Cherry Chlorotic Rusty Spot: Description of a New Viruslike Disease from Cherry and Studies on its Etiologic Agent

Abstract

A novel cherry disease that has been observed in southern Italy is characterized by chlorotic leaf spots that later develop a rusty appearance, small and deformed fruits with color alterations, and tree decline. We propose to call it cherry chlorotic rusty spot disease. The disease spreads naturally in the field, but the vector is not known. A bacterial or fungal etiology is unlikely based on testing that indicates the probable involvement of a virus- or viroidlike agent. In agreement with this hypothesis, 12 double-stranded (ds) RNAs and one or two small, circular RNAs have been consistently isolated only from symptomatic cherry plants. The pattern of dsRNAs is reminiscent in its complexity, but not in the size of the components, of that characteristic of phytoreoviruses. This pattern could also be produced by the genomic and subgenomic dsRNAs resulting from the infection of one, or a mixture of more than one, single-stranded RNA virus. The close association in symptomatic tissue between the small, circular RNAs and the dsRNAs suggests that the former could be viroidlike satellite RNAs rather than autonomously replicating viroids, although definitive conclusions must await infectivity bioassays.