GENOTYPIC VARIATION FOR COLD TOLERANCE IN WINTER AND FACULTATIVE BARLEY

Improved winter survival of barley (Hordeum vulgare L.) may be achieved by developing genotypes that maintain an acceptable level of cold tolerance despite fluctuations in air soil temperature. The cold tolerance of eight winter and facultative barley cultivars, a spring barley and a winter wheat (Triticum aestivum L.) was measured in controlled freeze tests of field-grown material. The temperature lethal to 50% of each genotype population (LT50) was calculated from survival data. The LT50 values for each genotype were determined at multiple sampling dates at two locations over a 2-yr period. Sampling dates were considered environments and these data were used to identify genotypes showing stable, or full-season, cold tolerance. Genotypes were grouped according to patterns of comparable LT50 response across the six environments. The significant genotype group X environment interaction detected in the analysis of groups and environments was due to changes in magnitude of response rather than changes of rank. Averaged across all environments. 'Norstar' winter wheat was significantly more cold tolerant than the barely germplasm, and there was little variation for cold tolerance among winter barley genotypes. Winter barley cultivars were more cold tolerant than facultative cultivars. Two joint regression stability parameters, the regression coefficient (b) and squared deviations from regression (s(d)2), revealed genotypic variation for full-season cold tolerance.