Tolerance of Cool-Season Turfgrasses to Rapid Blight Disease

Forty-nine different cool-season grass cultivars representing 24 species were tested for their tolerance to the causal agent of rapid blight, Labyrinthula spp. Seeds of each grass were sown in 7.6-cm pots and grown in the greenhouse. Plants were watered daily with deionized water for three weeks, then with artificial sea water at a concentration of 3.5 deciSiemens per meter. Experimental design was a randomized split-plot with four replications where treatment (inoculated or non-inoculated) was the main-plot factor and cultivars were the sub-plot factor. The entire experiment was replicated twice. Bulk inoculum of five Labyrinthula isolates was prepared by growing isolates on modified serum seawater agar for four days, adding colonized agar plugs to serum broth and vortexing. Cell counts of the bulk inoculum at 1.4 × 10 5 per ml were used for each inoculation. Plants in each pot were inoculated with 1 ml of inoculum placed on leaf tissue in the form of droplets from a syringe after wounding by trimming with scissors. Plants were rated for percent of diseased foliage. A high degree of susceptibility was observed in cultivars of rough bluegrass (Poa trivialis L.), colonial (Agrostis capillaris L.) and velvet bentgrasses (Agrostis canina L.), and perennial ryegrass (Lolium perenne L.) while certain cultivars of alkaligrass (Puccinellia distans (Jacq.) Parl.), slender creeping red fescue (Festuca rubra spp. littoralis (G. F. W. Meyer) Auquier), and creeping bentgrass (Agrostis stolonifera L.) appear to have moderate levels of tolerance.