Evaluation of Streptomyces spp. for the biological control of corky root of tomato and Verticillium wilt of eggplan

The effects of Streptomyces spp. isolates in the biological control of corky root of tomato and Verticillium wilt of eggplant was determined in in vitro, greenhouse and field trials. Twenty-six Streptomyces spp. isolates were obtained from the rhizospheres of different vegetable crops in southern Italy. In in vitro dual culture tests, mycelial radial growth of Pyrenochaeta lycopersici and Verticillium dahliae was reduced up to 18.6% and 30.1%, respectively. Radial growth of seven other fungal pathogens was variably reduced as well. The isolates StB-3, StB-6, StB-11 and StB-12 showed a good antagonistic effect against both P. lycopersici and V. dahliae, while the rest of isolates eventually showed antagonism against only one pathogen. In pot-experiments in the greenhouse three of the four above-mentioned Streptomyces spp. isolates significantly reduced corky root up to 64.9% (StB-11), and all four isolates reduced foliar symptoms of Verticillium wilt (AUDPC) up to 48.3%, but none of them reduced the severity of vascular browning. In naturally infested field trials, StB-11 significantly reduced corky root severity in tomato by 48.2%, StB- 12 by 35% and StB-6 by 32.6%, but none of the isolates were effective in controlling Verticillium wilt of eggplant. The effectiveness of the streptomycete AtB-42, successfully used in previous researches, was here confirmed as it reduced corky root of tomato in the field by 33.6%. In conclusion, our research demonstrates that under field conditions corky root of tomato, but not Verticillium wilt of eggplant, can be effectively controlled by the Streptomyces spp. isolates used in this study.