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A PCR assay for Verticillium dahliae race 1 resistance in lettuce based on genome sequencing of 60 resistant or susceptible cultivars

Patrik Inderbitzin: University of California at Davis, Department of Plant Pathology

<div><em>Verticillium dahliae </em>is a soilborne plant pathogen that is a major threat to lettuce production in the Salinas and Pajaro Valleys of central coastal California. In tomato, resistance to <em>V. dahliae </em>race 1 is conferred by <em>Ve1</em>, which encodes a nucleotide binding-leucine rich repeat receptor (NLR) protein. There are two copies of <em>Ve </em>in tomato, <em>Ve1 </em>and <em>Ve2</em>, but only <em>Ve1 </em>provides resistance to <em>V. dahliae</em>. In the <em>V. dahliae</em> race 1-resistant lettuce cultivar La Brillante, there are three <em>Ve </em>homologs, <em>Verticillium resistance</em> <em>1 </em>(<em>Vr1</em>), <em>Vr2</em> and <em>Vr3, </em>which are 54 - 57% similar to <em>Ve1 </em>in tomato<em>.</em> Three <em>Vr</em> paralogs are also present in the <em>V. dahliae </em>race 1-susceptible cultivar Salinas, and it is currently unknown which of the <em>Vr </em>paralogs confers resistance to <em>V. dahliae </em>race 1 in lettuce. To develop a PCR assay to detect <em>V. dahliae </em>race 1 resistance in lettuce, we sequenced the genomes of 60 resistant or susceptible lettuce cultivars and extracted the <em>Vr </em>gene-like sequences, and found that the La Brillante <em>Vr1</em> allele (<em>LBVr1)</em> was present in all resistant cultivars, and absent in all susceptible cultivars. This indicated that <em>LBVr1 </em>is associated with resistance of lettuce to <em>V. dahliae </em>race 1. We designed a <em>LBVr1</em>-specific PCR assay and validated its accuracy on an additional 90 accessions. This work indicates that <em>LBVr1 </em>may be the functional <em>Vr </em>allele in lettuce. Gene knock-out assays are underway to prove the function of <em>LBVr1 </em>in resistance to <em>V. dahliae </em>race 1.</div>