Timmer L W, Zitko S E, Gottwald T R, Graham J H
Professor.
Senior Biologist, University of Florida, Citrus Research and Education Center, Lake Alfred 33850.
Plant Dis. 2000 Feb;84(2):157-163. doi: 10.1094/PDIS.2000.84.2.157.
Sporadic epidemics of Phytophthora brown rot occur in citrus orchards in Florida and are caused primarily by Phytophthora palmivora and secondarily by P. nicotianae. With P. palmivora, fruit wetness durations of 3 h or more resulted in maximum infection at favorable temperatures. The optimum temperature range for fruit infection and brown rot development was 27 to 30°C. No brown rot developed at 22°C or less. The optimum temperature for sporulation in culture and on the fruit surface was 24°C, with sporangium production decreasing rapidly at higher or lower temperatures. A few sporangia were produced with 18 h of fruit wetness, and numbers increased as duration of wetness increased up to 72 h. Propagules were splash-dispersed by single droplets of water from infested peel disks horizontally about 350 to 450 mm and vertically about 30 to 45 mm with most isolates. Sporangia were not dispersed by air currents alone. Few sporangia of P. nicotianae were produced on fruit surfaces, and they were not readily dispersed by falling water droplets. Brown rot caused by P. palmivora can become epidemic in Florida from July to October during the rainy season because of its high temperature optimum and prolific sporulation on the fruit surface.
疫霉褐腐病的零星流行发生在佛罗里达州的柑橘园中，主要由棕榈疫霉引起，其次是烟草疫霉。对于棕榈疫霉，在适宜温度下，果实湿润持续3小时或更长时间会导致最大感染率。果实感染和褐腐病发展的最适温度范围是27至30°C。在22°C或更低温度下不会发生褐腐病。在培养基和果实表面产孢的最适温度是24°C，在较高或较低温度下孢子囊产量迅速下降。果实湿润18小时会产生一些孢子囊，随着湿润持续时间增加到72小时，孢子囊数量会增加。对于大多数分离株，繁殖体通过受侵染果皮盘上的单个水滴飞溅传播，水平传播约350至450毫米，垂直传播约30至45毫米。孢子囊不会仅通过气流传播。烟草疫霉在果实表面产生的孢子囊很少，并且它们不容易被下落的水滴传播。由于棕榈疫霉的最适温度较高且在果实表面产孢量大，由其引起的褐腐病在佛罗里达州7月至10月的雨季可能会流行。
