Viabilidade prática de Bacillus subtilis para controle biológico de Colletotrichum acutatum, agente causal da queda prematura dos frutos cítricos
Corrêa, Francisco Eduardo
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The objective of the present research was to study the practical viability of Bacillus subtilis (ACB-69) to control Colletotrichum acutatum, the casual agent of postbloom fruit drop (PFD) under field conditions. First, the bacteria was tested in two different concentrations, one at 5% and the other at 10 %, in the experiment conducted on Pera Sweet orange plants grafted on cravo lemon trees (11 years of planting), in a private property located in Botucatu, São Paulo State, Brazil during the 2007/2008 season. The same treatments were repeated in the following season, however, with or without adding a carbon source (molasses at 5%), on Valencia orange plants grafted on Rangpur lime trees (15 years old). Additional studies were also carried out under the same conditions, aiming to determine the most appropriate growth stages of flowers to apply the biocontrol agent, for the best disease control. For all experiments, the biological products were applied with an air assisted sprayer with the additional intent of evaluating its practicality. It was verified that the weekly application of B. subtilis at 5% reduced the quantity of symptomatic flowers by 47%, while the chemical treatment only showed an18% efficiency when compared to the control. On the other hand, weekly applications of B. subtilis (at 10%) or with one week before the application of the other biological treatments caused a greater average number of effective fruits (ANEF). The addition of a carbon source at the moment of application may favor the antagonism of the bacteria; however, the addition is optional, particularly when its ANEF is evaluated. The best moment to apply the ACB-69 isolate to control PFD was in the open flower stage, when the percentage of symptomatic flowers was evaluated, however, when the bacteria is applied during all flowering stages there is a greater quantity of effective fruits per plant. The use of the air assisted sprayer was considered efficient for the antagonistic application, allowing a better distribution of the inoculum on the plant without damaging the bacterial cells, hence, enabling it to be an indication for future microorganism applications to control diseases.