百香果白星病菌微循環分生孢子之病原性與化學防治

Pathogenicity of microcycle conidia and chemical control of Septoria blotch of passion fruit

百香果（Passiflora edulis Sims）的果實可供鮮食、加工等多種用途，是重要的經濟果樹。Septoria passifloricola Punith感染百香果嫁接苗，造成葉部白星病，容易引起落葉，減少嫁接苗的存活率。本研究評估溫溼度對白星病菌分生孢子發芽能力的影響，結果顯示24-28℃及相對溼度97%為最適合分生孢子發芽的條件。發現該真菌於液態培養下可進行微循環產孢，產生大量分生孢子，將微循環產生之分生孢子接種於百香果切離葉，結果顯示，接種於傷口處理葉之近軸面及遠軸面，及無傷口處理葉之遠軸面皆可產生病徵；接種於經傷口處理的植株葉片上亦可引發病，顯示微循環產生的分生孢子為具傳染性的繁殖體。評估S. passifloricola對登記使用於百香果之殺菌劑的敏感性，發現對三氟派瑞、百克敏、亞托待克利及克熱淨等較敏感，遂選用進行溫室藥劑防治試驗，結果顯示三氟派瑞及亞托待克利之防治效果最佳，接種前及接種後施用殺菌劑無顯著差異；其次為百克敏於接種後施用亦有相近的防治效果。

"Passion fruits (Passiflora edulis) have high economic values because the fruits could be consumed in multiple ways such as fresh fruit or food processing. Septoria passifloricola frequently causes leaf blotches on grafted seedlings of passion fruits at nursery, resulting in defoliation and reduction of survival. Here, the effects of temperature and relative humidity on conidial germination of S. passifloricola isolates PLS-S2 and PLS-R were evaluated. The optimal conditions of conidial germination were at 24-28℃ and ≧97% of relative humidity. It was found that S. passifloricola could undergo microcycle conidiation in submerged cultures and generate abundant conidia. The microcycle conidia were able to produce symptoms at detached leaves when inoculated on adaxial and abaxial surfaces of wounded leaves and abaxial surface of unwounded leaves. Symptoms were also induced by microcycle conidia on wounded leaves attaching on plants. These results suggest that microcycle conidia are infectious propagules. The screening of fungicide sensitivity indicated that isolates PLS-S2 and PLS-R were sensitive to pyraclostrobin, fluopyram + trifloxystrobin, azoxystrobin + difenoconazole, and iminoctadine triacetate. The four fungicides were assayed in greenhouse trials. The fluopyram + trifloxystrobin and azoxystrobin + difenoconazole were the most effective on the control of Septoria blotch of passion fruit, and their applications before or after inoculation were no significant difference. The application of pyraclostrobin after inoculation was also effective."