PATHOGENICITY OF TEN ISOLATES OF APPLE CHLOROTIC LEAF SPOT VIRUS TO PRUNUS SPECIES

Abstract

Apple chlorotic leaf spot virus (ACLSV; genus Trichovirus; family Flexiviridae), one of the main viruses affecting fruit trees, can cause heavy losses to the yield of plum, prune, and apricot. For instance, virulent ACLSV strains are known to elicit severe symptoms on the leaves and fruits of apricot (butteratura or viruela). To assess the pathogenicity of this virus on a wider range of stone fruits, ten viral isolates from different geographical origins (Italy, Spain, Lebanon and Hungary) that had previously been characterized serologically and molecularly (Alrwahnih et al., 2004) were further evaluated via assays in the field. In September 2003, all isolates were inoculated by chip-budding on two cultivars each of the following Prunus species: apricot ('Cafona' and 'Bulida'), cherry ('Ferrovia' and 'Giorgia'), plum ('Black Amber', 'Florenzia', 'Stanley'), and peach ('Dixired' and 'Cardinal') with six replicates for each isolate-cultivar combination. Negative controls were included in the trial. During the four growing seasons that followed, all trees were assayed by ELISA, and foliar and fruit symptoms were recorded (in the case of fruits, controls were limited to two years). High variability was observed among the ten virus isolates, ranging from latency to induction of severe symptoms. In particular, isolates PE154, from Hungary, and PL112, from Italy, were the most severe as they induced, in both apricot cultivars, symptoms of marked vein clearing and yellow mottling on the leaves, and butteratura on the fruits. The isolate PE151 and PL110 caused vein clearing on leaves of the peach cultivar Cardinal, while the isolate APR61 caused yellow spotting on leaves of cvs. Cardinal and Dixired. The PL45 isolate caused heavy vein clearing and deformation on Dixired cultivar. Up to now, no symptoms have been observed on cherry cultivars. Most of the isolates induced discoloration and light deformation on the leaves of both plum cultivars.