Adaptational Changes in White Clover Populations Selected Under Marginal Conditions

Abstract

To extend the cultivation of white clover into the marginal areas of northern Europe it is important to identify morphological and physiological characters of adaptive value. These can form the basis of selection criteria for genetic improvement. The objectives of this study were to (1) characterize the morphology of survivor populations of the white clover cultivars AberHerald and Undrom selected under Icelandic conditions; (2) investigate the growth response of selected populations in simulated spring temperatures; and (3) study how these responses affected persistence and production potential of the populations when grown under field conditions in Iceland. Results showed that natural selection had led to morphological changes in the AberHerald survivor populations in the direction of the morphology of plants adapted to the northern, marginal environment. Results obtained under simulated spring temperatures also indicated a selection for genotypes that maintained their leaf production potential. In contrast, selection in Undrom occurred for improved general efficiency and competitive ability rather than for improved survival of the harsh winter climate. The different responses of the two cultivars may partly reflect the fact that AberHerald survivors were selected after only one winter but Undrom survivors were selected after three growing seasons in experimental plots. The observed morphological changes in AberHerald were not sufficient to improve persistence when tested under field conditions. Undrom survivors, on the other hand, suffered less winter damage and showed greater production potential over the following growing season than the original population. Implications of the results for breeding white clover for marginal areas are discussed.