Bactérias de filopano de maracujazeiro como agente de controle biológico da mancha-bacteriana

Abstract

The objective of this work was to select residents phylloplane bacteria passion fruit as a possible biocontrol agent of bacterial spot which is the causal agent Xanthomonas axonopodis pv. passiflorae (Xap) and study the mechanisms involved in biological control. The first stage of selection was based on in vivo tests with 224 isolates obtained from healthy leaves of yellow passion fruit collected from commercial orchards, and 102 from the state of Roraima, 72 from Pará and 50 from São Paulo. These were tested in green-house control of phytopathogenic isolates originating from the states of Roraima (Xap-RR), São Paulo (Xap-SP) and Pará (Xap- PA). After this step, we selected phylloplane residents RR-46, RR-29, RR-133, RR- 98 and RR-14, from Roraima and SP-11, SP-18, SP-22, SP-48 and SP-28, from São Paulo due to the low levels of severity 2,3; 2,8; 2,9; 3,5; 3,6; 3,2; 3,25; 3,55; 4,25 and 6,25%, respectively. There was no antagonist detected from the state of Pará. Were selected isolates RR-14, RR-29, RR-46, RR-98, RR-133, SP-11, SP-18, SP-22, SP-28 and SP-48, for the second stage of selection. This isolates were subjected to tests to check the use of single sources of carbon for verification of niche overlap, antibiosis, diffusion of inhibitory substances in culture medium, production of siderophores and influences the activity of peroxidase enzyme in the plant. The results showed that isolates RR-98 and RR-113 were able to compete only against for Xap-RR, by overlapping niche. In antibiosis by diffusion in a culture medium for isolated RR-29, was able to inhibit three isolates of Xap, from RR, SP, and PA. The strain SP-28 only inhibited the last two. The siderophore production was observed only for the isolated RR-29 and SP-28. No antagonist was able to influence the increase of the peroxidase activity of passion fruit plants which indicates they are not resistance inducers. Niche overlap, competition for iron and / or antibiosis are features that explain the ability to control bacterial spot, mediated by isolates RR-98 and RR-133, RR-29 and SP-28.