Germination of Conidia of Peronospora Tabacina Adam I. Germination in Vitro

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Abstract
Washed conidia of Peronospora tabacina Adam germinated poorly or not at all in water alone, but germinated in the presence of riboflavin. The rate of germination of conidia in liquid suspension was enhanced by the presence of carbon and nitrogen sources, phosphate, and calcium and magnesium ions. The effects of 141 metabolites on germination and germ-tube elongation have been tested. A number of analogues of natural metabolites were inhibitory to germination and germ-tube elongation. Extracts and exudates of tobacco leaves did not affect either the amount or rate of germination. Washing by centrifugation increased the percentage of conidia that germinated subsequently and the presence of a germination inhibitor in unwashed conidia is postulated. The optimum temperature for germination of conidia on agar, or in liquid suspension, was in the range 15-20[degree]C. The pH optimum varied with the constitution of the medium; when germinated on 2% agar a broad optimum was shown at pH''s 5.5-8.0, whereas in liquid suspension the optimum was in the pH range 6.5-8.0. When conidia were tested within 24 hr from the time of initiation of sporulation, germination was high (85%). After 48 and 72 hr germination had dropped to 61 and 48% respectively. Washed spores showed no loss of germination capacity when kept for up to 6.5 hr. but germination was negligible after 18 hr storage. Visible light did not affect germination, but 9000 uW/cm2 of ultra-violet light reduced it to 2.7%.

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