| Apple Alternaria Blotch was one of the apple early defoliation diseases, whichoccured in much apple production areas in china. Apple Alternaria Blotch could infectnew shoots and fruits of apple, thus infulunced the growth and flower bud formationof apple tree, and caused early defoliation.When the disease epidemiced, disease ratewas about70%, seriously restricted the development of apple industry in Gansuprovince.1. In this research two apple Alternaria blotch pathogens A1and A2, isolatedfrom different apple production areas in Gansu province, were identificated in speciesby the morphology and molecular biology method.Through the morphology study anddetermination of pathogenic symptom, preliminarily determined strains A1and A2were Alternaria mali. The ITS sequence analysis has confirmed that A1and A2were100%similar with Alternaria mali. Therefore, determined the strains A1was highvirulence strain of A.mali and caused apple altemnaria blotch, and A2was lowvirulence strain of A.mali and caused ring spot of apple.2. In this research the pathogenicity of two strains of A.mali on apple leaves weresdutied by spray inoculation method at different conditions. The results showed thatthe incubation period was shorter and occurring degree was obviously higher of highvirulence strain than low virulence strain at different temperature, relative humidityand light conditions. When temperature was30℃, the incubation period of two strainsof A.mali were the shortest, among them, the high virulence strain of A.mali wererespectively54hrs, and low virulence strain of A.mali were72hrs. When thetemperature was25℃, the disease index of high virulence strain of A.mali had amaximum which was23.06. When conditions were continuous lighting after UVirradiation3hrs, the disease index of low virulence strain of A.mali had a maximumwhich was21.24. There were obvious differences in resistances of different applevarieties against two strains of A.mali, Fuji and Starkrimson were resistant variety,Golden Delicious was susceptible to two strains of A.mali. Low virulence strain of A.mali showed obvious cross protection effects to high virulence strain of A.mali, andcould reduce the infection by high virulence strain of A.mali.3. The high virulence strain of A.mali was mutated by ultraviolet lights andmicrowave irradiation in this test. The results showed that when the doses ofultraviolet mutagenic were power for10W, irradiation distance for10cm and time for5min, the A.mali happened negative mutation, and pathogenic was lowest, the sporegermination rate is only58.45%after6hrs, the quantities of spore production, hyphagrowth and the colony diameter were respectively2×104/ml,152.67mg and3.67cmafter4d, and incidence rate and disease index were respectively38.50%and10.32after7d. When the dose of microwave irradiation were power for700W and time for60s, The biological activity of A.mali mutants was lowest, pathogenicity have aminimum, the spore germination rate is only1.83%after6hrs, the quantities of sporeproduction, hypha growth and the colony diameter were respectively4×104/ml,139.30mg and3.83cm after4d, and incidence rate and disease index wererespectively31.94%and7.87after7d. Therefore, ultraviolet mutated for5min andmicrowave irradiated for60s could be used for best conditions that made the A.malihappened negative mutation and pathogenicity decreased.4. The inhibitory and resistant effect against A.mali, and the contents of diseaseresisitence substances of apple leaves were determinated after induced by differentconcentrations of Salicylic Acid and Chitosan through spraying method in thisexperiment. The results showed that different concentrations of Salicylic Acid andChitosan had no significant inhibitories effect against A.mali. The concentrations of100μg·mL-1(Salicylic Acid) and500μg·mL-1(Chitosan)had the lower percentages ofinhibition, and the inhibition rates were only5.33%and4.73%, respectively. But theinduced-resistance effects were more significantly, they were as high as70.90%and77.77%, respectively. The activities of POD, PAL and the content of lignin weresignificantly higher than control, and with the increased of time, the POD and PALactivities increased at first and then decreased, the maximum of two enzymesactivities were at3days after induction. The activity of PPO had an increased trend with the time increased induced by Chitosan, but the effect of Salicylic Acid to PPOactivity was not significantly. |
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