Studies On Pathogen Identification And Control Techniques Of Fruit Ripe Rot Of Kiwifruit In Fengxin County

For the purpose of ascertaining which kinds of fungi cause fruit ripe rot of kiwifruit, Fungi were isolated from a large number of rotten fruit, and the isolated fungi were identified by morphological characteristics, pathogenicity test and nucleotide sequence analysis. The results showed that six kinds of fungi were responsible for fruit ripe rot of kiwifruit in Fengxin Connty. They are Botryosphaeria dothidea, Botryotinia fuckeliana, Pestalotiopsis sp., Fusarium proliferatum, Phomopsis sp., and Alternaria sp. In which, Botryosphaeria dothidea is the dominant pathogen having 83.0% of isolation rate, and next is Phomopsis sp. having 8.9% of isolation rate.Biological characteristics of main pathogens (Botryosphaeria dothidea and Phomopsis sp.) of fruit ripe rot of kiwifruit were studied in order to provide basic information for inhibiting mycelium growth of pathogen and controlling the disease. The results showed that the pathogens of fruit rot have potential pathogenicity on a variety of fruit crops. The pathogens of kiwifruit fruit rot could grow between 5℃ and 35℃, and the most optimum temperature was 25℃. The best media for their growth was PDA, CA and AEA, and the optimum pH was 7. For mycelial growth of the pathogens, the optimum carbon sources were sucrose, dextrose, maltose and cellose, and the optimum nitrogen sources were yeast extract, beef extract and peptone.B. dothidea and Phomopsis sp. are the two main kinds of pathogenic fungi causing fruit ripe rot of kiwifruit in Fengxin County, Jiangxi province. Indoor toxicity test of six fungicides against the two kinds of fungi by using mycelial growth rate method was carried out. The results showed that five fungicides of 75%Trifloxystrobin-Tebuconazole, 50% Iprodione,10%Difenoconazole,70%Thiophanate-Methyl and 60% Pyraclostrobin-Metiram were strongly toxicant to both B. dothidea and Phomopsis sp. The EC50 values of five fungicides to B. dothidea were in turn 0.1439μg/mL,0.1502μg/mL, 0.1795μg/mL,0.2640μg/mL and 0.9466μg/mL, and to Phomopsis sp. were in turn 0.0893μg/mL,0.2228μg/mL,0.1320μg/mL,0.4034μg/mL and 0.7922μg/mL. Fungicide 50%Kresoxim-Methyl, however, had very low toxicity to the two fungi, and the EC50 values of it to B. dothidea and Phomopsis sp. were 7890.7μg/mL and 12881.0μg/mL, respectively.The control technique of kiwifruit fruit ripe rot were systematically studied for effective control its occurrence regularity. The result showed that the three kiwifruit varieties of ’Harward’,’Yunhai-1’ and ’Jinyan’ were highly resistant to fruit rot pathogen of kiwifruit, best control period of kiwifruit fruit ripe rot before mid-August, control efficiencies as high as that of 75%Trifloxystrobin-Tebuconazole and 25%Pyraclostrobin, orchard cleaning and bagging on fruit rots of kiwifruit in the field. The control efficiencies of soaking the fruit in fungicide liquid were the lowest.The pathogen causing gray mold and fruit stem blight on kiwifruit in Fengxi Countyof Jiangxi province was identified as Botrytis cinerea (teleomorph Botryotinia fuckeliana) and Glomerella septospora by morphological characteristics, pathogenicity test and sequence homology analysis of the rDNA-ITS, the pathogenic fungus can normally grow in 5～30℃, and penetrate fruit of kiwifruit only through wound infection. Following identification of the pathogen, toxicity tests of dirrerent fungicides to Botrytis cinerea and Glomerella septospora were carried out in laboratory by using mycelium growth rate methods, the results showed 75%Trifloxystrobin·Tebuconazole,43%Tebuconazole and 25%Pyraclostrobin had higher inhibition effect to the pathogen.