First Report of Peronospora sparsa Causing Downy Mildew (Dryberry) of Rubus fruticosus in Mexico

Michoacan State is the largest producer of blackberries (Rubus fruticosus) in Mexico with more than 4,000 ha in production. During the rainy season of 2007 (July to September), purple, angular, vein-delimited leaf spots along the midrib and major veins were observed. Affected young fruit lost their shine, became shriveled, and later dried. Some fruit split. Symptomatic leaflets from cv. Tupy were collected from the field in Tangancicuaro and Los Reyes counties. In the laboratory, 20 detached leaflets were washed with 10% bleach for 2 min, rinsed with sterile distilled water, and placed into sterile petri dishes containing 0.5% water agar. To promote sporulation of fungi, leaflets were incubated at 17°C with a 12-h photoperiod in a growth chamber. Sporangia and sporangiophores, which developed 20 days later on the underside of the leaves, were transferred to the underside of detached healthy leaves of the same cultivar with a sterile needle, and incubated as previously described. A set of noninoculated lea...