Effects of Nutrients on Self-Inhibition of Germination of Conidia of Glomerella cingulata

SUMMARY: The percentage germination of suspensions of washed conidia of Glomerella cingulata decreased with increasing concentrations of the conidia in distilled water. With 30 conidia/mm.2 greater than 90% germination was obtained, whereas the conidia from the same batch gave less than 3% germination when there were 3000 conidia/mm.2. This inhibition of germination of crowded conidia was nullified by adequate amounts of peptone; but aeration by shaking had no influence, so that oxygen lack was ruled out as a factor in the inhibition. Various adsorbents, ion exchange resins, vitamins and germination stimulating chemicals were ineffective in inducing germination of crowded conidia. Czapek—Dox mineral solution, Hoagland's mineral solution and Czapek—Dox glucose solution gave respectively 10, 30 and 40% germination of crowded conidia. The germination of conidia was improved by repeated washing with distilled water. Addition of various mineral salts and trace elements (Mg, Fe, Mn, Bo, Zn, Mo, Cu) were relatively ineffective or toxic. Glucose, or mannitol did not induce germination. Peptone and phenylalanine were most effective in promoting the germination of crowded conidia, but only in massive doses. Bimodal response of germination of conidia to added nutrients was noticed. Since the conidia germinated, when present at low concentrations in redistilled water without added nutrients, the conidia could not be considered as nutritionally deficient. The beneficial effect of nutrients in promoting the germination of crowded conidia may be due to inactivation of inhibitory metabolites from the conidia.