Abstract
When Phytophthora capsici infect a cucumber fruit, several kinds of bacteria are induced to grow associating with the fungus and develop in the lesion. After several days, these bacteria occupy the place of the fungus on the fruit, but have no pathogenicity to cucumber. In this paper the contribution of these bacteria to tissue softening and cell degradation were investigated and discussed.
The macerating and pectolytic activities of the extracts of the lesion in which P. capsici and the association bacteria coexist are in same grade as that of the lesion which is invaded by P. capsici alone. Both activities of the culture fluid of these bacteria are extremely low as compared with those of P. capsici culture. Cellulase activities of these bacteria are low too.
On the contribution of these non pathogenic bacteria to lesion development on cucumber fruit, it is considered that these bacteria increased in number depending on exduate from the degraded host tissue after invasion of P. capsici, although they have little amount of enzymes regarding to softening of the tissue as described above. Then pH of the tissue are shifted to the optimum for macerating action of P. capsici depending on the increase of these bacteria and decomposition of the tissue by the fungus.
Strong pectolytic activity of Erwinia carotovora suggests that the host infected together by P. capsici and E. carotovora results in severe damage.
