Effect of increased UV-B radiation on biological control of the gray mold by Clonostachys rosea and on the expression of strawberry defense-related enzymes

Changes in UV-B radiation can have large effects on the management of the pathogen Botrytis cinerea, especially on strawberry production in Brazil. The aim of this work was to investigate the effect of the increased UV-B radiation on biological control of gray mold by Clonostachys rosea and on the expression of plant defense-related enzymes. The experiments were laid out in randomized complete blocks in a split-plot design. The whole-plot factor was represented by UV-B treatments: 1. ambient solar UV; 2. ambient solar UV reduced by 80% (UV-); 3 ambient solar UV supplemented with UV-B lamps (UV+). The split-plot factors were: 1. plants sprayed with water (control); 2. plants exposed to B. cinerea; 3 plants sprayed weekly with an inoculum suspension of C. rosea and exposed to B. cinerea. The latent infection of B. cinerea was evaluated during five weeks per season, after which leaves were collected to assess the peroxidase, polyphenoloxidase and chitinase activities. No significant effect on B. cinerea incidence for irradiation treatments were observed during both seasons, although C. rosea treatments have been able to control gray mold on fruits. The enzymatic activity was related to the ambient condition, not to the exposure of the plants to these micro-organisms. Only UV+ conditions led to an increase of polyphenoloxidase activity in season 2. The results indicate that the increase of UV-B radiation has no influence on the ability of C. rosae to control the gray mold on strawberry.