Natural Occurrence of Phytophthora infestans on Black Nightshade (Solanum nigrum) in Wales

There is only one published record of natural infection of black nightshade (Solanum nigrum L.) by Phytophthora infestans (Mont.) de Bary in England (3) and none from Wales. In August 2001, brown, necrotic leaf lesions with pale green margins were found on black nightshade weeds in a potato trial naturally infected with P. infestans at Henfaes Research Centre, University of Wales, Bangor. Although the plants were low growing with large, succulent leaves 4 to 5 cm long instead of having a more erect habit and smaller leaves, their identity was confirmed as S. nigrum; their atypical appearance may relate to the known phenotypic plasticity of this species (4). Infected leaflets incubated in moist chambers produced sporangia typical of P. infestans, and zoospores were released after chilling in water. Five isolates obtained from leaf fragments had growth on rye agar that was indistinguishable from that of P. infestans from potato. Detached leaflets of S. nigrum and S. tuberosum cv. Green Mountain inoculated w...