Experiments were conducted in the glasshouse and the field to assess the phosphorus-use efficiency, yield, and yield components of several spelt wheat genotypes in comparison with standard bread wheats. Spelt genotypes had much lower grain yield than standard bread wheats, in both a well- watered glasshouse and three field situations. The reduction in yield was often as great as 60% and was largest in late-flowering spelt genotypes. Spelt genotypes responded to increasing amounts of applied phosphorus (P) fertiliser, adequately acquired P from soil, and some had higher total amounts in their tissues; however, these P reserves were not as efficiently converted into grain yield as standard bread wheat cultivars, primarily due to the growth of tall, unproductive tillers, and lower kernel number and kernel size. There was no evidence of spelt yielding better than common wheat under conditions of P-deficiency. There is great potential to breed improved spelt genotypes through relatively simple modification of yield components and phenology, but whether this can be achieved while maintaining the grain quality attributes valued highly by the organic industry remains to be seen. Breeding for improved spelt should target reduced height and tiller number, early flowering, and larger kernels.

Keywords: phosphorus-use efficiency, spelt, grain yield, tillering, wheat.