Survival of plant growth promoting rhizobacteria [PGPR] in soil under pesticide stress

ABSTRACT

A study was conducted to determine the effects of pesticide application at different doses on the population density of two important plant growth promoting rhizobacteria [PGPR] Methylobacterium spp. And Bacillus spp. These bacteria play an important role in plant growth promotion and as such are associated with the soil's nutritional value. The purpose of the study was to find whether or not pesticides do affect these PGPR and ultimately lead to environmental stress. Four organophosphates and four biopesticides were used for the purpose of the study. The results revealed that pesticide applications caused a drastic reduction in the microbial population present in the soil, especially Methylobacterium sp. which was completely extinct in soil treated with Chlorpyrifos, Phorate and Dimethoate, except for [count of 0.7 x 106, 30 days, R.D. in Phorate treated soil], [106, 40 days and 0.55 x 106, 30 days, 2 R.D. in Chlorpyrifos treated soil]. The same species proliferated well in biopesticide-treated soil except for a reduction in Neem treated plates [2.4 x 106 in R.D as compared to 3.3 x 106 in control]. Increased doses of Dimethoate and Chlorpyrifos had profound effects on the Bacillus sp. population. In the case of biopesticides, only Karanj had a negative impact on its count, especially at 10 R.D., maybe as a result of its antibacterial effect. So, our present research focuses on the extensive use of biopesticides from a sustainable agriculture point of view.