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Plant & Soil Sciences
Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
turfgrass, irrigation, wilt, cold hardiness, water use efficiency, carbon isotope discrimination
Perennial ryegrass (Lolium perenne L.) is a cool-season turfgrass susceptible to low temperature injury. Wilt-based (WB) irrigation is a common practice in scheduling turf irrigation as an alternative to well-watered (WW). Moisture stress has been shown to promote cold hardiness but this has not been investigated in response to WB irrigation. Measurements of 13C isotope discrimination (DELTA) are useful predictors of water use efficiency (WUE), drought resistance, evapotranspiration (ET) and salinity tolerance but the relevance to turfgrass cold hardiness has not been determined. DELTA analyses may enable more efficient screening protocols in breeding for improved cold hardiness. Objectives of this study were to examine perennial ryegrass genotypes in relation to cold hardiness, DELTA and WUE in response to WW and WB irrigation schedules, to compare genetic diversity between top-performing (TP) and bottom-performing (BP) perennial ryegrass genotypes, and to assess the predictive value of DELTA of for cold hardiness. Six genotypes were selected based on turf quality from the most northern NTEP location (Orono, ME) and included three TP (‘All Star 2’, ‘Mach I’ and ‘Sunkissed’) and three BP (‘APR-1234’, ‘Buccaneer’ and ‘WVPB-R-82’) genotypes. ET, yield, WUE, shoot water content, rooting potential, wilting tendency, DELTA and median lethal temperatures (LT50) using whole-plant survival 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 (WW). Lower LT50 values were generally associated with low yield, low WUE and low shoot water content, whether the result of irrigation treatment or genotypic variation. TP genotypes demonstrated significantly lower LT50 temperatures (greater cold hardiness) in comparison to BP genotypes in both years. Modest cold hardiness enhancement with WB irrigation was highest for TP genotypes. Wilting tendency and DELTA were not reliable predictors of cold hardiness, although individual TP genotypes exhibited responses distinctly different than some BP genotypes. Further research is needed to investigate the physiological mechanisms of enhanced turfgrass cold hardiness in response to moisture stress.
Jeffrey Scott Ebdon