Effects of biological control agents on arbuscular mycorrhiza fungi Rhizophagus clarus in soybean rhizosphere

Abstract

Microbial activity in the rhizosphere is essential for nutrient cycling, which can contribute to soil fertility and plant growth. This work aimed to evaluate the effects of two biological control agents (Trichoderma sp. and Beauveria sp.) on the functional groups of microorganisms in the soybean (Glycine max) rhizosphere and plant growth. The experiment was carried out in a greenhouse, and five replicates with one plant per pot (1000 mL), containing a mixture of soil: sand (4:1), were harvested and microbial communities evaluated at 7, 21, 45 and 60 days after soybean germination. The populations of heterotrophic bactéria (HBP), saprophytic fungi (SFP), fluorescent pseudomonads (PFP) and the functional groups of microorganisms related to carbon cycling [proteolytics (PP), amylolytics (AP) and cellulolytics (CP)], nitrogen cycling [dry weight of nodules (DWM)], and phosphorus cycling [AM fungi colonization (AM)] were estimated. A soil sample (1 g) was taken from the homogenized rhizosphere soil to estimate the culturable microbial community size. Samples were suspended in 9 mL of sterile saline (0.85%) and aliquots (50 ?L) of ten-fold dilutions spread on the respective culture medium. Plates were incubated at 28 °C and CFU were counted. The results showed that biological controls agents such as Trichoderma sp. and Beauveria sp. presented diferente effects on microbial community and Rhizophagus clarus colonization. Trichoderma sp. had positive influence on plant growth and soil microbial community, except for AM fungi. However, Beauveria sp. showed no significant differences in all evaluations, including plant growth.