Reducing the environmental impact of red clover (Trifolium pratense L.): physiological approaches underpinning germplasm improvement

Red clover (Trifolium pratense L.) is an increasingly important component of sustainable grassland agriculture and particularly organic farming. The red clover breeding programme at IGER aims to develop new varieties that are high yielding and persistent, particularly under grazing. It is also focusing on environmental traits, particularly those associated with nitrate leaching following defoliation, which is an increasingly important issue in the UK due to the recent implementation of NVZ (Nitrate Vulnerable Zones). While some of the traits
associated with forage yield can be measured in the field, those associated with environmental impact are not amenable to this approach on the large numbers of plants required for a germplasm improvement programme. An experiment has been established in flowing solution culture (FSC) to measure the response of diverse red clover selection lines to cutting, with particular emphasis on nodule senescence, a key factor in nitrate leaching after defoliation. Cutting significantly influenced the growth and development of the different lines, reduced
crown diameter and led to nodule senescence. Differences between selection lines in nodule number and nodule weight per plant after cutting were observed, indicating the existence of potentially useful genetic variation in nodule senescence. The relevance of these results for the development of improved red clover varieties for sustainable grassland agriculture are discussed.