The effect of mycorrhizal fungi and phosphorus solubilizing bacteria on physiological traits and grain yield of red bean (Phaseolus vulgaris L.) in different irrigation regimes

Beans are one of the most important food sources in many parts of the world due to their high protein content. According to geographical conditions, drought stress in Iran is one of the most important threats to agricultural products. Disruption of photosynthesis, destruction of cell structures, reduction of stomatal conductance and plant growth are among the effects of drought stress. Today, the use of biofertilizers based on soil microorganisms is one of the main goals of sustainable agriculture to improve plant condition. In addition to improving soil structure, biofertilizers improve plant growth and yield under stress conditions by increasing root morphology, increasing nutrient uptake and increasing antioxidant power. Due to the negative effect of drought stress on crop yield, an experiment was conducted to investigate the effect of biofertilizers on physiological characteristics and grain yield of red beans in different irrigation regimes.

  This experiment was performed as a split plot base on randomized complete block design with three replications in the research farm of Yasouj University in 2016. Experimental treatments include irrigation at three levels (normal irrigation, irrigation cut-off at the beginning of flowering to the beginning of podding and irrigation cut-off at the beginning of podding to maturity) and biofertilizer at four levels (control (no application) Biofertilizer (application of mycorrhiza fungus, phosphorus solubilizing bacteria and combined application of mycorrhizal fungus and phosphorus solubilizing bacteria). The red bean seed (phaseolus vulgaris) used in this experiment was a Derakhshan cultivar and the mycorrhizal fungus used was Funneliformis mosseae. Phosphorus solubilizing bacteria (Phosphate barvar2) base on Pseudomonas putida Strain P13 and Pantoea agglomerans Strain P5 were used as seed inoculation at planting time. Sampling was done randomly at the beginning of podding stage and in the middle of grain filling with respect to the marginal effect in each block in order to measure percentage of electrolyte leakage, leaf relative water content (RWC), content of photosynthetic pigments, soluble sugars, proline and malondialdehyde (MDA).

  The results showed that different levels of irrigation were significant for traits such as RWC, electrolyte leakage percentage, MDA content, leaf proline content, leaf protein, soluble sugar concentration, total chlorophyll content and carotenoids. The effect of biofertilizer was significant on all traits except the RWC. It should be noted that the interaction of irrigation and biofertilizer was not significant on any of the studied physiological traits except for MDA. Irrigation levels and application of biofertilizers also had a significant effect on grain yield, the combination of both biofertilizers was very effective on grain yield, especially in stress conditions. The grain yield was more than control in the case of irrigation cut-off in the flowering stage and in the case of irrigation cut-off in the stage of podding to maturity by 45 and 38%, respectively.

The results of this experiment showed that drought stress in the form of irrigation cut-off reduced the concentration of photosynthetic pigments, increased the levels of physiological degradation and thus reduced the grain yield of red beans. In conditions of drought stress application of mycorrhiza biofertilizers and phosphorus solubilizing bacteria, by reducing the damage caused by drought stress, prevented the reduction of bean yield. Also, the application of biofertilizers in normal conditions significantly increased the yield of red beans.