Association between Bacillus subtilis BV02 and a copper-based product in controlling Asian soybean rust

ABSTRACT

The fungus that causes Asian soybean rust, Phakopsora pachyrhizi, shows crossed and multiple resistance to the three chemical groups of site-specific fungicides (triazoles, strobilurins and carboxamides). This fact evidences the need to implement strategies for the preventive management of resistance. An alternative can be the use of microorganisms capable of interfering in the development of pathogens, as well as of acting as resistance inducers in the plants. The objective of the present study was to evaluate the efficacy of a biological product based on Bacillus subtilis BV02, alone or in association with a copper-based product, on Asian soybean rust control, as well as the agronomic performance of soybean. Thus, two experiments were developed, one in the field and another one in the laboratory. For the experiment conducted in the field, a randomized block design was used with (5x2)+1 factorial arrangement of treatments, including four replicates. The first factor corresponded to application, during post-emergence of soybeans, of five B. subtilis BV02 doses (0, 0.5, 1.0, 2.0 or 4.0 L c.p. ha^-1). The second factor corresponded to association or not with a copper-based product. The additional treatment consisted of applying the fungicide association [azoxystrobin + benzovindiflupyr] + mancozeb. In the laboratory experiment, germination of Phakopsora pachyrhizi uredospores in Elisa plates was evaluated in a completely randomized design with eight replicates. Treatments were the same as those adopted in the field experiment, except for the chemical fungicide, since mancozeb was not added to the sprayed broth. Increasing doses of B. subtilis BV02, applied alone, provided reductions in Asian soybean rust severity, and this behavior was not observed when it was applied in association with the copper-based product. Considering the association between B. subtilis BV02 and the copper-based product, the best Asian rust control results were found with doses equal or inferior to 1.0 L c.p. ha^-1. Soybean yield was superior to that of the treatment containing fungicides with the use of B. subtilis BV02 alone (1.0 and 2.0 L c.p. ha^-1), with application of only a copper-based product and with the combination of this micronutrient with B. subtilis BV02 (2.0 L c.p. ha^-1).

Keywords
biological control; leaf diseases; Glycine max ; Phakopsora pachyrhizi