First Report of Artichoke Downy Mildew Caused by Bremia lactucae in Argentina

In 1999, downy mildew was detected on artichoke (Cynara scolymus L.) plants from La Plata, Buenos Aires Province. The disease was observed on various commercial varieties. Symptoms were angular interveinal chlorotic spots less than 3 cm in size. These infected areas, although not confluent, covered a wide surface and caused early death of the leaves. On the undersides of these lesions, white-grayish sporulation was abundant, consisting of sporangiophores with dichotomous branches, widened in their peaks with 2 to 7 terminal sterigmata. Sporangia were ellipsoidal, hyaline and 14 to 30 × 12 to 25 μm in size. Oospores were not observed in leaf tissues. The pathogen was identified as Bremia lactucae Regel (1). Pathogenicity was confirmed with the inoculation of healthy artichoke plants. They were incubated in a humidity chamber at 10 to 15°C, and after 16 days chlorotic spots and downy mildew colonies developed. The presence of B. lactucae was confirmed by macro- and microscopic observation and Koch's postulates were fulfilled. This is the first report of downy mildew on artichoke in Argentina. Because it is widespread in the most important artichoke-growing area in Argentina (2), downy mildew should be considered in the cultural and sanitary management of the crop. References: (1) P. Corda. Hypermedia Prot. Plantes, INRA, 1995. (2) A. Ricceti et al. Bol. Hortic. 4:4, 1996.