• The Korean Journal of Pesticide Science
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• v.4 no.4
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• pp.66-71
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• 2000

Effect of temperature on resting spore germination of Plasmodioprora brassicae was indirectly estimated based on examining temporal change of number of inactive resting spores. Resting spore germination was the highest at $28^{\circ}C$ reaching 55.6% and 82.5%, 24hr and 132hr after treatment, respectively. Optimum pH for resting spore germination was pH6, following pH7 and pH8, and the germination was inhibited at pH 4, and pH9. termination of resting spores was stimulated by root extracts of radish, Chinese cabbage and kidney bean, but inhibited by that of lettuce. Number of inactive resting spores was increased as temperature increases and time prolongs after temperature treatment. However, degree of inactivation of resting spores after 1hr at $40{\sim}65^{\circ}C$ was similar with $40{\sim}60%$, but rapidly increased to 91.5% at $70^{\circ}C$. When root galls were submerged in water, density of inactive resting spores was increased rapidly and reached 60.3% 9 days after treatment. Flooding of infested soil resulted in 30% reduction of survived resting spores 5 months later. Among the two registered fungicides, fluazinam was better for inactivation of resting spores than flusulfamide, but both fungicides were inferior to phosphoric acid.

• The Korean Journal of Pesticide Science
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• v.4 no.4
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• pp.61-65
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• 2000

Effects of temperature, soil moisture level, flooding, and soil microflora on decay of root galls in club root disease of Chinese cabbage were examined in the laboratory. Number of days required for complete decay of root galls was 3 days at $32^{\circ}C$ or higher, 12 days at $16{\sim}20^{\circ}C$ and 28 days at $8^{\circ}C$. As soil moisture content goes up, root gall decay became faster resulting 3 days for complete decay under saturated moisture condition at high temperature of $32^{\circ}C$, and 8 days under the same moisture level at $24^{\circ}C$. Soil moisture effect was relatively low at $24^{\circ}C$ compared to $32^{\circ}C$. Stimulation of decay by soil flooding was not observed at $32^{\circ}C$ but became apparent at $12^{\circ}C$. Influence of soil microflora on root gall decay was negligiable. Based on these results, temperature appears to be the most important factor affecting root gall decay in soil. Root gall decay is thought to be affected more easily by other environmental factors under low temperature conditions. Maturity of resting spores of Plasmodioprora brassicae in root galls tended to increase as time prolongs during root gall decay. Density of the resting spores was lower in fresh root galls where their maturity was also low as compared to completely decayed root galls. Number of resting spores in completely decayed root gall was $6.5{\times}10^{6}/g$ tissue and its maturity was over 95%.