Further Studies on the Complex Causing Likubin of Citrus in Taiwan H. J. SU and T. MATSUMOTO LIKUBIN

LIKUBIN has been prevalent in Taiwan since 1958, attacking most of the commercial varieties such as ponkan, tankan, and sweet orange. Formerly thought to be due to unfavorable soil conditions, such as high moisture content and deficiency of essential nutrients, or to root rot, it was subsequently demonstrated to be caused by an infectious agent believed to be closely related to tristeza virus because it induced the tristeza reaction in West Indian lime and Eureka lemon and was transmitted by the tropical citrus aphid Toxoptera citricidus Kirk. (9, 10). The tristeza virus from likubin was, however, found to differ somewhat from that in other countries; it affected ponkan rooted on sunki, Cleopatra mandarin, and Troyercitrange rootstocks, which are reported to be resistant to tristeza virus in North and South America. Aeglopsis chevalier; also indexed positive with the virus. Moreover, positive reactions in lime seedlings were obtained by grafting them with scions from healthy looking ponkan and tankan trees on sunki rootstock. Because of these discrepancies, it was assumed that some unknown component, in addition to tristeza virus, was associated with likubin. This paper reports the results of investigations made to identify the unknown component and to clarify the nature of the complex.