Characterizing the growth and cold hardiness of Zoysia spp.

Zoysiagrass (Zoysia spp.) is a warm-season grass well-adapted to lawns and golf turfs that requires minimal inputs. Key barriers to widespread zoysiagrass use are slow establishment rate and poor cold hardiness. Therefore, my objective was to determine the physiological basis for differences in growth and cold hardiness of zoysiagrass. Field studies first quantified differences in establishment rate and winter injury among zoysiagrass cultivars and the underlying factors associated with differential growth rates and freeze tolerances were examined in ensuing growth/freeze chamber studies. Mean establishment rate and coverage in field studies were greater for Zoysia japonica Steud. than Z. matrella (L.) Merr. \u27El Toro\u27, \u27Chinese Common\u27 and \u27Palisades\u27 were among the cultivars that produced more coverage than the mean whereas the industry standard \u27Meyer\u27 produced less coverage than the mean. Growth analysis indicated cultivars that partition more dry matter to stems instead of leaves establish the quickest. Zoysia japonica cultivars had less winter injury than Z. matrella cultivars. Meyer, Chinese Common and \u27Zenith\u27 exhibited the least winter injury (\u3c6%) among commercially available cultivars, whereas \u27Victoria\u27, \u27DeAnza\u27, \u27Diamond\u27, and \u27Empress\u27 had the most winter injury (\u3e88%). Freeze tolerance (LT50) of cold acclimated plants, as determined using a cold stress simulator, ranged from -8.4°C (Diamond) to -11.5°C (Meyer and Zenith). SDS-PAGE indicated that cultivars had similar polypeptide composition irrespective of cold acclimation. However, immunoblotting indicated that dehydrin polypeptides increase during cold acclimation and a 23 kDa dehydrin polypeptide played a role in improving freezing tolerance. Starch, glucose, total reducing sugars and proline concentrations in cold-acclimated plants were correlated (r = 0.61, -0.76, -0.62, and -0.62, respectively) with LT50. Additionally, the change in sugar:starch ratio and total soluble sugars during acclimation were correlated with LT50 ( r = -0.66, and 0.55, respectively) indicating that the decrease in starch during cold acclimation is more important to improved zoysiagrass freezing tolerance than increased soluble sugars. Results suggest that certain dehydrins, higher concentrations of glucose, total reducing sugars and proline improve zoysiagrass freeze tolerance whereas higher concentrations of starch are detrimental