Epidemiological aspects of garlic decline disease caused by a phytoplasma in Asiatic and Argentinean garlic cultivars

Garlic decline is a disease that has been detected in most of the garlic-growing areas of Argentina. The associated pathogen has been identified as a 16SrIII-group phytoplasma. Little is known, however, about epidemiological aspects of the disease. Incidence and prevalence of the disease were analysed during 3 consecutive years in fields of an Asiatic garlic cultivar (Chino) and two Argentinean cultivars (Blanco and Colorado) from the principal garlic-growing areas of Argentina. Although low incidence was registered (0.03–0.78%), disease prevalence was high in both sampled regions (23–100% fields had at least one diseased plant). Cultivars Chino and Blanco were more susceptible to the disease since incidence and prevalence were significantly higher than in cv. Colorado. The pathogen was detected by polymerase chain reaction (PCR) in a high proportion of cloves from infected plants and in plants derived from potentially infected cloves, showing that the phytoplasma can be transmitted from a crop cycle to the following by planting infected cloves. The phytoplasma was detected by transmission electronic microscopy, PCR and dot blot immunoassay in all parts of the symptomatic plants, and the highest pathogen concentration was found in root tissues. Although 22 leafhopper species were found associated with the garlic crop, insect populations were low during the whole crop cycle.