The growth of seven white clover populations differing in morphology, geographic origin, and seasonality of growth was measured at constant temperatures ranging from 5 degrees C to 25 degrees C in controlled environment chambers. All populations showed increased growth up to a maximum of 20-25 degrees C, but there were significant shifts in the relative performance of the populations at different temperatures. Leaf appearance rates, leaf sizes, and stolen extension rates were all differentially affected by temperature. Growth potential in the late winter to early spring period in the warm-temperate New Zealand climate appeared to be strongly related to the ability of plants to grow at 5 degrees C. The most rapid growing populations at 5 degrees C ('Daeno', ML-48-65) originated from continental climates. Differences of up to 21% in 2C nuclear DNA amounts were measured between the white clover populations by microdensitometry. The results were generally consistent with the prediction that large genome size is associated with capacity for growth at low temperatures, whereas small genome size is associated with superior growth at higher temperatures. The two closely-related Pitau and G49 populations were an exception to this trend.
