Evaluation of Zoysiagrass Cultivar Relative Susceptibility to Rhizoctonia Solani AG -2-2 LP.

Evaluation of Zoysiagrass cultivar relative susceptibility to Rhizoctonia solani AG -2-2 LP

N. Flor (1), K. Kenworthy (1) and P. Harmon (2)

(1) Agronomy Department, (2) Plant Pathology Department, University of Florida, Gainesville, Fl, USA

Zoysiagrass (Zoysia spp.) is a commonly used warm season turfgrass in the United States. Large patch is the major fungal disease caused by Rhizoctonia solani anastomosis Group 2, subgroup 2, strain Large Patch (AG 2-2-LP). Severe infections result in significant decreases in turf quality. Older zoysiagrass cultivars have been evaluated for their response to Rhizoctonia solani; however, there are newer cultivars that have yet to be screened. Therefore, in 2010, 12 cultivars of Zoysia spp. were inoculated with a virulent isolate of the fungus (UF0714) to observe their responses. Each cultivar was propagated into 7.6 cm diameter pots with 12 replications each and grown in a greenhouse maintained between 25°C and 45°C with approximately 80% RH.  The grass was trimmed to four cm height biweekly.The experiment was completed twice using three- and six-month-old plants. In each trial, six plants of each cultivar were inoculated using 15 wheat seeds that were infested with the fungus, and six plants with sterilized seeds  as controls. Each pot was enclosed in 1 gallon sealable plastic bag and maintained in a growth room with these settings: 23°C (day), 21°C (night), 85% RH and 12-h photoperiod. Disease severity ratings were taken at seven and 14 days after inoculation (DAI) using a modified Horsfall-Barratt scale. Mean disease severities among cultivars were separated using a Duncan test (P ≤ 0.05).  Data from both experiments were combined. All cultivars developed disease, but significant differences in severity were observed. At seven DAI, ‘Empire’, ‘Jamur’ and ‘El Toro’ exhibited less disease than other cultivars tested. At 14 DAI, mean disease severity of all cultivars were greater than 48 percent, with ‘Zorro’ (87 %), ‘Emerald’ (83.2%), ‘Pristine’ (82.7%) and ‘Shadow Turf’ (80.5%) having the greatest disease. Results indicated that these methods successfully identified relative differences in cultivar disease responses to Large Patch.