THE INFLUENCE OF THE RHT1 AND RHT2 ALLELES ON THE GROWTH OF WHEAT STEMS AND EARS

A field experiment was carried out with a set of near-isogenic spring wheat lines (cv. Triple Dirk) to determine the influence of the Rht1 and Rht2 alleles on the partitioning of dry matter between the developing stem and the ear. Each line was sampled twice weekly and dissected into its component above-ground parts. The rate of change of the dry mass of the individual plant organs was expressed as a proportion of the rate of change of the total plant dry mass. This ratio was used to assess the relative sink strengths of the stem and ear during crop growth. The Rht1 and Rht2 alleles reduced plant height, but increased grain yield. The greater yield was achieved through a greater grain number per ear in the Rhtl line, a greater ear number per plant in the Rht2 line, and a greater allocation of assimilate to the developing ear than to the developing stem in both Rht lines, particularly at the time of maximum stem growth (17 d before anthesis). From the earliest stages of detectable ear growth until anthesis, the ear masses per unit area of the Rht1 and Rht2 lines exceeded that of Triple Dirk (Rht). It was not possible to determine whether the Rht1 and Rht2 alleles were directly responsible for increasing grain number per ear and ear number per plant, respectively, since the increase in these components of yield could equally be explained by a greater partitioning of assimilate to developing ears and tillers caused simply by a reduction in plant height. © 1991 Annals of Botany Company.