EFFECT OF FILTRATION OF SOLAR LIGHT ON THE PRODUCTION OF CONIDIA BY FIELD ISOLATES OF BOTRYTIS-CINEREA AND ON SEVERAL DISEASES OF GREENHOUSE-GROWN VEGETABLES

New custom-made polyethylene films with light blockers in the far-red region of the spectrum were tested for their effect on sporulation of Botrytis cinerea. A pink-pigmented polyethylene sheet partially screen ed visible light mainly from 470-650 nm, with lowest transmissibility at 500-580 nm, and a green-pigmented sheet partially screened it mainl y from of 560-800 nm, with lowest transmissibility at 600-700 nm. Both films screened ultraviolet radiation up to 380 nm. Light filtration i nhibited sporulation of B. cinerea cultures on artificial medium, toma to leaves, and cucumber fruits. However, the extent of inhibition vari ed with fungal isolate, the quality of the light that reached the cult ure and the medium that supported the fungal colonies. Some isolates s porulated in darkness, so an indirect effect on the host plant has bee n important in reducing the disease suppression. The green-pigmented p olyethylene reduced conidial load and grey mould in commercial greenho uses by 35-75%. Diseases caused by Sclerotinia sclerotiorum on cucumbe r, Fulvia fulva on tomato and cucumber powdery mildew also were reduce d. The green film could be incorporated in disease management. (C) 199 7 Published by Elsevier Science Ltd.