THE INFLUENCE OF THE RHT1 AND RHT2 ALLELES ON THE DEPOSITION AND USE OF STEM RESERVES IN WHEAT

A field experiment was undertaken with a set of near-isogenic spring wheat lines (cv. Triple Dirk) to determine the influence of the Rhi1 and Rhtl alleles on the deposition of carbon in the stem, and the subsequent use of these reserves during grain growth. The amount of dry matter stored and mobilized was estimated by the measurement of changes in masses of stem from frequent harvests. Deposition or absolute reserve was defined as the sum of the increments in mass in each segment of the large culm between the time that the segment ceased extending and the time that it reached maximum mass. The incorporation of the Rhtl and Rht2 alleles into a Triple Dirk background reduced the absolute amount of stored carbon in the stem by 35 and 39%, respectively. This was a consequence of the 21% reduction of stem height in Rhtx and Rht2 lines. Use or mobilization of reserves was defined as the sum of the decrements in mass in each segment of the large culm between maximum and maturity. The alleles did not confer an ability to mobilize more of the stored stem reserves in absolute terms, although the efficiency of use of stem reserves (i.e. use as a proportion of deposition) was higher in Rht1 than in rht or Rhtr The possible contribution of stored carbon in the stem to final grain yield was estimated to be 22, 18 and 14% in the rht, Rhtx and Rht2 lines. In these estimates, the loss of mass was adjusted by 33% to allow for respiration. It was concluded that the larger stem reserves in rhl wheats are of no real advantage under favourable environmental conditions, and may in fact be a disadvantage if the accumulation of that extra dry matter results in a reduction of sink size. © 1993 Annals of Botany Company.