The Acid-base Property Of Trichothecium Roseum And The Effects Of Different PH Values On Its Infection In Apple Fruit

Trichothecium roseum is an important postharvest pathogen,which can cause a variety of postharvest diseases of fruits and vegetables.However,the acid-alkali property of Trichothecium roseum and the mechanism of infection are unknown.In this study,the changes of pH during the growth of T.roseumin vitro were measured.‘Fuji'fruit was inoculated with T.roseum,the change of pH value at lesion was detected during incubation.Meanwhile,the apples were inoculated with spore suspension at pH 3,5,and 7,and the lesion diameter and the activity of fungus extracellular enzyme and host reactive oxygen metabolism of inoculated fruit were determined.The results show as below:1.During incubation of T.roseum in PDB,the pH value of culture mediumincreased significantly,from 5.41 at 0 h to 7.33 at 72 h,which increased by 35.5%.At the same time,the pH in the lesion of T.roseum inoculated fruit also increased significantly,from 3.54 on0day to 4.84 on 12days,whichincreased by 36.7%.2.After the fruit was inoculated with three kinds of pH spore suspension of T.roseum,the fruit inoculated with pH 7 hadthe largest lesion,which was 35%and 68%higher than that of pH 5 and pH 3 on the 9th day of inoculation.Similarly,pH 7 inoculation resulted inthe highest activity ofpectin methylesterase,pectin methyl polygalacturonase,polygalacturonase,poly-galacturonic acidtrans-eliminase,pectin methyltrans--eliminase,and the highest activity of cellulase and?-glucosidase activity in the junction tissue of disease and health of fruit.3.Inoculation with the pH 7 spore suspension resulted in serious damage of cell membrane at the junction tissue of disease and health of fruit,and increased sharply the permeability of cell membrane and malondialdehyde content.Inoculation with pH 7 also led to more accumulation of O₂^-.and H₂O₂at the junction tissueof fruit disease and health.In addition,the fruit inoculated with pH 7 had the highest activity of NADPH oxidase and the lowest activity of superoxide dismutase,catalase and peroxidase.4.After inoculation with spore suspension at different pH values,we found that there were significant differences in ascorbic acid-glutathion cycling activity of the fruit.Among them,the fruit inoculated with pH 7 had the lowest activity of ascorbate peroxidase,gultathione reductase,dehydroascorbate reductase and monodehydroascorbatereductase.In addition,the fruits inoculated with same pH had the lowest content of ascorbic acid,dehydroascorbic acid,oxidized glutathion and reduced glutathion.It is suggested that T.roseum can increase the environmental pH in vitro and in vivo,the pathogenbelongs to alkalized fungus.The results of applesinoculated with three kinds of pH spore suspension indicated that pH 7 inoculation significantly increase the extracellular enzyme activity of pathogenat the junction tissue of fruit disease and health,promote the destruction of cell membrane and the accumulation of reactive oxygen species,reduce the antioxidant capacity of fruit,and enhance the pathogenicity of pathogen.