Explaining Late Blight Lineages

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Late blight is a disease that we deal with to some extent in the mid-Atlantic each year and there have been some recent reports in the area (MD, NJ) over the last few days. When reports come in you may see something mentioned about the lineage that was detected. US 23? Isn’t that a highway?

Each lineage has unique genetic characteristics that may impact management practices and also level of concern in the region. Some lineages prefer to cause disease on potatoes, some tomatoes, and some both. In addition, some are sensitive, intermediate, or insensitive to mefanoxam fungicides. As a quick reference, you can view the recent lineages reported in the United States at the USAblight website http://www.usablight.org/node/52. I have simplified the information for you below.

Genotype Host Sensitivity to mefenoxam
US-8 Potato I/R
US-11 Potato/Tomato R
US-20 Tomato I/R
US-21 Tomato S/I/R
US-22 Potato/Tomato S/I
US-23 Potato/Tomato S/I
US-24 Potato I

Source USAblight.org: Summary of multilocus genotypes of Phytophthora infestans collected in the US and Canada, 2002-2009 (from Hu et al., Plant Dis. 2012 and Fry et al., APSnet Features 2012)