Characterization and Incidence of Citrus Leaf Blotch Virus (CLBV) in Southern Italy

Citrus leaf blotch virus (CLBV), the type species of the new genus Citrivirus of the family Betaflexiviridae, has been associated with a bud union disorder of Nagami kumquat and calamondin scions grafted on trifoliate rootstocks. After the first report in Italy in 2007, surveys to monitor CLBV incidence were carried out in nurseries, private collections, and commercial citrus orchards with trees showing bud union disorder using biological indexing and RT-PCR. Each positive sample was analyzed by single-strand conformation polymorphism (SSCP). Samples with different electrophoretic patterns were cloned and their nucleotide sequence compared by CLUSTAL W. The results confirmed the presence of CLBV in Italy and three new sequences were deposited in GenBank. Positive samples were found only in Nagami kumquat, with 100% of the trees infected, and calamondin, with 46% of the trees infected. This lower CLBV incidence in symptomatic calamondin trees could be due to a low virus titer in this host or, alternatively, the bud union crease observed could be caused by a different pathogen or by the interaction with other biotic or abiotic factors.