Effect of Hot-Air Treatment on Likubin. Tristeza Virus and Exocortis Viroid Diseases of Citrus

Abstract

Buds from likubin diseased citrus trees were grafted to rangpur lime seedlings. They were exposed to alternate temperatures of daytime ca. 40℃ for 16 hr and nighttime 30℃ for 8 hr for a period of 4 weeks or longer, such treated plants produced no likubin symptoms in new growth after two-year period of observation. All treated plants indexed in mexican lime seedlings showed tristeza virus symptoms. These results indicated that the main component of likubin pathogen was inactivated, hut the tristeza virus was not completely inactivated. Young shoots from tristeza-infected mexican lime seedlings which had been placed at 40/30℃ for 15 weeks or 39-45/29-33℃ for 10 weeks could he free from tristeza virus. Temperatures at 38/28℃ was not sufficient for virus inactivation. None of hot-air treated cuttings were free from exocortis pathogen even the treatment was prolonged up to 52 weeks. 以感染柑桔立枯病之病穗芽接於二年生建全廣東檸檬幼苗上，每天給於照光16小時40℃/無照光8小時30℃之交替溫度處理，經過四週或較長時間處理後，新生枝條均呈現健全，顯示熱處理已將立枯病病原不活化。但若採取此等植物之植株經墨西哥雷木檢定，則可發現有Tristeza virus之有在。由是可知。，立枯病主要病原比Tristeza virus較易於利用熱處理而使之不活化。 感染Tristeza virus之墨西哥雷木幼苗，同樣置於 40/30℃之交替溫度處理，經過3至4週後，新生雷木葉片上Tristeza病徵被抑制，但病毒仍然存在。病植物繼續處理，經過十週，尚未使病原不活化，但延長至15週，則採取之嫩穗，大部份已無Tristeza。溫度越高，處理效果越佳，時間亦可縮短，如在39-45/29-33℃之溫度下處理病植物10週後，即可獲得無Tristeza病之嫩穗。在植38/28℃下，雖然處理時間長達20週，對Tristeza乃然無效。Exocortis病原對熱抵抗性很強，病物雖然處理時間長達一年，切取之嫩穗乃含有其病原。