Effects of several fungicides on controlling apple Phytophthora rot caused by Phytophthora cactorum

Abstract:【Objective】Apple Phytophthora rot, caused by Phytophthora cactorum(Leb. et Cohn.) Schrot,is an important disease on apple fruit in China. The disease caused fruit decays, reduced the yield and reduced the income of apple orchards. In order to screen effective fungicides, protective and systematic effects of 13 fungicides on controlling apple Phytophthora rot were tested on detached fruits by applying the fungicides before and after inoculated with zoospore suspension of P. cactorum.【Methods】The pathogen of P. cactorum was isolated with CA mediums from Phytophthora rot fruits, sampled from an orchard in Jincheng town, Laizhou city, Shandong province in July, 2013. Mycelia of the isolates were cultured in V8 mediums for 3-4 days, in V8 liquid mediums for 3 days and in sterilized water for 2 days to induce zoosporangia. Zoospore suspension was made by placed the zoosporangia in 4 ℃ for 1-2 hours. Fresh‘Fuji'apple fruits, sampled from July to October from an orchard never applying fungicides in the growth season,were used for the fungicide test. For the protective effects, fungicides with the recommended dosages by the manufactorys were sprayed to fresh apple fruits with a hand sprayer. At the time of 1, 3, 5 and 10 days after applying fungicides, the fruits were taken out and inoculated by spaying zoospore suspension. The inoculated fruits were immediately put into several boxes with saturated humidity(RH=100%). The boxes were sealed and transferred into an incubator with temperature set to 25 ℃. Three fruits were inoculated for each fungicide at each time. Lesion number was recorded after the fruits showed symptoms. For systematic effects, the fruits were firstly inoculated by spraying zoospore suspension, then put into boxes with sat-urated humidity and incubated at 25 ℃ for 24 and 72 hours. The fruits were taken out and sprayed with fungicide and then put back to the boxes for further incubations. Three fruits were sprayed for each fungicide at each time. The percentage of lesion area on each fruit were recorded when the lesion number no longer increased. ANOVA was used to compare the different significance in protective and systematic effects of the 13 fungicides with control【.Results】Examined at the 15 day after inoculation in the protective effect test, the average number of lesion per fruit inoculated one day after applying fungicides were 2.08 for the water treatment(control) and zero for the 13 fungicides treatments. The protective effects of the 13 fungicides were 100%. Lesion number per fruit inoculated three days after applying fungicides were 2.42 for control, 0.6, 0.13 and 0.07 for Hymexazol, Propamocarb Hydrochloride and Cymoxanil mancozeb, respectively; and zero for the other 10 fungicides. When inoculated at 5 day after spraying fungicides, lesion number were 1.65 per fruit for control, 0.53 and 0.64 for Hymexazol and Propamocarb Hydrochloride,which didn't show significant with the control, and zero or near zero for other 11 fungicides. When inoculated at 10 day after applying fungicides, lesion number were 1.63 per fruit for control, and zero for the 6fungicides, which were Fluopicolide-propamocarb, Oxadixyl mancozeb, Dimethomorph, Cyazofamid, Pyraclostrobin and Mandipropamid. Examined at the 11 day after inoculation in the systematic effect test, the average percentage of lesion area per fruit sprayed water(control) were 42.88% and 62.31% for the treatments applyed fungicides at 24 h and 72 h after inoculation respectively. Lesion areas were between18.33% and 40.83% for the 13 fungicides when applied at 24 h after inoculation, which didn't show significant difference with control. Lesion area were between 26.39% and 61.67% for the 13 fungicides when sprayed at 72 h after inoculation, which didn't show significant difference as well.【Conclusion】All of the tested fungicides can effectively protected the fruits and prevented the pathogen infection when applied before the pathogen infection, but can't effectively inhabit pathogen extension and prevent the infected fruits from showing symptoms when applied after the pathogen infection. The protection effects of Fluopicolide-propamocarb, Oxadixyl mancozeb, Dimethomorph, Cyazofamid, Pyraclostrobin, Mandipropamid and Cymoxanil mancozeb can last for more than 10 days.