Phytotron Evaluation of Zoysiagrass Germplasm for Large Patch Resistance.

Large patch, caused by Rhizoctonia solani Kuhn, is a common disease of warm-season turfgrasses. When the disease is actively developing, large areas of turf can be severely damaged.  Among warm-season turfgrasses, Zoysiagrass is one of the most susceptible ones to the disease. Plants often sustain serious damage and recovery can take several weeks or months.  There are several fungicides available for control of the disease, but they must be applied on a preventative basis.  Development of cultivars with genetic resistance to the fungus is the most effective means for management of large patch. The present study was conducted to screen 17 cultivars, five plant introductions, and 88 accessions from the North Carolina State University (NCSU) germplasm collection of Zoysiagrass for resistance to Rhizoctonia solani.  The experiment was conducted at the Southeastern Environment Laboratory (Raleigh, NC) under controlled environmental conditions. Plants were inoculated with winter oat seeds that had been colonized by the fungus. Disease severity was estimated seven and 14 days after inoculation (DAI) using the Horsfall-Barrat rating system. Disease coverage ranged from five to 55%. Cultivars ‘Cavalier’, ‘Zorro’, and 'Royal' were found to have the highest levels of resistance. Several accessions from the NCSU collection and one plant introduction displayed comparable levels of resistance.