稲小粒菌核病菌

Studies on the relation between carbon or nitrogen sources in the culture media and the growth of rice stem rot fungi, Leptosphaeria salvinii and Helminthosporium sigmoideum var. irregulare were made. The results were as follows : 1. Vigorous mycelial growth (measured as the dry weight of mycelial mats including sclerotia) of the fungi was obtained when cultured with the liquid medium, containing as the carbon source maltose, sucrose, fructose, glucose, xylose, dextrine and soluble starch respectively. Both sclerotial formation and reddish pigment production in the media by L. salvinii were increased in parallel with mycelial growth. Increases of pH values of the media during the growth of the fungi were higher with L. salvinii than H. irregulare. 2. In comparison of three concentrations (0.5, 2 and 5%) of sugar (glucose and sucrose respectively) used as the carbon source, the more the sugar concentration the better mycelial growth was obtained, and reached its maximum at 21 days from inoculation when cultured with 30 cc. medium at 28℃, while the economic coefficient of sugar (mycelial weight/sugar consumed x 100) was higher in the lower concentration of sugar. 3. In the culture experiments of these fungi with the medium containing, as the carbon source, TCA cycle member organic acid, pyruvic acid, citric acid, a-ketoglutaric acid, malic acid, fumalic acid, succinic acid and acetic acid respectively, it was observed that pyruvic acid was the best for the mycelial growth, and sclerotial formation was resulted. Fairly good growth of mycelia was also obtained on the medium containing a-ketoglutaric acid, fumalic acid, succinic acid and acetic acid respectively. 4. Vigorus growth of L. salvinii was obtained when cultured on the medium contained asparagine, glutamic acid, alanine and aspartic acid as the N-source respectively. No good growth was obtained when each of cystine, lysine, leucine and threonine was added, though they were the memberes of the amino acids found in rice stem. 5. As to the relation between the sucrose peptone ratio (C/N ratio) of the medium and the growth of L. salvinii, higer rate of both growth and pigment production was obtained in the case of the medium of higher C and N concentration than that of the lower. PH values of the media were increased with the decrease of carbon, while it was vice versa in the case of nitrogen . Sclerotial initials were found at about five to seven days after inoculation on the media of all combinations of C and N concentration used.