Phosphorus responses of Trifolium pallescens and Trifolium occidentale, the progenitors of white clover (Trifolium repens)

Context: Rock phosphate reserves are decreasing, and requirements to mitigate environmental impacts of farming soils with excess phosphorus (P) are increasing. Aims: White clover is an allotetraploid hybrid between Trifolium pallescens and T. occidentale. Understanding the P response characteristics of these progenitor species will allow selection of germplasm for development of synthetic white clovers with improved phosphorus-use efficiency (PUE). Methods: Shoot and root weights and P nutrition characteristics were compared for three Trifolium pallescens, six T. occidentale accessions, and a white clover cultivar in a glasshouse experiment using a low P soil amended with five rates of P. Key results: White clover had the highest and most P responsive shoot and root dry weights (DW), and T. pallescens was least responsive to P. In the highest P treatment, T. pallescens had the highest shoot and root %P and the lowest shoot DW:total plant P ratio. There was significant variation among progenitor accessions. Spanish accessions of T. occidentale had comparable shoot DW to white clover and higher PUE. Traits of T. pallescens indicated strong adaptation to low P but low productivity, while traits of T. occidentale were more aligned with the white clover cultivar. Conclusions: The substantial variation in P nutrition characteristics within the progenitor species of white clover could be exploited in breeding programs. Implications: Comparing the P responses of a wider range of progenitor accessions could inform breeding to improve white clover’s low soil P tolerance through development of synthetic white clovers.