Formulações à base de Bacillus spp., para controle de Alternaria alternata f.sp citri

Abstract

In the 2018 harvest, Brazil produced 996.872 tons of tangerines and their hybrids, with the state of São Paulo and Minas Gerais responsible for 59% of this production. However, this productive potential requires the use of a high number of fungicide applications to control one of the main phytosanitary problems, an Alternaria Brown Spot (ABS), caused by the fungus Alternaria alternata f.sp citri. However, the results, besides it not being entirely satisfactory, can have a negative impact on health and the environment. The insertion of alternative methods, such as biological control, can be a efficient and socially correct strategy for controlling the disease. Therefore, the present study aimed to develop Bacillus subtilis (ACB-01) and B. amyloliquefaciens (ACB-08) based formulations, which in previous studies showed potential for controlling ABS. For this, it was evaluated: (i) the addition of nitrogen compounds and trace elements on the antagonistic activity from bacteria; (ii) the use of different carrier materials (talc, kaolin and starch) in the formulation; (iii) the shelf life of Bacillus spp.-based formulations, in two storage conditions (22 and 4 ° C); (iv) the effect of formulations on mycelial growth and germination of A. alternata conidia and, finally, (v) the efficiency of Bacillus spp.-based formulations, in the control of the disease. The results obtained showed that: most of the evaluated additives favored the antagonism of the bacterial isolates, affecting the mycelial development of the phytopathogen; the combination of a nitrogenous compound and a trace element showed a lower antagonistic activity of the bacteria, when compared with the additives used individually; all Bacillus spp.-based formulations, regardless of the bacterium carrier material, were efficient in inhibiting the germination and development of the A. alternata colony; most formulations remained viable until six months of storage at 22 oC; B. amyloliquefaciens ACB-08-based formulations did not maintain viability when stored for six months at 4 oC; there was a difference regarding the preference of additive and carrier material for the development of formulations from Bacillus species; the best formulations for Alternaria Brown Spot control included: B. subtilis ACB-01 grown with MnSO4.H2O (1mM) + kaolin and B. amyloliquefaciens ACB-08 grown with CoCl2.12H20 (0.2mM) + talc and they were compatible with strobilurin, when applied in mixture.