Virulence and oospore potential of novel Phytophthora infestans clonal lineages on potato, tomato and solanum weeds

Authors: SANCHEZ-PEREZ, AMILCAR - University Of Wisconsin; Halterman, Dennis; GEVENS, AMANDA - University Of Wisconsin

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: The oomycete Phytophthora infestans is a widely distributed phytopathogen and is the causal agent of late blight of potato and tomato. This pathogen was a key factor in the Irish Potato Famine, which occurred around 160 years ago and still remains a problematic disease in modern agriculture when potato and tomato are grown under cool and humid environmental conditions. Late blight can cause severe economic losses in commercial potato on agriculture by reducing the yield, storability, and by the cost of fungicides and their application. The use of resistant cultivars is an important component of an integrated late blight disease management program for both potato and tomato, and often the most economical and friendly with the environment and human health. However, only a limited number of potato cultivars with late blight tolerance are commercially available. Phytophthora infestans has two mating types called A1 and A2. When the two opposing mating types interact in or on infected leaves, stems, fruits, or tubers, thick-walled, soil persistent oospores can be produced. The objectives of this study were to evaluate new strains of P. infestans isolated from tomato and potato in Wisconsin on different varieties of potato and tomato which previously were reported to have some resistance to late blight. We also evaluated the ability of these varities to allow oospores formation in the leaves and stems after pathogen inoculation. Our results will impact late blight resistance breeders as well as scientists interested in late blight resistance characterization and disease epidemiology through the identification of varieties that allow or prevent oospore formation.

Technical Abstract: The oomycete Phytophthora infestans is a widely distributed phytopathogen and is the causal agent of late blight of potato and tomato. Late blight can cause severe economic losses in commercial potato on agriculture by reducing the yield, storability, and by the cost of fungicides and their application. The use of resistant cultivars is an important component of an integrated late blight disease management program for both potato and tomato, and often the most economical and friendly with the environment and human health. P. infestans is a heterotallic organism, which has two compatibility groups termed mating type A1 and A2. When the two opposing mating types interact in or on infected leaves, stems, fruits, or tubers, a thick-walled, soil persistent oospores can be produced. In 2009 and 2010, both mating types were isolated from samples collected from infected tomatoes and potatoes in Wisconsin, although mating pairs were not collected from individual fields. The objectives of this study were to evaluate new strains of P. infestans isolated from tomato and potato in Wisconsin on different varieties of potato and tomato which previously were reported to have some resistance to late blight. We also evaluated the ability of these verities to allow oospores formation in the leaves and stems after pathogen inoculation. We found that new clonal lineages of P. infestans are virulent on potato cultivars Satina, Defender and Jacqueline Lee, which were previously reported as resistant. Tomato carrying Ph-2/Ph-3 resistance genes and potato and tomato plants with the RB resistance gene showed resistance to the three new clonal lineages evaluated in this study. Furthermore, plants containing RB did not allow formation of oospores in plant tissues.