Phytophthora Root and Crown Rot of Sage Caused by Phytophthora cryptogea in California

In 1996, commercial plantings of sage (Salvia officinalis) in the Salinas Valley in Monterey County, CA, were affected by a root and crown disease. Roots were necrotic, and crowns and lower stems turned black. Affected plants withered and died. A Phytophthora sp. was consistently isolated from roots and stems of the symptomatic plants. The species was identified as Phytophthora cryptogea based upon the formation of hyphal swellings, morphology of sporangia and oospores, and growth at cardinal temperatures (1). Pathogenicity of representative isolates was confirmed by applying 2 ml of a zoospore suspension (2.0 × 10⁵ zoospores per ml) to roots and crowns of 3-month-old potted sage plants. After treatment, plants were placed for 24 h in shallow trays of water to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 4 days, foliage of all inoculated plants began to wilt. After 7 days, plant crowns and stems turned black and the plants collapsed. P. cryptogea was reisolated and recharacterized from all plants. Control plants, which were treated with water and then handled in the same way as inoculated plants, did not develop any symptoms. The tests were repeated and the results were similar. This is the first report of P. cryptogea attacking commercial plantings of sage. The authors also detected this disease in experimental plantings of sage in Stanislaus County in 1990. Reference: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.