Studies On Distribution Of Apple Scab In Province And Infection Characteristic Of Venturia Inaequalis

Apple scab, caused by an Ascomyccete fungus, Venturia inaequalis, was regarded as one of the most important disease of apple and was found in practically all apple-growing regions throughout the world. It mainly damaged leaf and fruit and could result in defoliation and poor fruit value, and the extra cost for controlling was included also. Even though apple scab was the internal quarantine disease, it was expanded to most apple growing areas in Shaanxi province. Distribution of this disease in main apple-growing regions of Shaanxi was found by field investigation, which showed that apple scab existed throughout the Guanzhong plain and north part of apple growing areas. The percentage of diseased leaf in the north of QingLin Mountains was round 10.67‰, which was the heaviest, and it reached significant difference from those of other four areas. The west Weibei plateau and the west Guanzhong plain were 7.57‰and 6.13‰respectively and there was no significant difference of that between them. The east Guanzhong plain and East Weibei plateau regions were 2.13‰and 0.17‰respectively. The percentage of diseased leaf made great difference among the different cultivars, which was Gala>Fuji>Red Star>Qinguan. The cultivars of Fuji and Gala, most popularized in Shaanxi Province, were susceptible to apple scab. According to the conidia and its percentage of germination of Venturia inaequalis in/outer buds, the type and the number of the trapped spores and the temporal dynamic of the percentage of diseased leaf in 3 different orchards in north of Weibei and combined with extensive investigation in Luochuan, Baishui, Changwu, Rongshou, Jinchuan, Pingliang et al., the result indicated that the resource of the first infection came from ascospore of V. inaequalsi and conidia didn't overwinter in those areas. Incubation period of apple scab and the number of sporulation of Venturia inaequalis were studied. Results indicated that the incubation period of Gala, Fuji and Qinguan were 11.1, 13.2 and 15.7 days respectively. Temperature had great effect on incubation period. The incubation period of apple scab was the shortest at 18℃of per-day average temperature. The number of Sporulation on leaves of Gala, Fuji and Qinguan were 2.8263×104, 7.4168×103, 1.1465×103 conidia /mm2 respectively, which showed significant difference(a= 0.05). 18 isolates collected from 12 counties or cities were inoculated and the pathogenicity was determined on cultivars of Qinguan, Fuji, Gala, Red Star and Jonagold, which the pathogenicity showed significant difference among those isolates. According to the infect type and average severity, 18 isolates were classified into strong pathogenecity type, including PD2, GB1, NC3, YC4, moderate, including LC1, PA7, JYC1, FD6, XYB2, PB3, XD4, SC4, XC8, NB8 and weak, including HC3, XYD5, JYA6, CD7. The standard parameter of infection type and severity were determined respectively.