Freeze Tolerance of Nine Zoysiagrass Cultivars Using Natural Cold Acclimation and Freeze Chambers

Winter-hardiness of zoysiagrass (Zoysia spp.) cultivars is an important at- tribute throughout the biogeographical transition zone; thus, the inability to withstand freezing temperatures may limit the use of these cultivars. The objective of this research was to determine the freeze tolerance (LT50) of nine zoysiagrass cultivars grown in Raleigh, NC. Four Zoysia japonica Steud. cultivars (JaMur, Palisades, Empire, and Ultimate) and five Zoysia matrella (L.) Merr. cultivars (Pristine, Zeon, Cavalier, Diamond, and Zorro) were chosen to undergo freeze testing. Cores were taken from the field in Feb. 2008, 2009, and 2010 for the winter trials and in Apr. 2008, 2009, and 2010 for the spring trials (after green-up had occurred). The cores were subjected to freeze treatmentsof-6,-8, -10,-12,and -14 8Cin programmable freezers. After thawing, cores were placed in a 41/20 8C greenhouse to promote green-up. Cores were rated for green-up after 4 weeks on a 1 to 9 scale. Nonlinear regression analysis was used to calculate an LT50 value for each cultivar. 'JaMur', 'Palisades', 'Empire', and 'Ultimate' were no different in the winter trials with an LT50 ranging from -9.8 to 10.2 8C. Among the matrella species, 'Zeon', 'Cavalier', and 'Zorro' were no different but 'Diamond' (LT50 of -6.0 8C) and 'Pristine' (LT50 of -5.7 8C) had less tolerance to freezing than the other matrella cultivars (LT50 range from -9.7 to -9.8), suggesting lower ability to cold-acclimate in the field than the other cultivars. Shoot weights of cores werecorrelated to visual green-up ratingsfor each cultivarwith anR 2 rangefrom 0.70 to 0.99 indicating a good relationship between the green-up ratings and shoot weights.