Study of Plant Growth Promoting Rhizobacteria (PGPR) and Drought on Physiological Traits and Ultimate Yield of Cultivars of Oilseed Rape (Brassica spp. L.)

Introduction Oilseed rape (Brassica spp L.) is one of the valuable oilseed crops which has been attracting attention in recent years. Iran is located in a semi-arid region, and water shortage has caused problems, namely providing drinking water as much as water supply for crop production. Not only does Plant Growth Promoting Rhizobacteria (PGPR) make plant growth stimulating hormones like Auxin and Gibberellin but also can ease stress conditions by producing ABA. Consequently, considering the current water shortage crisis in Iran, we took three main criteria into account: the roles of PGPRs in increasing resistance to abiotic stress, relief of drought effects, and the importance of cultivation of oilseed rape. The present research has been compiled to study drought and some Plant Growth Promoting Rhizobacteria (PGPR) on Physiological Traits and Ultimate Yield of Cultivars of Oilseed Rape. Materials and Methods The current study was done on the basis of two simultaneous experiments (under stress and non-stress experiments) during 2010- 2011 growing season at Agriculture and Natural Resources Research Station of Torogh, Mashhad is situated in East-North of Iran (36° N, 59° E, 1003 ASL ) . Two research sites (under stress and no-stress fields) were selected beside each other. This region has a semi-arid climate (annual rainfall 286 mm). The experimental design was factorial based on randomized completely block design with three replications in each experiment. The first treatment was Plant Growth Promoting Rizobactria, including B0: no inoculation (control), B1: co-inoculation (Pseudomonas flourescens 169+P. putida 108), B2: inoculation with P. flourescens 169 and B3: inoculation with P. putida 108. Second treatment was cultivar, including Hayola401 and Hayola330 cultivars belong to Brassica napus, Parkland and Goldrush cultivars belong to B. rapa and BP18 and landrace cultivars belong to B.juncea .Greenness index, plant height, relative water content, canopy temperature depletion , harvest index and final seed yield were measured in the present study as well. In addition, variance analysis (ANOVA) was performed using SAS ver. 9.1 software. Result and Discussion The examination of physiological characteristics including Harvest Index (HI), chlorophyll content, and Relative Water Content (RWC) showed that there is a considerable difference between location, cultivar, and bacteria cultivar. At the second stage of sampling, due to the reduction of cell water content and enhancement of concentration of cell content in stress field, the chlorophyll rate was enhanced in stressed locations. While findings in RWC showed that Pseudomonas putida had the highest percentage (64.23%), and no inoculation had the lowest RWC (60.32%). Therefore, inoculation treatment, specifically the individual inoculation in the study of RWC, could ease the effects of drought stress. Results of the final stem height were significant, only in cultivar level and BP.18 with 1.24m was the highest and Hayol 330 with 0.9m was the shortest cultivars regarding to stem height. Individual and interaction effects of bacteria with other treatments on harvest index were significant. In current study, it seems that application of bacteria treatments has caused better formation of final seed yield .There was a considerable difference between location, cultivars and interaction of location×cultivar regarding to ultimate yield. Final seed yield in non-stress location (1351.85 Kg.ha-1) was significantly higher than in stress location (535.38 Kg.ha-1). In the study of both morphological and physiological traits and final seed yield of the current research, Hayola hybrid showed more superiority than other cultivars. Conclusion It seems the individual application of either P. flourescens 169 or P. putida 108 leads to better formation results than two mixed strains of the aforementioned bacteria. In the current study, Hayola hybrids showed a better function in physiology and ultimate yield; therefore, plantation of these hybrids would be valuable even in water deficits as well as application of PGPR