Study on response of some oilseed rape genotypes to drought stress

In order to determine tolerant oilseed rape genotypes to terminal drought stress, 13 oilseed rape genotypes including Karaj1, Karaj2, Karaj3, Talaye, Zarfam, Okapi, Licord, SLM046, Modena, WPN5, Opera, WPN2 and GKH305 were evaluated in agricultural research station of Islamabade Gharb since 2010 for two growing season. Oilseed genotypes were planted using randomized complete block design with three replications under normal and drought stress conditions so that irrigation was cut from flowering stage. Combined variance analysis showed that the effect of terminal drought stress was significant for recorded characters except oil content, the number of branches and 1000 seed weight. Results showed that mean of seed yield decreased by 20% due to drought stress so that seed yield in normal and terminal drought stress conditions was 4586 kg/ha and 3736 kg/ha, respectively. This reduction was because of drought stress effect on yield components i.e. pods per plant and seed per pods. Genotype GKH305 had the highest seed yield with 5230 and 3941 kg/ha in normal and drought stress conditions, respectively. Bi plot derived from principal components showed that GKH305, WPN5 Zarfam and had high seed potential meanwhile were tolerant to drought stress. In current study, well known genotypes namely Licord, Talaye and SLM046 had low seed yield under both conditions.

Introduction
Environmental stresses are the most important factors reducing the yield of agricultural products worldwide. Drought is one of the most common environmental stresses that have limited agricultural production and decrease the efficiency of using dry and dry areas.
In the field of drought stress, many experiments have been carried out in the world, but in most cases, the severe interaction between the environment and the genotype, selection of drought tolerant varieties is difficult. Improvement of drought tolerant cultivars is also one of the research priorities of the country. The effect of drought stress on plant depents on genotype, length of drought period, climatic conditions and plant growth stage (Roa & Mandham, 1991).
The occurrence time of drought stress is more important than severity of drought stress (Kazi et al., 2002). Rapeseed plants, which are cultivated like wheat in both dry and wet conditions, generally experience drought stress during their life cycle.
In irrigated areas and areas where surface water is used for irrigation, due to the reduction of rainfall and the use of water resources for the lucrative spring crops, the amount of water is severely depleted. As a result, the intervals between irrigation periods will be long and and plants encounter with water stress during filling seeds. According to some studies, the most sensitive time for irrigation is the flowering and early flowering stage (Richard, 1978; Richard & Thrling, 1978; Richard & Thrling, 1979; Richard & Thrling, 1979b; Pouzet, 1995).
the country's largest cultivation of rapeseed belongs to the northern provinces of the country due to the presence of humidity and rainfall in these areas. However, cold and temperate cold regions like Kermanshah have a good potential for growing canola. In these areas, one of the main problems of canola cultivation is the lack of proper rainfall during the flowering stage of rapeseed and later. In these areas, rapeseed farmers who, in addition to canola, cultivate corn or wheat, canceled the canola irrigation in April, and irrigate wheat and corn, and the cut off of irrigation of canola at flowering and seeding time caused Stress and reduction of canola production. Therefore, identifying genotypes tolerant to late season drought stress in rapeseed is of great importance. In this study, in addition to investigating the effects of drought stress on yield and yield components of rapeseed, the most resistant genotypes to late drought stress were identified.