Performance of Texas bluegrass hybrids in the transition zone

Abstract

High temperature and drought may reduce quality in cool-season turfgrasses during summer in the transition zone. Texas bluegrass hybrids (HBG) are genetic crosses between native Texas bluegrass (Poa arachnifera Torr.) and Kentucky bluegrass (Poa pratensis L.) (KBG) that resemble KBG but may have greater drought and heat resistance than other cool-season grasses. The objectives of four studies were to evaluate high temperature, drought, and lower mowing height effects on HBG compared with KBG ('Apollo') and tall fescue (Festuca arundincea Schreb.)(TF, 'Dynasty'), compare their rooting characteristics, and investigate their membrane lipid molecular species compositional differences. Under high temperature (35/25°C, 14h light/10h darkness), HBG ('Thermal Blue') had greater quality and gross photosynthesis (Pg), and lower electrolyte leakage than KBG and TF in a growth chamber study. The combination of high temperature and drought (60% ET replacement) caused rapid declines in quality, but HBG generally performed better. In field and greenhouse studies, TF had more roots deeper in the profile than two HBG ('Reveille' and Thermal Blue) and KBG under well-watered conditions. In the field, quality and Pg were greatest in TF among turfgrasses. Performances in quality and Pg generally ranked: TF > Reveille >= Thermal Blue = KBG. In a separate mowing height and drought field study, HBG (Thermal Blue) generally had lower quality and Pg than KBG at both high (7.62 cm) and low (3.81 cm) heights but particularly at the low height. Drought resistance and tolerance to low mowing in Thermal Blue was similar to or poorer than in KBG. Under supra-optimum temperature (35 /25°C and 40 /30°C, 14h light/10h darkness), the ratio of digalactosyldiacylglycerol (DGDG) to monogalactosyldiacylglycerol (MGDG) was highest in HBG (Thermal Blue) and lowest in TF. Heat tolerance was also associated with higher phosphatidylethanolamine (PE) content, higher phosphatidylglycerol (PG) content, and reduced overall unsaturation compared with heat-sensitive. Results suggest that 40 membrane lipid molecules are potential biomarkers for heat tolerance and that compositional changes in lipids in response to heat may contribute to differences in heat tolerance among cool-season grasses. Generally, studies indicated greater heat resistance, but not drought resistance, in HBG than in KBG or TF.