2017 Volume 83 Issue 2 Pages 95-101
The control of bacterial fruit blotch, caused by Acidovorax citrulli (Aac), a seed-borne pathogen of cucurbits, is important to prevent expansion of the pathogen into new areas in Japan. To establish a more effective hot water treatment to disinfest seeds, we examined effects of treatment temperature, treatment duration and temperature changes on the survival of Aac. To kill off Aac in a short time, intermittent heat treatments of repeated heating (50°C) and cooling (20°C) in turn was more effective than continuous heat without cooling. Because dry heat is not easily transmitted through the large seeds, which also harbor numerous bacteria, the effect of intermittent hot water treatment using hot water and cold water in a small regulated water bath was tested on artificially infested seeds of wet squash. The intermittent hot water treatment was more effective than the continuous hot water treatment for 20- and 30-min durations. The test using a bacterial suspension yielded nearly the same results. Further combining the intermittent hot water treatment with 0.01 M acetic acid and a mixture of 0.168% basic copper chloride prevented infection by Aac. Large amounts of squash seeds can thus be treated in a large regulated water bath to disinfest seeds as effectively as treating small amounts of seed in the small water bath. The optimum condition was a 30-min intermittent hot water treatment (53°C) with 0.01 M acetic acid and a mixture of 0.168% basic copper chloride. Although germination vigor and germination rate of the seeds tended to decrease slightly after the intermittent hot water treatment, germination rate was around 60% and was not in a problem for seed stock.
