Using Differentially Expressed Genes, NBS-LRR Genes, and Comparative Genetics to Identify Leaf-Spot Resistant Buffalograss.

Buffalograss [Buchloë dactyloides (Nutt.) Engelm. syn. Bouteloua dactyloides (Nutt.) Columbus] is often viewed as an exceptional low-input alternative turfgrass species due to its relatively low water, fertility, and pesticide needs.   While buffalograss is relatively free from disease, leaf spot (Curvularia inaequalis) can negatively impact turf quality when environmental conditions are conducive for disease development.  Host resistance is a viable method for overcoming resistance in the absence of fungicides, but screening for leaf spot resistance is slow since the test takes several months to complete and because it is unreliable when disease conditions are not optimal. An experiment was done to develop molecular tools to identify sources of host resistance in the absence of the grow-out test.  There are multiple methods that can be used to determine if an organism is resistant to a disease. We used data from an existing RNA-seq study, where differentially expressed genes were characterized in resistant and susceptible buffalograss in response to leaf spot. From these data, three distinct sets of molecular markers were designed and used to characterize host resistance. Genetic markers were designed to the most differentially expressed genes, differentially expressed NBS-LRR genes, which are genes that encode nucleotide-binding site leucine-rich repeat proteins that aid in pathogen recognition, and genes from distinct genomic regions when the sequencing reads were mapped to Setaria italica. These three sets of genetic markers were tested on buffalograss lines with known and unknown susceptibility to leaf spot. A greenhouse test was done to validate whether the genetic markers correctly identified the leaf spot resistance state of the plant. The methods from this study present new tools for identifying disease resistance in buffalograss and can be applied to other host-disease systems.