Interaction Of Host-Pathogen On 'Ya' Pear Ring Rot Disease

Pear ring rot,caused by Botryosphaeria. berengeriana f. sp. piricola, is an economicallyimportant disease in China. Because pathogenic germs infect the host pear latently at growthstage, and induce rot during the postharvest period, it is difficult to control the disease. Up tonow, it is still not clearly that the mechanisms of fruit decay and defence reaction due to M.Kawatsukaii Hara. It is necessary to know the mechanisms of ring rot disease, which includedhow the pathogen developing in pear fruit and cause the decay, and how the fruit resistant todisease development. We are planning to study fruit-pathogenic fungus interactions frommorphological level, physiological level, and biochemical level. We expect that we could findthe compounds and there producing condition of pathogenic fungus toxins; that the resistantsubstance and its role and content change during growth and storage. This will provide theorybasis for pathogenesis of pear ring rot and feasible way to control the post-harvest disease.1. In order to make sure the latent infection and rotting stage of the ring rot disease causedby Physalospora piricola, the 'Ya' pear fruit were bagged and un-bagged at different days afterblossom, and the smearing and inoculation with P. piricola conidio-spores were also conductedregularly during the growth of fruit. The results showed that the main infection time of P.piricola to the pear fruit was from 50d to 90d after blossom, the infection was also occurredafter 110d of blossom, but it was not infected before 50d of blossom. The pathogen was easilyinfected the fruit through tiny wounds. The rotting fruit was mainly took place at the stage of40～60d after harvest at the step-cooling storage condition. The fruit inoculated with sporesolution at growth stage was more easily decayed than the control.2. As fluorescent substances exist in skin of pears, we successfully made a anatomicalobservation of pear fresh tissues under fluorescent microscope. Fluorescent mother cell atbottom of peel lenticel had function to defense agaist pathogen, in addition, cuticle, sclereid,tannin cells were defensive structure, also. Surface of the smearing and inoculation with P.piricola conidio-spores flesh were observed by scanning electron microscopy (SEM);Conidiospore germination and appressorium formation completed 24h after inoculation, themycelium developed more lushly and mass hyphae surround the pulp cells after 48h after inoculation. The ultrastructure of flesh were observed by transmission electron microscopy(TEM) showed the hyphae were invaded into pulp cell during 24～36h after inoculation. Usingimmunogold labeling with monoclonal antibody againstβ-1,3-glucan and secondary antibody,β-1,3-glucan were localized in cell wall appositions and fungal cell walls.3. The use of HPLC method enable us to successfully study the component and content oforganic acids. Citric acid, malic acid, shikimic acid were main composition of total acid. Thepathogen growth was inhibited with higher concentration of 50mg/100g Citric acid,50mg/100g malic acid, 60mg/100g lactic acid, 10mg/100g succinic acid, 8mg/100g quinic acid,pH level lower than 5.0. Pathogen invading the flesh induce some new kind of organic acids,such as lactic acid and succinic acid.4. The main defense phenolics with high content at the young stage of pear fruit werephenolics, chlorogenic acid,gallic acid and caffeic acid, which decreased at premature stage.Pear fruit disease resistance reduced with the content of these phenolics all declined duringstorage. The defense resistance of fruit at different stage was closely related to the change of itsphenolics. The pathogen growth was inhibited with higher concentration of 1mg/100gchlorgenic acid, 10mg/100g gallic acid, 5mg/100g gallotannic acid 0.05mg/100g coumaricacid in PSA culture medium,and 7mg/100g gallic acid, 40mg/100g chlorgenic acid,0.5mg/100g gallotannic acid, 1mg/100g catehin 1mg/100g coumaric acid.5. The activities of POD,SOD and CAT in 'Ya' pear fruit inoculated with Botryosphaeriaberengriana and sound pear fruit in growth and storage were studied. The results showed thatmetabolic defense induced by the pathogen including the activities of POD, SOD and CAT, andthe activities of these enzymes markedly increased, which suggested that those enzymes wereclosely-related to pear fruit against B. berengriana infection. The main defense enzymes withhigh activity at the young stage of pear fruit were POD and CAT, the activities of these enzymeat rapid growing stage and pre-mature stage of fruit decreased sharply, except PAL with peakactivity at premature stage of fruit. The main defense enzymes with high activity at thepre-mamre stage of pear fruit were SOD, The activity of SOD increased rapidly to highest levelafter 75 days after bolssom, and the activities of these enzymes all declined during storage.6. In order to defense low temperature and pathogen stress physiological effect, ATPcontents observably decreased. H⁺-ATPase could modulate pulp cell pH level and organic acid concentration, thus 24 hours after inoculation the activity of H⁺ -ATPase markedlyincrease, then decline constantly. Ca²⁺-ATPase activity increase rapidly and then decreasedalong with time of inoculation. Higher content of Ca²⁺ resulted in fresh dead and decayed.7. The best conditions for phytotoxin production of pear ring rot pathogen were studied.The results showed that toxicity of toxin produced in condition such as, pH value 7.5, 30℃, 10days after duration of culturing, culture medium containing PS and a little pear juice, stillcultivation under darkness. The composition of the also be determined. The ratio of protein andsugar was 69.1% and 29.6% respectively. The species of protein was single chain andpolypeptide.