Brassica napus L.) Genotypes Yield and Yield Components

Canola (Brassica napus L.) genotypes with wide adaptability to environmental conditions could play a major role in Iran’s oilseed crop production. Selection of high performing genotypes is very important for developing canola cultivation. Water stress can reduce crop yield by affecting both source and sink for assimilation. Canola yield depends on genotype and environmental conditions and response of genotypes to environmental factors. Canola genotypes response to stress depends on the developmental stage and the events occurring prior to and during flowering stage. Resistance to water stress is divided to avoidance and tolerance. Some species are tolerable against water stress. In a while, other species respond ending life cycle, falling leaves and other reactions into water stress. Therefore, investigation of canola genotypes response to water stress in phenological growth stages can be valuable in order to determine resistant or tolerant genotypes.
In order to study the effect of drought stress on canola genotypes yield and its components, an experiment was conducted in 2013-2014 as a split plot based on randomized complete block design with three replications at the research farm, Agricultural and Natural Resources Research Center of East-Azarbaijan, Tabriz-Iran. Three levels of drought stress were considered as main plot (No-stress, stress at the flowering and pod setting growth stages) and 18 canola genotypes including HW113, RS12, Karaj1, KR18, L73, L72, HW101, L146, L210, L183, SW101, L5, L201, HW118, KR4, Karaj2, Karaj3 and KS7 as subplots. Flood irrigation was scheduled at 50% field capacity, 30 and 30% field capacity for no-stress, stress at the flowering and pod setting growth stages, respectively; i.e. soil moisture capacity was maintained at 30% by irrigating to 100% field capacity when available moisture reached 30% in drought stress treatments. An ANOVA was conducted using the PROC-GLM procedure in SAS ver. 9.2 and Minitab ver. 17 to test for normality. Means were separated using Fishers Least Significant Difference (LSD) set at a 0.05 significance level.
As expected, canola genotypes showed different responses to availability of water at flowering and pod setting growth stages. Results indicated that drought stress at flowering and pod setting growth stages had severe influence on canola genotypes yield and its components. L72, L146, L183, L210 and Karaj 2 genotypes tend to produce higher yields compared to other genotypes in no-stress conditions. Hence, these genotypes are suitable for planting in irrigated lands or place that enough precipitation downfall especially in their phenological growth stages. In contrast, these genotypes are not suitable for planting in arid or semi-arid regions like Iran, because the yields reduced severely in drought stress conditions. However, KR18, HW101, SW101 and Karaj3 genotypes could not produce as same yield as L72, L146, L183, L210 and Karaj2 genotypes in no-stress condition, they had minimum yield loss in susceptible phenological growth stages especially flowering growth stage compared to other genotypes. L183 genotype could produce yield similar to tolerant genotypes, but its yield loss was high in comparison with no stress condition.
Based on our findings in this study, KR18, HW101, SW101 and Karaj3 can be considered the best among other 18 genotypes in the selection of genotypes tolerant to drought stress occurring in flowering and pod setting stages. However, this study must be repeated in other climates and different drought stress conditions to acknowledge what we achieved in this research. After that, decision can be made about planting these genotypes tolerant in arid and semi-arid regions. In this regard, we can also do more comprehensive works can be done on breeding of these genotypes, because water crisis will be the future challenge in Iran.