Study of Drought and Plant Growth Promoting Rhizobacteria (PGPR) on Radiation Use Efficiency and Dry Matter Partitioning Into Pod in Different Cultivars of Oilseed Rape (Brassica napus L.)

Oilseed rape (Brassica napus L.) is one of the valuable oilseed crops which has been attracting attention in recent years (Arvin et al., 2011). Several factors such as water shortage, low relative humidity, heat and salinity can make drought stress. Radiation use efficiency and yield components are the effective factors of yield formation in oilseed rape. Drought tolerance in oilseed rape depends on other factors except radiation use efficiency. Studies have indicated that plant growth promoting rhizobacterias (PGPRs) has a direct effect on growth and they can cause resistance to the abiotic stress as well. Hence, considering the drought climate in Iran and the effects of PGPRs on increasing resistance to abiotic stress and relief of drought effects and the importance of the cultivation of oilseed rape in Iran, the present research was done with the goal of study of drought and some plant growth promoting rhizobacteria (PGPR) on radiation use efficiency and dry matter partitioning into pod in different cultivars of oilseed rape.
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 in East-North of Iran (36° N, 59° E, 1003 as).Two research sites (under stress and non-stress fields) were beside each other. This region has a semi-arid climate (annual rainfall 286 mm). The experimental design was factorial based on randomized compeletly 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. 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 . Radiation use efficiency and the allocation coefficient of materials to pods were measured in the present study as well. In addition, analysis of variance (ANOVA) was performed using SAS ver. 9.1 software.
Radiation use efficiency There were significant differences between stress and non-stress conditions in levels of bacteria, cultivar and bacteria × cultivar regarding radiation use efficiency. The outcomes showed that the coefficients of radiation use efficiency in each level (bacteria, cultivar and bacteria × cultivar) under non-stress condition was comparatively higher under stress condition. The interaction effects of bacteria × cultivar showed that P. flourescens× Goldrush under non-stress condition with 0.62±0.08 dm.mg-1 had the most and two strains of bacteria× Landrace with 0.1±0.017 dm.mg-1 had the least radiation use efficiency. Regarding bacteria level, Pseudomonas flourescens under non-stress condition with the average of 0.39±0.071 dm.mg-1 had the highest radiation use efficiency. Hayola330 cultivar with 0.45±0.047 and Hayola401 cultivar with 0.39±0.038 dm.mg-1 obtained the greatest RUE under non-stress condition and BP18 cultivar with 0.11±0.06 dm.mg-1 revealed the lowest RUE under stress condition. Both drought stress and simultaneous application with two strains of bacteria had negative effects on RUE.
Dry matter partitioning into pod In this trial, considerable difference regarding pod partitioning coefficient revealed in the level of cultivar and bacteria × cultivar. The value of the pod partitioning coefficient under this investigation ranged from 0.9393± 0.084 under non-stress condition to 0.1634± 0.0210 under stress condition. Although inoculation treatment of bacteria had the synergy effect, co-inoculation treatment had the antagonistic effect of pod partitioning coefficient. Moreover, the rate of the pod partitioning coefficient lessened under drought condition. Berry & Spink (2006) and Arvin et al. (2014) stated that there were positive correlation between HI and partitioning photoasimilate in to economic organs. The results of the present study showed that dry matter partitioning into the pod with a final yield had a 91% positive correlation under non-stress and 74% under stress condition.
In conclusion, negative effects of drought and positive effects of application of bacteria on RUE and pod dry matter partitioning were obtained in this trail. The results illustrated that separate application of bacteria had synergy effect and conflation of two strains of bacteria had an antagonistic effect on both studied traits.