Bactérias epifíticas como agentes de biocontrole da antracnose do mamoeiro em pós-colheita

Abstract

This work aimed to prospect for epiphytic bacteria from leaves, fruits and seeds of papaya; to evaluate the in vitro antagonism of Colletotrichum spp. by the production of diffusible, volatile compounds, chitinase and inhibition of conidial germination; quantify the biofilm production by the selected ones as antagonists and to verify the reduction of the anthracnose severity in fruit discs and in papaya fruits. Initially, 224 bacteria were isolated, among them 74 exhibited at least one mechanism of action against the pathogen, 13 bacteria only two, four had three and one bacterium exhibited all the evaluated mechanisms. The "Mix" were composed of four bacterial isolates, which were distributed in order to balance the antagonistic mechanisms of the isolates in each combination. The 901 isolate was present in all mixtures because it showed all the evaluated mechanisms, being: 1 (901,777,784,916), 2 (901,734, 905, 906), 3 (901, 794, 916, 924), 4 (901 , 794, 905, 906) and 5 (901, 788, 777, 916) were assembled by testing the antagonism of the antagonists by the test of reciprocal antibiosis by displaying at least two mechanisms of action, further adding biofilm production , and applied at concentrations 108, 107 and 106 CFU mL-1 in the fruit discs. All "Mix" significantly reduced the anthracnose in the fruit discs when compared to the control. However, "Mix" 1, 3, 5, at concentration 108 CFU mL- 1, provided better performances reducing the disease to 75%, 89.78% and 90.8%, respectively. Mixtures 3 and 5 at the optimum concentration of 108 were applied to the whole fruits, and the efficiency of the treatments was compared to the synthetic fungicide Comet (Piraclostrobin 250 g / L). The bacterial mixtures did not differ significantly from the fungicide, which reached disease reduction levels above 97%. The combinations used reduced the anthracnose severity above 98%. CAPÍTULO 2 = A total of 224 bacterial strains isolated from leaves, fruit fragments and papaya seeds were evaluated for their performance as in vitro biocontrol agents against Colletotrichum gloeosporioides. The isolates selected as antagonists were also evaluated for biofilm formation capacity, the latter being an additional selection feature. In two of them they were able to inhibit the pathogen in vitro only by the production of diffusible compounds, 47 by volatile compounds, 17 produced chitinase and eight inhibited conidial germination. Of these, 18 exhibited two or more mechanisms, and only one isolate was positive for all evaluated mechanisms. Eighteen bacteria that exhibited at least two mechanisms of action, except for 803 and 883 were submitted to the test of reciprocal antibiosis, and also evaluated, in vitro biofilm production, in times of 24, 48 and 72 hours. Of these, 11 were selected for the in vivo test, in disks of papaya fruits arranged in five bacterial combinations called "mix", in order to increase the effectiveness of the biocontrol and arranged as follows: "Mix" 1 (901,777,784,916), 2 (901,734, 905, 906), 3 (901, 794, 916, 924), 4 (901, 794, 905, 906) and 5 (901, 788, 777, 916). These were evaluated in 3 different concentrations of 108,107 and 106 CFU / mL-1 in reducing the severity of anthracnose in discs and whole papaya fruits. Mixtures 1, 3 and 5 showed efficiency over 75%, 89% and 90%, respectively, in control of the disease in the concentration 108 CFU / mL -1. Mix 3 and 5 were evaluated for disease reduction in whole fruits of papaya, and compared to the fungicide (Piraclostrobina 250 g / 1 L). The experiment was conducted in a completely randomized design, considering the presence of wounds in the fruit peels. The bacterial mixes did not differ significantly from the fungicide, reached disease reduction levels higher than 98%, while the fungicide exceeded 97% in anthracnose control. These results indicate the potential use of bacteria isolated from the target culture as biocontrol agents of C. gloeosporioides in papaya.