Studies On Pathogenicity Of Botryosphaeria Dothidea And Evaluation Technology Of Fungicides For Controlling Apple Limb Ring Rot

Apple ring rot is one of the main diseases on apple, can cause severe loss of apple andoccurs widely, and has become an obstacle to influence sound development of appleindustry. Several problems remain to be solved, such as too many registered fungicides, theconfusion in production application, lack in effective evaluation and resistancedevelopment to fungicides exists in control of the disease. The evaluation technology wasconstructed through petri-dishe experiments, twig test experiments and field experiments.The purpose of this study is to evaluate the control efficacy of fungicides registed andprovide useful information to fruit growers. The research results are as follows:1. The pathogenicity of isolates of Botryosphaeria dothidea was compared on applefruit, twigs of4-year-old apple trees. The pathogenicity of isolates from the same area wasdifferent. There was correlation between pathogenicity on fruits and pathogenicity on twigsof4-year-old trees. Difenoconazole、propiconazol and thiophanate-methyl were used astopical wound trearments to the controlling effects to extension of stem cankers caused byB. dothidea. These fungicides could consistently reduce the incidence of the disease andsize of cankers compared with the water control. But B. dothidea were frequently isolatedfrom xylem tissue, suggesting that fungicides could not prevent the development of thepathogens. The cankers on Wang Lin were smaller than on Fuji, but Mato1with resistance,cankers were similar to which on Fuji.2. Through test of fungitoxicity of10fungicides, we found that10%difenoconazoleWG,45%propiconazole ME,400g/L flusilazole EC and80%tebuconazole WP, hadsignificant inhibitory activity effect on mycelial growth with EC50of0.0092μg/mL,0.0443μg/mL,0.3977μg/mL and0.5880μg/mL, respectively. Four fungicides, including80%mancozeb WP,45%amobam AS,50%iprodione WP and250g/L azoxystrobin SChad strong inhibitory effect on spore germination, with EC50of0.3572μg/mL,0.3649μg/mL,0.4327μg/mL and0.7683μg/mL, respectively.3. Through the modified dual culture assays, the inhibitory effects of10fungicides onmycelial growth were tested. The results showed that80%carbendazim WP had the highest inhibitory effect. The fungistatic belt was3.617cm, followed by45%propiconazole ME and80%tebuconazole WP.4. In the twig tests,70%thiophanate-methyl WP（875mg/L）and80%carbendazimWP（1333mg/L）totally stopped the infection of the pathgen. In the curative effect test, thecontrol effect of400g/L flusilazole EC,80%mancozeb WP and45%propiconazole MEwere87.48%、73.04%、71.83%, respectively.5. Comprehensive analysis of the fungitoxicity effects of10fungicides againstBotryosphaeria dothidea, protective effect and the curative effect on the detached twigs,10fungidides were ranked together again.400g/L flusilazole EC,80%Tebuconazole WPwere recommended to control apple limb ring rot by using them in combination withscraping disease tumor. Because conidium were spread by the rain, protective fungicides50%iprodione WP,70%Thiophanate-methyl WP were suggested to spray before therainfall in summer.