Performance and adaptability of subterranean clover pure lines and line mixtures of different complexity across contrasting Mediterranean environments

Abstract

Abstract Earlier investigations on the possible advantages of heterogeneous inbred crops in terms of performance, adaptability and yield stability focused mainly on small-grain cereals. This study provides an unprecedented assessment of these advantages for an inbred forage crop, namely, subterranean clover (Trifolium subterraneum L.). Pure lines of the subspecies subterraneum (S) and brachycalycinum (B) featuring contrasting phenology that were collected from each of two climatically-contrasting locations were compared with their intra-subspecies 2- and 4-component mixtures and inter-subspecies 4- and 8-component mixtures. The comparison encompassed biomass yield, seed production and seedling regeneration measured over two seasons in four managed environments with contrasting soil types and drought stress levels. Compared with the mean value of component lines, intra-subspecies mixtures of the subspecies with greater phenological diversity, i.e., S, exhibited greater biomass, seed yield and seedling regeneration across environments, whereas intra-subspecies mixtures of B or inter-subspecies mixtures with 4-components exhibited a biomass yield advantage only. Diversity maximisation by the 8-component mixture failed to out-yield the mean of its component lines for any trait. On average, mixtures diplayed distinctly greater stability of biomass yield and seedling regeneration performance as measured by low absolute values of the first entry × environment interaction principal component axis compared to pure lines. Advantages were similar for the two subspecies and tended to increase with increasing mixture complexity. While S mixtures could capitalise on complementary responses of their component lines to different drought stress levels, inter-subspecies mixtures could also exploit complementary responses to contrasting soil types. The comparison among best-performing entries within each plant material highlighted the value of a B 2-component mixture, which displayed a slight, non-significant penalty of biomass yield, nearly identical seed yield and seedling regeneration, and distinctly greater stability of performance for all traits, compared to the pure line with greatest biomass yield.