Abstract
In one of our fields, almost all tomato plants were wilted by a bacterial pathogen, Ralstonia solanacearum, if no plant protection treatments were applied. On the field, grafting a cultivar for harvest onto a cultivar tolerant to the pathogen delayed occurrence of wilt. In another hand, we enhanced the water permeability of the soil by mixing with rice chaff and plowing to a depth of 70 cm before sterilizing the soil with hot water (95°C, 250 L/m2). Thus, the percentage of wilted tomato plants decreased to less than 40%. A biocontrol agent, Pseudomonas fluorescens FPT-9601 and FPH-9601, which were mixed in soil for early seedlings, did not suppress the occurrence of wilt. Hot water treatment without enhancing the water permeability of the soil was not effective for plant protection. The temperature of soil at 50 cm depth reached to 60°C when hot water was poured in the soil after enhancing the water permeability; this temperature was sufficient to kill the pathogen. However the temperature at this depth was 35°C when hot water was poured in untreated soil. The density of the pathogen was maintained around or below 102 colony forming units (cfu)/g of dried soil, which is the limit of detection for the pathogen, in the field after enhancing the water permeability of the soil and pouring hot water, but the density was more than 103 cfu/g in the field without any treatment or with hot water only, before wilt occurrence in each year.
