Temperature responses and nuclear DNA amounts of seven white clover populations which differ in early spring growth rates

The growth of seven white clover populations differing in morphology, geogr aphic origin, and seasonality of growth was measured at constant temperatur es ranging from 5 degrees C to 25 degrees C in controlled environment chamb ers. All populations showed increased growth up to a maximum of 20-25 degre es C, but there were significant shifts in the relative performance of the populations at different temperatures. Leaf appearance rates, leaf sizes, a nd stolen extension rates were all differentially affected by temperature. Growth potential in the late winter to early spring period in the warm-temp erate 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 deg rees C ('Daeno', ML-48-65) originated from continental climates. Difference s of up to 21% in 2C nuclear DNA amounts were measured between the white cl over populations by microdensitometry. The results were generally consisten t with the prediction that large genome size is associated with capacity fo r growth at low temperatures, whereas small genome size is associated with superior growth at higher temperatures. The two closely-related Pitau and G 49 populations were an exception to this trend.