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-isogenicspring wheat lines (cv. Triple Dirk) to determine the influenceof the Rht₁ and Rht₂ alleles on the deposition of carbon inthe stem, and the subsequent use of these reserves during graingrowth. The amount of dry matter stored and mobilized was estimatedby the measurement of changes in masses of stem from frequentharvests. Deposition or absolute reserve was defined as thesum of the increments in mass in each segment of the large culmbetween the time that the segment ceased extending and the timethat it reached maximum mass. The incorporation of the Rht₁and Rht₂ alleles into a Triple Dirk background reduced the absoluteamount of stored carbon in the stem by 35 and 39%, respectively.This was a consequence of the 21% reduction of stem height inRht₁ and Rht₂ lines. Use or mobilization of reserve was definedas the sum of the decrements in mass in each segment of thelarge culm between maximum and maturity. The alleles did notconfer an ability to mobilize more of the stored stem reservesin absolute terms, although the efficiency of use of stem reserves(i.e. use as a proportion of deposition) was higher in Rht₁than in rht or Rht₂ . The possible contribution of stored carbonin the stem to final grain yield was estimated to be 22, 18and 14% in the rht, Rht₁ 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 rht wheatsare of no real advantage under favourable environmental conditions,and may in fact be a disadvantage if the accumulation of thatextra dry matter results in a reduction of sink size.Copyright1993, 1999 Academic Press Triticum aestivum L., Rht genes, stem reserves, deposition, mobilization, grain growth