Influence Of PH On Ectoenzymes Activity Excreted From Pathogens Of Chinese Chestnut Seed Rot

This paper focuses on the study of cellulase, amylase and pectate lyase (PL) that excreted from pathogens of Chinese chestnut seed rot named Collectotricium gloesporioides Penz. and Dothiorella gregaria Sacc. Functions of above three ectoenzymes in pathogenetic process were confirmed by their activities determination. Then, optimum pH value of the pathogens growth, lowest pH value that pectate lyase excretion, relationship between pH value and moisture content of chestnut kernel, and regulation of pH value against pectate lyase, were all studied in this paper.The activities of cellulase, amylase and pectate lyase excreted from chestnut inoculated by C. gloesporioides or D. gregaria are higher than healthy chestnut. C. gloesporioides or D. gregaria cultivated in liquid medium can release cellulase, amylase and pectate lyase with certain quantity of activities. So, it can be concluded that those pathogens not only promote the excretation of ectoenzymes but also can release some ectoenzymes. Those ectoenzymes excreted by pathogens are thought as the most important enzymes that induce Chinese chestnut rod. Growth of C. gloeosporioides hyphae and D. gregaria hyphae reached the maximum when the pH was at 7.2. That is to say, pH 7.2 was the optimal pH value of those two pathogens. So, growth of the two pathogens should be inhibited at unsuitable pH value in order to keep Chinese chestnut fresh.In growing season of chestnut, seed kernel pH get the highest value, followed by stigma pH, and then involucrum pH. Along with the maturation of chestnut, seed kernel pH increased and involucrum pH fell while stigma pH kept stable. There are abundant phenolic materials, which are very effective inhibitor against pathogens, in involucrum. Those phenolic materials may be relevant with the variation of pH in growth season of chestnut. Therefore, the reason of chestnut seed rot may be relevant to the kernel pH increasing and disengagement of kernel from involucrum. In storage period, sometimes seed kernel pH increased and decreased in other times. It may be relevant to the moisture content of kernel and the reduction of phenolic materials.The level of pectate lyase (PL) secretion increased when the pH increased during the growth of C. gloeosporioides and D. gregaria. The present results suggest that pH value of host regulates the secretion of PL and may affect C. gloeosporioides and D. gregaria pathogenicity. Critical pH of PL-secreting by both pathogens may be at 5.8. PL secretion was never detected when the pH of the inducing medium was lower than 5.8 or when C. gloeosporioides hyphae and D. gregaria hyphae were transferred from PL-secreting conditions at pH over 5.8 to pH lower than 5.8.