Updated: Jun 20
Authors: Eduardo Bernal and David M. Francis
Bacterial spot is a devastating disease affecting all market classes of field-grown tomato (Solanum lycopersicum) produced in humid regions. Breeding for resistance to this disease is complicated because bacterial spot is caused by four species of Xanthomonas with multiple physiological races recognized for some species. To address the challenge of breeding for resistance, we developed four processing tomato near-isogenic lines (NILs) with improved disease resistance to bacterial spot using a marker-assisted backcross breeding scheme. The four NILs, OH813A, OH804A, OH802B, and OH807C, contain different resistance quantitative trait loci (QTL) in combination with major resistance loci. NILs were evaluated for disease resistance, horticultural characteristics, and genetic similarity. Disease severity was evaluated in the field during Summer 2017 and Summer 2018 against Xanthomonas euvesicatoria, Xanthomonas gardneri, and Xanthomonas perforans. In addition, we measured yield (kg), soluble solids (Brix), pH, color uniformity, and other quality traits for each NIL and the susceptible recurrent parent, OH88119, in conventional trials. The four NILs and OH88119 were genotyped with 371 single-nucleotide polymorphism (SNP) markers spread across the genome. The NILs provided effective resistance to multiple Xanthomonas species. The resistant lines displayed production traits comparable to OH88119 and are suitable for agricultural use. Genotyping data indicated that the genetic background of these tomato lines are between 93% and 99%, similar to OH88119. The Ohio State University Crop Variety Release and Distribution Committee approved the release of this germplasm, and it will be deposited into a suitable germplasm repository.