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Wilt and Root Diseases of Asclepias tuberosa L.

Chlorosis and wilting, followed by weak flowering or death, have been occurring in Asclepias tuberosa plants grown in Israel. Roots have been rotted and tuberous roots have shown dark lesions, sometimes with sclerotia. A binucleate Rhizoctonia sp. was detected on 39% and Pythium intermedium on 23% of diseased samples. Other organisms were less prevalent. Wilting began 7 days after seedlings were inoculated with P. intermedium or the binucleate Rhizoctonia sp. or both, with disease incidence ranging from 25 to 65% and disease severity index ranging from 0.30 to 0.85 (scale of 0 to 3). Healthy tuberous roots inoculated with the binucleate Rhizoctonia sp. exhibited dry rot within 4 to 7 days, and irregular black sclerotia of the pathogen were present 2 weeks later. This is the first report of either a binucleate Rhizoctonia sp. or P. intermedium occurring in A. tuberosa.