Zoysia spp.: Adaptability and Possible Use in the Mediterranean Environment.

ABSTRACT Pompeiano, Antonio Ph.D., Pisa University and Sant’Anna School of Advanced Studies, September, 2009. Zoysia spp.: Adaptability and Possible Use in the Mediterranean Environment. Major Professor: Sergio Miele. In today’s climate, in which economic and environmental sustainability has to be ensured, it is important promote alternative grass species that require minimal maintenance inputs. The excellent heat and drought tolerance of zoysiagrass (Zoysia spp.) made it an excellent choice for Mediterranean areas. Key barriers to widespread zoysiagrass use are slow establishment rate and lack of cold hardiness. My first objective was to evaluate the adaptation and performance of ten genotypes of Zoysia spp., assessing differences in establishment rate, winter color retention, and biometric traits. It was observed differences in total stolon length and stolon growth rate among the genotypes, and for all stolon growth parameters, Z. japonica as species had significantly the highest values compared with Z. matrella. A clear distinct trend in days to 50% color retention was observed in this study on winter color retention of genotypes. Difference between Z. japonica genotypes were observed, with ‘DeAnza’, ‘El Toro’, and above all, ‘Victoria’ (respectively 57.2, 57.8, and 77.6 Days50) retained green color better than ‘Meyer’ value. Zoysia japonica genotypes exhibited poor color retention (50.3 Days50) compared to Z. matrella (L.) Merr. genotypes (79.3 Days50). An additional field study was carried out by transplant of single potted plants obtained from sprigs and raised in peat-filled honeycomb alveoli. This innovative establishment technique is considered a viable alternative to the more traditional warm-season turfgrass establishment techniques (stolonizing or plugging). At the University of Arkansas, a greenhouse study was conducted to determine the effect of ammonium and nitrate as nitrogen source on zoysiagrass (Zoysia spp.). A slow-growing and a fast-growing cultivar of each species {‘El Toro’ and ‘Meyer’ [Z. japonica Steud.], ‘Diamond’ and ’Zorro’ [Z. matrella (L.) Merr.]} were assessed for growth analysis, root architecture, and color. Results of growth analysis indicate Z. japonica genotypes prefer solution with 1 NO3- : 3 NH4+ ratio, on ‘Zorro’ a similar result was recorded, whereas no specific trend for dry matter yields of whole plants was observed on ‘Diamond’. Nitrate has been shown to cause a suppression in root growth, regardless the species. Changes in nitrate : ammonium ratio produced distinctive differences on root morphology. Surface area and root volume were promoted by prevalent ammonium treatments in Japanese lawngrass, while a lack of consitency in the patterns was observed in Manilagrass. A field trial was conducted to assess the effects of late-season N application, and timing on color retention of Z. matrella (L.) Merrill cv ‘Zeon’. This study shows that application dates play critical roles in plant response to prolong fall and winter color. No winter injury was observed in any plots the following spring regardless of the late-season N application date. Delaying N application is effective in maintaining acceptable color up to mid January. Additionally, a study was performed with the principal aim of assessing development of freeze tolerance (LT50) of ‘Zeon’ zoysiagrass under the effect on two different levels of late-season nitrogen applications compared with an untreated control, and the dynamic of nonstructural carbohydrate composition and reserve are altered during cold acclimation and overwintering. During the experiment time, significant differences in response of treatments to the freeze test were found. In October, as expected, the higher N treatment was significantly less cold hardy (LT50 = -10.0°C) compared to the other treatments, but it results to be beneficial to freeze tolerance in March. The control reached its cold hardiness in November, 1 month earlier than the N treatments and in agreement with the color retention data. It showed a more linear freeze tolerance during experiment time. Significant variations in total soluble sugars occurred in leaves, stems, roots, and sprigs during acclimation and de-acclimation process. Alteration of metabolism was more evident in the 30 g N treatment, in particular in the storage sink.