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Influence of Polychromatic Light, Carbohydrate Source, and pH on Conidiation of Botryotinia squamosa. R. R. Bergquist, Former Research Assistant, Department of Plant Pathology, Cornell University, Ithaca, New York 14850, Present address of senior author: Hawaii Agricultural Experiment Station, University of Hawaii, Kapaa 96746; R. K. Horst(2), and J. W. Lorbeer(3). (2)(3)Assistant Professor, and Associate Professor, respectively, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 62:889-895. Accepted for publication 16 February 1972. DOI: 10.1094/Phyto-62-889.

Botryotinia squamosa (Botrytis squamosa) does not produce conidia readily in vitro when grown in pure culture under fluorescent or incandescent irradiation, fluorescent plus incandescent irradiation, or diffuse sunlight. It sporulates on necrotic onion leaf apices in the field during midsummer in New York State. Abundant conidiation in vitro occurred in 5 to 7 days when the fungus, grown on potato extract-mineral salts medium at 18 C, was exposed simultaneously to BLB near-ultraviolet (near-UV) and cool-white fluorescent lamps for a 14-hr photoperiod. When supplemented during the first 4 hr with cyclic incandescent lighting (1 sec light, 1 sec dark), the quantity of conidia produced was increased significantly. For conidiation, juvenile mycelium (1 week old or less) was sensitive to near-UV and daylight fluorescent lamps; older mycelium was practically insensitive. Irradiation of sclerotia followed by cold-dormancy stimulated sporulation from sclerotia at 6 to 9 C in 90 days, whereas irradiation of juvenile mycelium at 18 to 23 C stimulated the juvenile mycelium to sporulation in 7 days. Neither the morphology nor the pathogenicity of the conidia was altered. Maximum sporulation was at pH 5.0. Aged soluble starch, dextrin, or potato extract in the medium aided maximum conidiation, whereas mono- or disaccharides were less effective. Repression of sexual reproduction by exposure to near-UV occurred. In paired cultures of compatible matings of B. squamosa, the apothecial initials aborted and conidiation commenced on the stipe tissue. The initiation and inhibition of both sexual and asexual reproductive processes were dependent on length of exposure and quality of irradiation.

Additional keywords: spore formation.