Identification of Quantitative Trait Loci Controlling Large Patch (<i>Rhizoctonia solani</i> Anastomosis Group 2-2LP) Resistance in Zoysiagrass

Large patch (LP), caused by <i>Rhizoctonia solani</i> anastomosis group (AG) 2-2LP, is the most impactful disease that affects zoysiagrass (<i>Zoysia</i> spp.). Currently, there are no resistant cultivars on the market, and the only effective means of control is the application of fungicides. Breeding efforts to develop cultivars with resistance to LP would benefit from an increased understanding of the genetic control of the trait. In this study, an F₁ mapping population containing 179 progeny was developed from crosses between <i>Zoysia japonica</i> 'Meyer' (susceptible parent) and <i>Z. matrella</i> plant introduction 231146 (resistant parent). Paternal (AH) and maternal (HA) linkage maps were generated using single-nucleotide polymorphism markers developed from genotyping-by-sequencing analysis. Both AH and HA maps organized into 20 linkage groups and consist of 639 and 817 markers, respectively. LP response was evaluated across four experimental runs through collection of final disease severity, digital image analysis-derived percent incidence, and the area under the disease progress curve. All traits showed significant variance among the population, and genotype and genotype × run effects were found to be significant. Sixteen quantitative trait loci (QTLs) associated with resistance were identified, explaining 2.24 to 10.3% of the total phenotypic variance. After looking for overlap across traits, a potential LP "hotspot" was found on linkage group AH_13 (34.5 to 48.6 cM). Several resistance genes were identified near peak markers. The QTLs and associated markers identified in this study have great potential to be introgressed in breeding populations for the development of LP-resistant zoysiagrass cultivars.