Effects of Wilt-Based Irrigation On Cold Hardiness of Perennial Ryegrass Genotypes.

Perennial ryegrass (Lolium perenne L.) is among the most susceptible cool-season grass to low temperature. Wilt-based (WB) irrigation is a common practice in scheduling irrigation to turfgrass as an alternative to well-watered (WW). Drought stress has been shown to promote cold hardiness but this has not been investigated in response to WB irrigation. The objective of this study was to compare the low temperature hardiness of six perennial ryegrass genotypes in response to two irrigation schedules (WW and WB). The six genotypes were selected according to turf quality ratings from the most northern NTEP location (Orono, ME) and included three top performers (All Star 2, Mach I and Sunkissed) with another three identified as bottom performers (APR-1234, Buccaneer and WVPB-R-82). Median lethal temperatures (LT50) using whole plant survival and shoot water content were measured from greenhouse samples grown in weighing lysimeters in 2007 and 2008. Plant measurements in both years were based on sampling conducted at the last cycle after 68 d of irrigation with 100% of ET applied at leaf-roll (WB) versus ET replacement every 4 d for 68 d (WW). Differences in LT50 among genotypes were only observed under WB in 2007 (-6.9 to -8.2 0C) and WUE was correlated with LT50 (r=0.88, p=0.02). Differences in LT50 were detected among genotypes under WW (-8.2 to -9.2 0C) and WB (-8.5 to -10.0 0C) in 2008. LT50 increased with shoot water (r=0.73, p=0.10) in 2008 and both were significantly lower under WB. Top-performing (TP) genotypes were able to achieve a greater degree of cold hardiness in both years in response to WB compared to bottom-performing (BP) genotypes. In 2007 and 2008, TP genotypes exhibited significantly lower LT50 temperature and shoot water content compared to BP genotypes. Irrigating perennial ryegrass using WB practices may promote acclimation to cold but these potential benefits are dependent on genotype.