Investigating Role of Organic Acid Production in theBiocontrol Potential of PGPR

Abstract

Plant Growth Promoting Rhizobacteria (PGPR), mainly Pseudomonas sp. are well studied organism. Mainly all the studies on plant for biocontrol as well as PGP traits are mainly done on Pseudomonas sp. Rhizobium are best nitrogen fixing organisms as well as P solubilizers, so people are looking for biocontrol by Rhizobium sp. In this study, we are focusing on Rhizobium sp. as well as Bacillus sp. Which are also PGPR. We had isolated 30 organisms from root nodule and rhizospheric soil of Mung (Vigna radiata) & Tuver (Cajanus cajan). Among them 3 isolates were selected for biocontrol study on the basis of biochemical properties and good PGP activity. One of them is Sinorhizobium sp. and two of them are Bacillus sp. These three isolates having good PGP activity. I35 and I36, which are Bacillus sp. have good phosphate solubilizing capacity with compare to I16 (Sinorhizobium). Further studies proposed that PGPR having good capacity of phosphate solubilization may not produce more amount of antifungal compounds, which play role in biocontrol. So our study mainly focusing on this topic. In our study, we are comparing three isolates Rhizobium sp., Bacillus sp. and Pseudomonas sp., which have biocontrol activity as well as produce organic acid (gluconic acid). I16 which is Sinorhizobium have less capacity of phosphate solubilization on TRP media with compare to Bacillus sp. In in vitro study of antifungal activity, I16, I35 and I36 have good capacity to produce antifungal compound with compare Pseudomonas sp. Further studies shows that environmental factor such as carbon source, temperature, pH, etc. can affect the production of antifungal compound (secondary metabolite). We had studied effect of various carbon source on production of antifungal compound production in vitro. For in vitro study of DAPG and PCA, which is mainly studied antifungal compound, we had determined λ max for both compounds by spectroscopy. Then by using this λ max, we had determine antifungal compound production by various isolates. Carbon source mainly glucose affects the production of DAPG and PCA in all the isolates. We had also studied production of antifungal compound in vivo by pot experiment. In in vivo study, we had observed effect of various isolates on shoot length and root length of Mung and Tuver plant. Comparison of plants which are inoculated with various isolates and control are larger than the plant inoculated with fungi. The plant inoculated with various fungi and isolates shows good PGP activity as well as antifungal compound production of various isolates.