Variation in cold tolerance and spring growth among Italian white clover populations

Seven populations collected at different altitudes in northern Italy, two L adino breeding populations and two control cultivars (AberHerald and Grassl ands Huia) of white clover (Trifolium repens L.) were included in a series of experiments analysing: (i) levels of cold tolerance using artificial and field-based methods; (ii) relationships between these measures of cold tol erance; (iii) components of spring yield, various physiological traits, and their relationships with cold tolerance. Rates of seedling and growing poi nt mortality in the populations over winter, assessed in separate field exp eriments, were closely related ( r = 0.85). Grasslands Huia showed the high est death rates, and material originating from high altitudes the lowest. T he LT50 value, i.e., the temperature at which 50% of the growing points wou ld die, estimated by an artificial freezing test, was significantly correla ted with field-based measures of seedling ( r = 0.64) and growing point ( r = 0.84) mortality. The existence of these correlations is of potential int erest for the development of indirect selection criteria for complex and ex pensive-to-evaluate traits such as winter survival in field plots. Besides being reliable, in this study the artificial assessment was also sensitive, providing a greater degree of separation of the populations means than fie ld-based measures. Of the several physiological traits (water content, conc entrations of water soluble and total non-structural carbohydrate, and wate r soluble protein content of stolons) measured at a mid-winter sampling dat e under field conditions, the only character showing significant variation between populations was soluble protein content. There was a slight trend f or material with a higher protein content to exhibit greater field-based va lues of cold tolerance. High altitude populations tended to have low spring yields. The highest spring yield was found in one of the Ladino population s. The study identified two populations which combined, to differing extent s, cold tolerance and spring yield characteristics that would be of potenti al use in breeding for specified agronomic/climatic zones.