Sensitivity to UV-B radiation is one of the main limitations of biological control of plant pathogens in the field. The effect of UV-B radiation on germination and leaf tissue colonization by the biological control agent Clonostachys rosea was evaluated. There were variations among C. rosea strains in sensitivity to UV-B radiation. The most tolerant strain (LQC62) had relative germination of about 60 % after irradiation of 4.2 kJ m(-2). The deleterious effects of UV-B radiation on C. rosea colonization were overcome by higher conidial concentration. In addition, the tolerance of C. rosea conidia was higher when irradiated over leaf disks compared to agar media, and this is very important information to determine the dose and spray strategies for applying C. rosea in the field.

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There is a lack of information comparing UV-B radiation conidial sensitivity of the biocontrol agent Clonostachys rosea (Cr) and its target pathogen, Botrytis cinerea (Bc). We investigated the interactions in vitro and on strawberry leaf discs between previously selected Cr and Bc strains tolerant to UV-B radiation. Strawberry leaf discs inoculated with Bc, Cr, or combinations of both fungi were exposed to UV-B doses (2.9, 5.9, and 8.9 kJ m −2). Incidence and sporulation of both fungi were evaluated, and the Area Under Incidence Progress Curve (AUIPC) and Area Under Sporulation Progress Curve (AUSPC) were calculated. AUIPC and AUSPC of Cr on leaf discs were negatively correlated to increased UV-B. When inoculated alone on leaf discs, Bc was not affected by UV-B, but when inoculated with Cr the incidence and sporulation of Bc were positively correlated to UV-B radiation dose. In the absence of UV-B, Cr reduced incidence and sporulation of Bc. However, the ability of Cr to control Bc was reduced by 20% to 50% with increasing UV-B radiation. Increasing the applied concentration of Cr conidia 10-fold partially overcame the deleterious effects of UV-B on the ability of the biocontrol agent to reduce Bc sporulation in strawberry leaves. The selection of antagonists must fulfil many requirements; besides being active against the specific targeted plant pathogens, they must be costeffective and have ecological characteristics suitable for the desired use conditions. We suggest that UV-B exposure must be taken into account during the development of bio-fungicides based on Cr.