Causes of leaf reddening in subterranean clover cultivars.

Subterranean clover (Trifolium subterraneum L.) is an important legume in dryland hill pastures in New Zealand. In this environment plants adapt to low temperatures (<10°C) through a series of physiological mechanisms, such as the foliar biosynthesis of pigments, to protect vulnerable tissues. The biosynthesis of anthocyanins is one of the most important physiological responses for cold acclimation in plants. In this study we investigated anthocyanin concentration by accessing leaf reddening in 14 cultivars from three subspecies (yanninicum, brachycalycinum or subterraneum) during winter growth. The effect of anthocyanin production on spring herbage productivity was further quantified in the field and in the glasshouse. Leaf concentration of anthocyanins increased 10-fold as a consequence of cold exposure (mean daily air temperature was below ∼7°C) in red leaves compared with green leaves. There were large cultivar differences with yanninicum ssp. cultivars having the highest leaf reddening at >60%. Lowest values were observed in 'Antas' (brachycalycinum ssp.) and 'Denmark' (subterraneum spp.) at <20% of leaf reddening. Australian subterraneum ssp. cultivars had 13% higher leaf reddening values than Italian cultivars. Leaf reddening was a temporary, cold induced, anthocyanin response that did not affect subsequent subterranean clover plant growth. [ABSTRACT FROM AUTHOR]