In August 2000, violet root rot of alfalfa (Medicago sativa L.) was observed in circular to irregular patches of alfalfa. Affected alfalfa plants turned yellow to brown in fields in the Zanjan Province of Iran. Diseased roots had a compact felt cloak of violet mycelium with white or purple strands. Samples of symptomatic roots were collected from 11 locations in the province and cultured on potato dextrose agar and malt-extract agar. The morphology of fungi isolated from pieces of alfalfa root with infection cushions from each location was consistent with Rhizoctonia crocorum (Pers.:Fr.) DC. (teleomorph Helicobasidium brebissonii (Desm.) Donk) (1). Seeds of alfalfa cv. Hamadani were sown in soil infested with inoculum of one isolate of R. crocorum prepared on a sandrye grain-water medium (20 g per pot) (2). Under 10 h of light at 22°C, destroyed taproots were evident after 8 months on 64 of 100 inoculated plants, and R. crocorum was reisolated from all 64 plants. Fifty noninoculated plants showed no symptoms. This is the first report of violet root rot of alfalfa in Iran.
References: (1) P. Roberts. Pages 157--158 in: Rhizoctonia-Forming Fungi. The Trustees, Royal Botanic Garden, Kew, UK, 1999. (2) P. G. Valder. Tran. Br. Mycol. Soc. 41:283, 1958.
