Determination of the Effects of Hot Water Treatments on Spore Germination and Mycelial Growth of Fusarium fujikuroi, the Causal Agent of Rice Bakanae Disease

Bakanae disease, caused predominantly by Fusarium fujikuroi, is an important seed-borne disease of rice that leads to serious yield losses and poses increasing management challenges due to fungicide resistance and limited use of certified seed. This study aimed to determine the thermal sensitivity and in vitro thermal death range of F. fujikuroi by evaluating the effects of different hot water temperature–time combinations on conidial germination and mycelial growth. A highly virulent isolate of F. fujikuroi was exposed to temperatures ranging from 50 to 60 °C for 5, 10, 15, and 20 min. Spore germination and mycelial growth were assessed on PDA, and inhibition percentages were statistically analyzed. Spore germination decreased progressively with increasing temperature and exposure time, with complete inhibition observed at ≥58 °C for all exposure durations and at 57 °C for prolonged treatment. Mycelial growth showed greater thermal tolerance, with total inhibition achieved at 59–60 °C for all exposure times and at 58 °C after 20 min. Overall, spore germination was more sensitive to heat than mycelial growth. These results provide essential baseline information for developing hot water seed treatment protocols and support the potential of thermotherapy as an effective, non-chemical approach for managing rice bakanae disease.