Poster Session: Genetics of Resistance

296-P

Late blight resistance in heirloom and hybrid tomato cultivars against the US-22, US-23, and US-24 clonal lineages of Phytophthora infestans.
A. C. SEIDL (1), A. J. Gevens (1)
(1) University of Wisconsin, Madison, WI, U.S.A.

Phytophthora infestans causes late blight, an important disease of tomato worldwide. Resistance genes are known, but few cultivars with effective resistance are commercially available. Using detached leaves, we tested 11 tomato cultivars for resistance to 3 current clonal lineages, US-22, US-23, and US-24. Lesion length and percent mycelial cover were plotted separately against days post inoculation and area under each curve was analyzed. Pooling the lineages, 3 heirloom cultivars with no known resistance genes, Matt’s Wild Cherry, Wapsipinicon Peach, and Pruden’s Purple exhibited lesion lengths not significantly different (NSD) than Mountain Magic (contains Ph-2 and Ph-3 resistance genes). Analysis of mycelial cover gave similar results and indicates the utility of these cultivars for mitigating disease impact and secondary inoculum production. ‘Plum Regal’ (Ph-3) had lesion lengths NSD than ‘Mountain Magic’ when inoculated with US-23, but lesion lengths NSD than the most susceptible cultivar when inoculated with US-22 and US-24. Differential disease responses of cultivars to novel clonal lineages indicates a continued need to evaluate the effectiveness of tomato cultivars against current P. infestans populations. Identification of resistance in heirloom cultivars to 3 common lineages of P. infestans indicates that there are available and perhaps underutilized sources of resistance for breeding and that these cultivars can be used to lessen reliance on fungicides.