柑橘之土壤傳播性真菌病害

Abstract

本省柑橘之重要土壤傳播性真菌病害包括疫病、幼苗猝倒病與細根腐敗病、流膠病、及木材腐敗病等，其中以疫病最具破壞性。危害本省柑橘之主要疫病菌共有五種，依次為Phytophthorn porositicQ , P. polmivoro , P. citrophthoro , P. citricolo 及P. cinnomomi。病菌主要危害柑橘之幼苗、根系、樹幹基部、及果實。初次感染源主要來自污染之栽培介質與灌溉用水，連續降雨與土壤濕度過高為誘發病害猖獗之重要因子。目前可行之防治策略為使用抗病或耐病品種之健康種子育苗以供為砧木，使用無病原菌栽培介質與灌溉水，苗期宜有防雨設施，注意田間排水，及藥劑防治。幼苗猝倒病與細根腐敗病由Pythium spp., Rhizoctonio Solon¡（或R. soloni like), Phytophthoro spp. 及Fusarium spp.所引起，注意育苗用栽培介質之衛生與種子消毒即可預防本病害。引起樹幹流膠之病原菌除疫病菌外，大部分為弱病原菌，分離到的有Rhizoctonio sp., Fusorium sp., Diplodio sp ., 及Phomopsis sp.等，一般在樹勢衰弱時，才會由樹皮傷口侵入感染，引起之流膠病徵與疫病菌引起者不盡相同，注意施肥、施藥、水患、及保持樹勢健旺，可預防本病害。木材腐敗病大部分由靈芝或樹舌引起，危害較少。 Phytophthora diseases, seedling damping off and fibrous root rot, gummosis, and wood rot are the important soil-borne diseases of citrus in Taiwan. Based on the frequency of isolation and pathogenicity to citrus, Phytophthora species were the most destructive fungal pathogens, and a total of 5 species including P. parasitica, P. palmivora, P. citrophthora, P. citricola, and P. cinnamomi were detected to be distributed wildly in citrus orchards. These fungi could attack seedlings, root systems, wound bark of stems, and fruit of citrus. The contaminated cultural media and irrigation water were the main sources carrying the primary inoculum, and heavy rainfall and moist soil environment were the two key factors inducing serious Phytophthora diseases. Integrated use of 1. healthy seeds, 2. resistant or tolerant root stocks, 3. disinfected cultural media or vergin soil, and pathogen free water for irrigation, 4. greenhouse or plastic sheet covering to protect young seedlings from rainfall, and 5. protective chemicals, could provide a satisfactory effect for decreasing citrus diseases caused by Phytophthora. Seedling damping off was mainly caused by Pythium spp., Rhizoctonia solani (or R. solani like), Phytophthora spp., and Fusarium spp. Sterilized or disinfected cultural mixtures and using healthy seeds cound improve seedling problems caused by these fungi. Rhizoctonia sp., Fusarium sp., Diplodia sp. and Phomopsis sp. have been isolated from the diseased barks of citrus stems with gummosis. All of the four fungi were weak pathogens which attacked weak citrus trees, and caused gummosis symptoms different from those induced by Phytophthora. Control of gummosis could be achived by enhanceing citrus trees growing stronger by avoding flooding fields and application of inadiquate ferterlizers and chemicals. Wood decay and root rot of citrus, which were occassionaly found in citrus orchard, were mainly caused by Ganoderma and Phellinus spp.