Cold hardiness of saltgrass accessions

Freezing tolerance is an environmental adaptation that significantly influences plant geographical distribution. Since differences in winter survival among saltgrass ecotypes have been observed in the field at Fort Collins, CO, the objective of this study was to determine the relative freezing tolerance, seasonal changes in the freezing tolerance, and winter survival of six accessions of saltgrass [Distichlis spicata var. stricta (L.) Greene]. Saltgrass accessions A65 and A29 were originally collected from Denver, CO, while C66 was from Humbolt Sink, NV, 32 from Wanship, UT, 55 from Hereford and 48 from Farmingdale, SD. These accessions were established in a field nursery at Fort Collins, CO. Rhizomes were sampled at monthly intervals from October 1999 through April 2000 and from October 2000 through April 2001 and subjected to laboratory freezing tests. Cold hardiness of the saltgrass accessions increased gradually during the fall with maximum hardiness occurring at midwinter. During midwinter, freezing tolerance was significantly different among accessions. Ranking of accessions for subfreezing temperature resulting in 50% mortality [LT 50 (°C)] during January 2000 was A29 = 48 (-20.0) < 55 (-17.0) ≤ 32 (-15.5) ≤ A65 = C66 (-14.0). In January 2001, they were ranked with 48 = 55 (-26.0) < A65 = 32 (-23.0) < A29 (-20.0) = C66 (-18.5). In December and January sampling dates of the first season, accessions A29, 48, and 55 exhibited the highest relative regrowth when exposed to temperatures -20.0°C. In midwinter of the second season, accession 55 showed the highest regrowth after being subjected to temperatures -25.0°C. Accession C66 had the lowest regrowth potential after freezing treatments in both seasons. Winter survival in the field correlated negatively with LT 50 value, with accessions 48, A29, and 55 demonstrating greater winter survival while C66 had the lowest percentage survival. The difference in freezing tolerance among accessions is in part associated with their origin-inherited adaptation. This information is useful for defining the potential adaptation range of saltgrass and in saltgrass breeding projects to select and develop freezing tolerant saltgrass.