Inoculation Experiments of White Root Rot Fungus (Rosellinia necatrix (HART.) BERL.) to the Tea Plant and Some Considerations on the Ecology of the Fungus

1. Inoculation experiments of white root rot fungus were carried out using mainly 2-3 years old tea seedlings in pot, to find out the relation between many kinds of inoculum and the outbreak of disease. From the results of these inoculations, the ecology of the fungus was also discussed. 2. Inoculum was applied by two methods : one is "contact" method and the other "mixing" method. By the former method, inoculum was attached to the collar part of the seedlings and by the latter, inoculum was mixed thoroughly with soil in which the seedlings were planted. The inoculation potency of culture media was in the following order of bran medium = rice straw medium > boiled tea stem medium ?? diseased tea root. The disease was caused very slightly with the fungus cultured on PDA. In the mixing method, bran and rice straw media also caused serious disease and PDA was very feeble as the medium for inoculation. 3. The larger amount of rice straw culture of the fungus was inoculated, the more serious disease was observed in the experiments with 2 and 6 years old tea plant. 4. There was no difference in the inoculation potency of rice straw cultures of the fungus within the culture period of 10-150 days. 5. Pathogenicity was widely differed among the fungal strains. Serious disease was caused by the strain in the order of KANAYA > ICHINOSE = IWAEDO > YOSHISAWA > HORINOUCHI. 6. IWAEDO strain was affected in its pathogenicity by the period of PDA culture. One year's culture showed less severity for inoculation than freshly re-isolated culture, and 2 or 3 years' culture caused only slight disease. But KANAYA strain showed no depression in the pathogenicity after 3 years' PDA culture. 7. Inoculum (rice straw culture and diseased tea root) was burried in soil with distances of 0, 1, 2, 3 and 5 cm. apart from the collar part of seedlings. The rice straw culture caused the disease when applied 2 cm. or nearer from the collar part, but the diseased tea root did not unless applied in contact with the seedlings. 8. The outbreak of disease inoculated with the diseased tea root was apt to be uneven. The state of decay of the tea root attacked by the white root rot fungus did not affect the inoculation potency until the decayed root showed spongy-like looking. 9. From the results of these inoculation experiments, the author concluded that the contact inoculation method with 3-5 pieces. of rice straw culture in a bundle gave successful result on the tea seedlings of 2-3 years old. 10.