In order to develop control technology of Bakanae disease caused by Fusarium fujikuroi using water soluble sulfur complex, we evaluated its control efficacy in vitro, in nursery and field and established optimal condition for rice seed disinfection. In addition, we elucidated inhibitory mechanisms of water soluble sulfur complex against F. fujikuroi by investigating spore germination, mycelial growth and microscopy of hyphae of F. fujikuroi treated with water soluble sulfur complex. The results obtained are as follows:

1. Optimal condition of rice seed disinfection was established by soaking rice seeds for 48 hours in the suspension of 0.5% and 1% water soluble sulfur complex in vitro, and by soaking them for 48 hour in hot water and 1% water soluble sulfur solution, 1% water soluble sulfur complex at 30℃ and 1% water soluble sulfur complex at 20℃ in the green house.

2. When rice seeds were treated under the above-selected seed disinfection condition in rice seed box and paddy field, hot water and 1% water soluble sulfur complex, and 1% water soluble sulfur at 30℃ showed high control value of 100%, but 1% water soluble sulfur at 20℃ showed comparatively low control value of 78.2%.

3. As concentration of water soluble sulfur complex increased, rice root growth tended to decrease. However 1% water soluble sulfur complex did not show negative effect for plant growth such as root length, plant height and No. of tillers.

4. Both of water soluble sulfur complex and NaOH showed high inhibitory effect in spore germination of Fusarium fujikuroi SH08. One ppm of water soluble sulfur complex and NaOH suppressed remarkably spore germination by 99.0 and 99.8%, respectively. Based on these results, we think these two materials can be significant factors for suppression of Bakanae disease.

5. Mycelial growth of F. fujikuroi SH08 was inhibited by NaOH for 10~15days after cultivating. But water soluble sulfur complex was shown high suppression than NaOH in terms of effect continuance time and degree of growth suppression.
6. We confirmed that cytoplasmic contents were released from hyphal bodies of F. fujikuroi, when water soluble sulfur complex were treated on PDA discs containing F. fujikuroi on slide glass. This suppressive mechanism of water soluble sulfur complex might be a key factor for the suppression of Bakanae disease.

7. In summary, hot water of 60℃ and 1% water soluble sulfur complex treatment showed high control effect in seedling nursery and in the field, and did not show any phytotoxicity related to plant growth. Therefore, we think the combined treatment of hot water and 1% water soluble sulfur complex can be used as an effective control tool for controlling Bakanae disease in the farms.