Changes In The Apple-pear (pyrus Bretchneideri Rehd.) Black Spot Latent Infection And Its Pre-synthetic Antibacterial Substances And Induced

Alternaria rot caused by Aliernaria alternaia is a main disease which occurs during Pingguoli pear storage in Gansu province. The occurrence and infection pathway of the pwhogen were examined with the methods of pathology, etiology and histology, and the preformed antifungal compounds were extracted, isolated and identificated from the peel of the fruit with the method of pathologic physiology. It wa~ also surveyed the effect of postharvest treatment with CaCI2, chitosan, salicylic acid and hot water on incidence of Alternaria rot and relationship betwt:en posthanest treatment and induction producing antifungal compounds of frui:s. Alternaria rot of Pingguoli pear belonged to the typical latent infection. At cold condition(Ot,RH 85-90%), fruit surface showed sound after 60 days storage; however, black-gray hyphae grew from lenticels or calyx tube after 90 days storage, The tissue collapsed and resulted in visible black spot as the hyphae spreaded. The incidence of Alternaria rot reached 28.86% till 100 days, The fungi isolated from the~.e black spot were identified as Alternaria alternata (Fr) Keissl A. allernata vias able to infect initially through two pathways during growing season and remain latent or quiescent states. The fungi colonized firstly on styles at blossoming. The colonized fungi grew into carpel cavities progressive after 50 days of petal fall. The clonization of the pathogen could be 45% in carpel cavity till the harvest time. The fUngi also attacked fruit surface and remained latent in underlying epidermal cells during fruit development. The clonization of the pathogen at calyx, side and stem of fruit is 40%, 24% and 42.8% respectively at harvest time. 66 A. alternata infected the fruit through lenticels. The conidia attached on lenticel surface geiminated and formed hyphae, which collapsed superficial cell of lenticel. The development of the hyphae was limited due to the lignification of epiderm and its below -4 cells of layers soon, which forced the hyphae to a structure as parenchyma cells which might develope a structure of aggregated cells resembling microsclerotia later and remained in dormancy. Ethanol (methyl alcohol) ichloromethane crude extract from the peel at enlarging stage, harvest and after 100 days cold storage was separated by thin? layer cbromatographic(TLC) plates. The isolated antifungal compounds were detected with conidia of A. ulternata and the inhibition zones at three stages showed difference. By using gas-chromatography and mass spectroscopy (GC/MS) the coripounds in the inhibition zones were seperated and identified. Palmitate methyl, oleic acid methyl, linolenic acid methyl and squalene appeared at the three stages, all their concentration were the highest at the fruit enlarging stage and decreased rapidly at fruit maturation and aging. These compounds might be suggested as a main antifungal compounds in the growing fruits. The phthalate alkyl esters were i elative higher concentration at harvest and after 100 days cold storage, There were 6 phthalat e alkyl esters identified from the peel of after 100 days cold storage, and the relative concentration were up to 60%. These esters might be suggested as the antifungal compounds of postharvest pear. Alternaria ro; of Pingguoli pear could be controled with 6% CaCl2~ 1% chitosan 45 20mm and 50 10mm hot water; however,the fruit treated with salicylic acid had no effect on the rot. By TLC bioassay of the crude extracts from t...