First Report of Phytophthora Root and Crown Rot of Penstemon Species. F. E. Brooks, Department of Plant Pathology, University of California, Riverside 92521. D. M. Ferrin, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 79:212. Accepted for publication 6 December 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0212C.
Phytophthora root and crown rots are a problem on many California native plants grown in cultivation, but have never been reported on Penstemon spp. (Scrophulariaceae). Cultivars of six different species of Penstemon (n = 22) were planted in a newly constructed Cultivar Garden at the Rancho Santa Ana Botanic Garden, Claremont, CA, between June and December 1991. The first symptoms of disease were observed 6 mo after planting and by August 1992 all of the plants exhibited stunting, leaf discoloration, wilt, root and crown rot, or plant death. Phytophthora ciirophthora (R. E. Sm. & E. H. Sm.) Leonian was isolated from the roots and soil surrounding one of the cultivars, P. labrosus 'Bashful.' To confirm pathogenicity, three experiments were conducted. Millet seeds colonized by P. ciirophthora were buried in the potting mix surrounding 8-wk-old Penstemon seedlings. Plants were then flooded every 3 days. After 14 days, leaf discoloration and wilting were observed on most plants and by day 21 all inoculated plants were wilted and had root and crown rot. No plants in potting mix with sterile millet seeds exhibited these symptoms. The pathogen was reisolated from necrotic roots and crowns and again identified as P. ciirophthora.