The effect of drought stress on yield and yield components in 10 genotypes of rapeseed under Birjand climate conditions

Rapeseed is an annual plant of the Brassicaceae family (Mobasser and Piri, 2008). The Rapeseed is one of the most important crops in the world for oil extraction. It has the highest annual growth rate among the most important vegetable oils in the worlds. Statistical analysis shows that there have been significant developments in Iran, so that the production has increased from 76 to 350 tons during 2003 to 2013 (FAO, 2014). Today Rapeseed is most important source of oil in America and Europe. Among the oil crops, Rapeseed has specific priority for several reasons. Due to the necessary need for the country to produce oil, has increased the area under Rapeseed cultivation (Pessarakli, 1994; Shekari et al, 1998).
Drought stress, especially in the end of season is one of the most important factors limiting plant growth in arid and semiarid areas (Turhan and Baser, 2004). Drought stress has a negative effect on many plant processes, including photosynthesis and evaporation (Ohashi et al., 2006). During the drought stress reduce the number of flowers per plant, number and size of seeds (Malcom and Doug, 2002). Fanaei (Fanaei, 2008) by research on Rapeseed found that yield components for example the number of pods per plant had a significant difference during the two years of testing. As well as a significant reduction were observed in yield due to the reduction of yield components such as number of pods per plant, number of seeds per pod and seed weight under stress conditions. In another study it was found that the yield of Rapeseed was severely affected by drought stress and decreased flowering period and days to maturity, but did not change significantly the number of days to flowering, grain filling period, plant height and number of pods per plant. The number of seeds per pod and seed weight decreased (Nasiri et al., 2003). The aim of this study was to evaluate the effect of drought stress on ten rapeseed genotypes and identification of tolerant genotypes after flowering stage in Birjand region.
This research was conducted in an area of about 600 square meters in the College of Agriculture, University of Birjand in 2010-2011. The study was performed in a randomized complete block design with three replications and 10 treatments in both normal and stress conditions. Irrigation was done after 90 mm evaporation from class A pan until flowering stage. After flowering stage, irrigation was done after 90 and 180 mm evaporation from class A pan in normal and stress conditions, respectively. Each plot was composed of 4 lines with a length of 2 m. The distance between row and on row was 60 and two cm, respectively. The measured traits was including, day to 50% flowering, seed yield, biological yield, seed weight, harvest index, pod length, number of seeds per pod, number of branches, number of pods per main stem, number of pods per auxiliary branch and the total number of pods per plant.
Analysis of variance showed that all genotypes had significant differences for all traits in normal and stress conditions. The effect of stress was significant in the number of days to 50% flowering, seed yield, biological yield, seed weight, pod length and number of seeds per pod. The stress had no effect on harvest index, number of branches, number of pods per main stem, number of pods per auxiliary branch and the total number of pods.
Mean comparison of different genotypes showed that Hyolla308 and Licord had the highest seed yield in normal conditions. Genotypes Modena, Okapi, Hyolla401, Zarfam and RGS003 did not show significant differences with them. Mean comparison of different genotypes showed that Hyolla308 and Modena had the highest seed yield in stress conditions. Genotypes Okapi, Zarfam, Licord SLMO46 and RGS003 did not show a significant difference with them. Correlation analysis showed that seed yield had a significant positive correlation with biological yield and number of pods per main stem at %1 and %5 levels, respectively, in normal conditions. In stress condition, seed yield had a significant positive correlation with biological yield, harvest index, number of pods per auxiliary branch and the total number of pods per plant at %1 level. Number of pods per plant can be regarded one of the most important components of yield, because the pods contain seeds. In the other hand the seeds involved in growth and development at early stage of seed filling through photosynthesis. Clarke and Simpson (Clark and Simpson, 1978) reported that the number of pods per plant increased the number of seeds per pod, but decreased seed weight. The negative poor correlation between the number of seeds per pod and seed weight decreases seed yield. Mendham et al., 1975 found that increasing the number of seeds per pod is considered a key factor in increased seed yield. Increasing the number of seeds per pod is limited and depends on the length of the sheath that this trait is under genetic control.
Factor analysis showed that the first four factors explained %85 of the total variation in normal conditions. The first, second, third and fourth factor explained %36/76, %20/54 %14/76 and %11/72 of the total variation, respectively. These factors named pods production, yield, seed production and phonological- quantitative factors, respectively. Factor analysis showed that the first four factors explained %86/63 of the total variation in stress conditions. The first, second, third and fourth factor explained %43/78, %18/54, %12/93 and %11/37 of the total variation, respectively. These factors named yield, pods production, morpho-phenological and seed weight factors, respectively.