Detection of Apple Chlorotic Leaf Spot Virus in Tissues of Pear Using In Situ RT-PCR and Primed In Situ Labeling

Apple chlorotic leaf spot virus (ACLSV) is the type member of the Trichovirus genus, the family Flexiviridae (Martelli et al., 1994; Adams et al., 2004) and is known to infect most pome and stone fruit tree species, including apple, peach, pear, plum, almond, cherry and apricot (Lister, 1970; Németh, 1986). ACLSV has a worldwide distribution and induces a large variety of symptoms in sensitive fruit trees (Németh, 1986; Dunez & Delbos, 1988; Desvignes & Boyé, 1989). However, In Japan, this virus is one of the causative agents of topworking disease and induces lethal decline in apple trees grown on Maruba kaido (Malus prunifolia var. ringo) rootstocks (Yanase, 1974). Other severe symptoms of stone fruit trees in Europe caused by ACLSV including bark split and pseudopox in plum, bark split in cherry, pseudopox and graft incompatibility in apricot and ring pattern mosaic in pear (Dunez et al., 1972; Desvignes & Boyé, 1989; Cieślińska et al., 1995; Jelkmann & Kunze, 1995). ACLSV has very flexuous filamentous particles, approximately 640 to 760 nm in length and consisting of a single-stranded positive-sense RNA with Mr of 2·48 x 106 and multiple copies of a 22 kDa coat protein (CP) (Yoshikawa & Takahashi, 1988).