Epidemiological importance ofSolanum sisymbriifolium,S. nigrumandS. dulcamaraas alternative hosts forPhytophthora infestans

Abstract

Lesions ofPhytophthora infestanswere found on woody nightshade (Solanum dulcamara), black nightshade (S. nigrum) andS. sisymbriifoliumduring a nationwide late blight survey in the Netherlands in 1999 and 2000. Pathogenicity and spore production ofP. infestansisolates collected from potato (S. tuberosum),S. nigrum,S. dulcamaraandS. sisymbriifoliumwere determined on several host plant species, and oospore formation in naturally infected and inoculated foliage of hosts was quantified. The present population ofP. infestansin the Netherlands is pathogenic onS. nigrum,S. dulcamaraandS. sisymbriifolium. Oospores were produced in leaves ofS. nigrum,S. dulcamaraandS. sisymbriifoliumfollowing infection with A1 and A2 isolates. Therefore these plant species should be regarded as alternative hosts for the late blight pathogen. In the case ofS. nigrumandS. dulcamarainfection was a relatively rare event, suggesting that diseased plants do not significantly contribute to the overall late blight disease pressure present in potato‐production areas. Oospore production in ageingS. nigrumandS. dulcamaraplants in autumn, however, may generate a considerable source of (auto) infections in following years. Considerable numbers of sporangia and oospores were produced onS. sisymbriifoliumfollowing infection withP. infestans. Additional field infection data are needed to evaluate the epidemiological consequences of a commercial introduction ofS. sisymbriifoliumas a potato cyst nematode trap crop.