Disease Note

Witches’ Broom Disease of Alfalfa in Saudi Arabia. A. A. Cook, Regional Agricultural and Water Research Center, Ministry of Agriculture and Water, Riyadh, Saudi Arabia. A. C. Wilton, Regional Agricultural and Water Research Center, Ministry of Agriculture and Water, Riyadh, Saudi Arabia. Plant Dis. 69:83. Accepted for publication 26 September 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-83B.

Alfalfa (Medicago sativa L.), especially varieties developed in the Middle East, is widely planted in Saudi Arabia as the major forage crop. Witches’ broom disease, characterized by numerous frail stems with small leaflets on plants much reduced in size, is found throughout the kingdom and is believed to be the reason for excessive stand reduction leading to early termination of plantings in many areas. The causal agent, presumed to be a mycoplasma, was transmitted via dodder (Cuscuta campestris Yuncker) to periwinkle (Vinca rosea L.). In a replicated trial of 24 alfalfa varieties planted in November 1982, the incidence of diseased plants per visual counts averaged 15% (1,059 of approximately 15,600 plants). Plots of Middle Eastern varieties contained more infected plants than did those of American varieties. Fewer (<1%) CUF 101 (California) plants became infected than any other variety planted.