Evaluation of a Fermented Millet Product of Bacillus subtilis ATCC 55033 as Potential in Biocontrol of Bacteriosis (Xanthomonas axonopodis) in Gulupa (Passiflora edulis Sims)

The “oil stain disease” has become a phytosanitary status that involves economic losses for farmers who produce gulupa (Passiflora edulis Sims). For this reason, this research aimed to evaluate the biocontrol activity of Bacillus subtilis ATCC 55033 in a culture medium based on fermented millet as a biocontrol product of the disease. Initially, metabolite production of seven strains of B. subtilis and a reference strain B.s (ATCC 55033) was evaluated; in addition, the in vitro antagonistic ability was evaluated against Xanthomonas axonopodis. Two experiments were performed under in vitro conditions: (1) study of the presence of halos of hemolysis due to metabolite production; (2) analysis of the antagonistic ability by using double layer. It was observed that concerning the average, a number five times bigger of halos of hemolysis and 10 times bigger halos of inhibition in vitro on the growth of X. axonopodis in the strains B.s (ATCC 55033) and B.s TB2 over other strains. Subsequently, the evaluation was performed under greenhouse conditions, based on a randomized block design, in which two treatments were applied over the soil: (1) application of the fermented medium based on millet with B.s ATCC 55033, 24 h before X.a inoculation; (2) application of 5 d post-inoculation. It was observed that the treatment, previous infective process, obtained an average percentage of severity equal to 42.044%. In addition, after the evaluation month, a foliage restoration was presented. In conclusion, it is suggested that these products could act as inducers in the plant systemic resistance to trigger defense responses to infection of X.a.