CUCUMBER MOSAIC CUCUMOVIRUS POPULATIONS IN ITALY UNDER NATURAL EPIDEMIC CONDITIONS AND AFTER A SATELLITE-MEDIATED PROTECTION TEST

More than 2,000 samples of weeds and cultivated crops were collected in Italy from areas where cucumber mosaic cucumovirus (CMV) epidemics occurred in 1988 and 1989. A collection of weeds was also made from fields neighboring the site of a 1989 satellite-mediated protection test of tomato. Samples were screened by molecular hybridization analyses, and CMV isolates were typed on the basis of their ability to hybridize with subgroup-specific riboprobes and with a satellite RNA-specific riboprobe. A strong relationship between CMV strain and disease type was found in tomato. The etiology of the so-called lethal necrosis syndrome was related to a helper virus belonging to the S subgroup, and a CMV strain assigned to the WT subgroup was involved in the fruit necrosis syndrome. Virus strains belonging to the WT subgroup were more widely distributed on different plant species and therefore present throughout the year, whereas those of S-type occurred more frequently from winter to early spring. Samples from weeds, celery, and melon were collected around the site of the 1989 satellite-mediated protection test. The protective strain used in that study (CMV-S) belongs to the S subgroup, and no increase in the S subgroup CMV population was observed. Specific CARNA 5 sequences were recognized either in cultivated crops or in weeds even when the helper virus was no longer detectable. A seemingly new CARNA 5 variant named Tfn-CARNA 5 was found associated with tomato fruit necrosis.