Estudo da patogenicidade e controle biológico de fusarium sp. com trichoderma sp.

Abstract

Phytopathogenic fungi belonging to Fusarium genera are known as the agents responsible of many diseases in plants. Among these, tomato plants are attacked by the 3 races of Fusarium oxysporum f. sp. lycopersici (Fol), which causes vascular wilt. To control this disease, many techniques have been employed, mostly the use of resistant cultivars and chemical fungicides. Alternatively, the use of antagonistic microorganisms for biological control and decrease of inoculum of plant pathogens by introducing mass production of Trichoderma sp. has been studied for many years. In this study we evaluated the pathogenicity of 10 isolates of Fol on differential cultivars of tomato, where only four of ten isolates proved pathogenic to susceptible cultivar to this disease and none of which was diagnosed as belonging to race 3. The results obtained in tests of direct confrontation with Trichoderma sp. isolates showed high variability in relation to mycoparasitism, with the best results for agressiveness the isolates T3, T8 and T17. In these cases it was observed evidence of growth of the host colony for at least six of nine isolates tested. Regarding the inhibitory effect of these isolates, the results of greater inhibition of colony growth of plant pathogenic fungus were obtained for the isolated T3 and T2. The strain 34970 of Fol was the least inhibited by isolates of Trichoderma sp., and isolated TO 11 showed the highest average of inhibition. With regards to the production of volatile metabolites, only the isolates Fusarium 23, Fusarium 27 and 34970 of Fol were inhibited after 120 hours of testing. In the biological control of Fusarium wilt of tomato caused by isolate TO 245, seedlings treated with isolates T6 and T17 of Trichoderma sp. showed a lower incidence of disease, with 1.25 and 0.75 respectively compared to 1.87 of the control group in accordance with scale of severity of disease by Vakalounakis et al. (2004). The treatments with the isolates T6 and T17 in substrate inoculated with isolate 1205/2 showed values of 0.5 and 0.375 according to the scale, compared with 0.5 in the control treatment without the presence of Trichoderma sp. The average height, length and dry weight of roots did not differ significantly for any treatment. The dry weight of shoot was significantly higher for plants treated with isolate T6 in substrate infested by the isolated 1205/2. All the pathogenic isolates of Fol were paired with the standard strains of vegetative compatibility groups and showed signs of heterokaryosis with the standard strain 34970 corresponding to VCG 0030, indicating a possible genetic similarity among the isolates used.