Physiological Changes Associated with Wilt‐Induced Freezing Tolerance among Diverse Turf Performance Perennial Ryegrass Cultivars

Abstract

ABSTRACTPerennial ryegrass (Lolium perenne L.) is a cool‐season turfgrass susceptible to low temperature injury. Wilt‐based irrigation (WI) is a common practice for scheduling irrigation to turf by allowing a mild, negative water imbalance to occur as an alternative to maintaining turf under nonlimiting soil moisture. Moisture stress has been shown to promote freezing tolerance but this has not been investigated in response to WI. Objectives of this study were to examine perennial ryegrass in response to WI (applied at 50% visual leaf roll) on freezing tolerance (median lethal temperature at 50% survival [LT50]), 13C discrimination (Δ), internal leaf‐to‐ambient CO2 concentration (ci:ca) ratio, leaf water, rooting, water use efficiency (WUE), and wilting tendency (days to wilt and number of wilt events) among three top‐performing (TP) and three bottom‐performing (BP) perennial ryegrass cultivars. Cultivars were selected based on turf quality trials from a northern location (Orono, ME). Plant measurements were made in the greenhouse in 2007 and 2008 comparing the first (single) and last (multiple) wilt cycle after 68 d of irrigation between well watered and WI. Multiple wilt exposures significantly enhanced freezing tolerance compared to a single wilt event for TP cultivars only, but gains in freezing tolerance were small (<1.0°C). Freezing tolerance (lower LT50 values) was generally associated with lower yield, WUE, and leaf water content. In some TP cultivars, wilt‐induced freezing tolerance was associated with greater wilting tendency and drought sensitivity indicated by lower Δ values and ci:ca ratio. Repeated wilt exposures increased rooting over a single wilt event.