Widmer T L, Graham J H, Mitchell D J
Former Graduate Assistant, Department of Plant Pathology, University of Florida, IFAS, Gainesville 32611.
Professor, Citrus Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, 700 Experiment Station Road, Lake Alfred 33850.
Plant Dis. 1998 Jun;82(6):683-688. doi: 10.1094/PDIS.1998.82.6.683.
Most citrus nurseries and orchards in Florida are infested with Phytophthora nicotianae, the causal agent of Phytophthora root rot. Although fungicides control the disease and increase seedling growth and tree yields, they are not always economically or environmentally sustainable. Amendment of citrus soils with composted municipal waste (CMW) may provide an alternative to fungicides for disease management. Citrus seedling growth decreased with increasing proportions of one CMW source, indicating the potential for phytotoxicity from soluble salts and acetic acid when the proportion of CMW in soil exceeded 20% (vol/vol). When a citrus soil was amended (20% vol/vol) with certain sources of CMW, the incidence of infection of 5-week-old susceptible citrus seedlings by P. nicotianae was reduced from 95% to as low as 5%. Addition of fresh CMW to two different citrus soils reduced colony growth of P. nicotianae after the fungus was incubated in the amended soil for 6 days and then recovered on PARPH selective medium. If CMW was stored for more than 3 months before amendment, the soil mixtures did not suppress colony development. In general, extracts of fresh CMW reduced mycelial growth in vitro; whereas suppressiveness of CMW from the same batch was lost after storage. Acetic acid was detected at higher concentration in fresh CMW that suppressed colony growth than in CMW that lacked activity. A species of Acremonium was isolated from another source of CMW that was suppressive to P. nicotianae. This fungus parasitized hyphae of P. nicotianae in vitro. Thus, CMWs have the potential to at least temporarily suppress P. nicotianae through chemical and microbial agents depending on source and age of the CMW.
佛罗里达州的大多数柑橘苗圃和果园都受到烟草疫霉的侵染，烟草疫霉是柑橘根腐病的病原体。虽然杀菌剂可以控制这种病害并提高幼苗生长量和树木产量，但它们在经济或环境方面并不总是可持续的。用堆肥化城市垃圾（CMW）改良柑橘土壤可能为病害管理提供一种替代杀菌剂的方法。随着一种CMW来源比例的增加，柑橘幼苗生长量下降，这表明当土壤中CMW的比例超过20%（体积/体积）时，可溶性盐和乙酸可能产生植物毒性。当用某些来源的CMW改良柑橘土壤（20%体积/体积）时，5周龄易感柑橘幼苗被烟草疫霉感染的发生率从95%降至低至5%。向两种不同的柑橘土壤中添加新鲜CMW，在真菌在改良土壤中培养6天然后在PARPH选择性培养基上恢复后，可减少烟草疫霉的菌落生长。如果CMW在改良前储存超过3个月，土壤混合物就不会抑制菌落发育。一般来说，新鲜CMW的提取物在体外可减少菌丝体生长；而同一批次的CMW储存后抑制活性丧失。在抑制菌落生长的新鲜CMW中检测到的乙酸浓度高于无活性的CMW。从另一种对烟草疫霉有抑制作用的CMW来源中分离出一种顶孢霉属真菌。这种真菌在体外寄生于烟草疫霉的菌丝。因此，根据CMW的来源和储存时间，CMW有潜力至少通过化学和微生物因子暂时抑制烟草疫霉。
