First Report of a Blight Caused by Rhizoctonia solani on Anubias heterophylla in Italy.

Abstract

Anubias heterophylla Engler, which is used in aquariums, is a species in the Araceae family native to western tropical Africa. A few nurseries in Italy produce plants for this market. During the spring of 2002, symptoms of blight were observed on Anubias plants grown in an ebb and flow soilless media system in a nursery in Sardinia, Italy. Approximately 10% of the plants were infected. Symptoms initially developed as water-soaked, zonate lesions on the base of stems. Symptoms progressed rapidly and affected the entire plant. Eventually the plant collapsed. The growing conditions (soilless cultivation, high plant density, temperatures at 22-24°C, and 95 to 98% humidity) were conducive to disease development. Isolations from infected leaf and stem tissue on potato dextrose agar (PDA) with streptomycin sulphate at 100 mg/l consistently yielded a fungus with mycelial and cultural characteristics of Rhizoctonia solani Kühn (2). The fungus was characterized as R. solani AG-IV based on hyphal anastomosis with several AG-IV tester isolates (1). Pathogenicity tests were conducted by placing 5-day-old mycelial plugs grown on PDA at the base of healthy A. heterophylla stems and maintaining the plants in a dew chamber at 18 to 22°C. After 7 days, symptoms of basal rot were observed on stems of inoculated plants, and the entire plants were wilted. Plants not inoculated remained healthy. Rhizoctonia solani AG-IV was reisolated from all inoculated plants. The pathogenicity test was repeated. To our knowledge, this is the first report of R. solani on A. heterophylla. Since there are only a few nurseries that grow Anubias, the economic impact of the disease in Italy is minimal.