柑橘黑點病之田間發病消長

Disease Incidence of Citrus Melanose in Taiwan

人工吊掛黑點病菌保菌枝條情況下，石碇桶柑、關西及嘉義柳橙自抽春梢、結小果、果實肥大期，延續至11月上旬皆可發病；惟嘉義7月份較不利發病，11月以後發病減少。石碇桶柑及關西柳橙田間自然發病情形，在春梢、5月的果實發病皆見增加，6月持續發病，7月底、8月初發病減低，8月中旬以後發病又增加，10、11月份則呈平緩。8月以前呈前期感染病徵，9月以後呈後期感染病徵。春梢、小果的發病度與成熟期的果實發病度間呈正相關，夏、秋梢與果生實發病度相關係數則未達顯著。調查北部地區柑橘樹冠內枯枝產生孢子角的情形，在5月以前未見形成，5月以後持續至年底皆有孢子角之溢出；而每個月份皆可發現地上的柑橘枯枝中含有子囊殼，且形成率極高。

In artificial inoculation experiment, the pathogen attacked citrus plants at young leaf stage and the growth period of fruit from March to November. At Chiayi citrus orchard where melanose never occured, a significant higher melanose severity was produced on inoculated fruits during the fruit growth period except from July to August because of temperature factor. A survey on the disease incidence was carried out at Shutien and K wanshi in 1985. The period of more disease incidences were found in Shutien and K wanshi during March to June and August 11 to October, but only rare melanose lesion appeared during July to August 10. Two symptom types were differentiated according to the infection period. Higher positive correlationship was found among the disease incidence of spring shoots, young fruit, and mature fruit stages. Fruiting pycnidium on the citrus dead twigs within the citrus canopy was as abundant as those falling over on soil surface from May to December. Perithecia are abundant on those dead twigs falling over on soil surface at any time around the year. These facts may require a modification of control practices for the citrus melanose in the areas where the perithecia stage is significant.