ROOT AND SHOOT DRY-MATTER PARTITIONING IN NEAR-ISOGENIC WHEAT LINES DIFFERING IN HEIGHT

Increased wheat (Triticum aestivum L.) yields in most major cereal gro wing areas of the world have been associated with shorter cultivars wh ich incorporate the Rht1 or Rht2 height-reducing alleles. Considerable uncertainty still exists, however, concerning the growth of vegetativ e tissues, especially roots, of these shorter genotypes. The objective of this study was to determine how dry matter (DM) partitioning, in v egetative shoot and root tissues, is related to plant height as determ ined by the number of Rht alleles present (tall (no Rht alleles), semi dwarf (Rht1 or Rht2), dwarf (Rht1 and Rht2) within a common genetic ba ckground. Tall, semidwarf, and dwarf near-isogenic lines were studied within each of four diverse genetic backgrounds. Six controlled-enviro nment experiments were carried out in which plants were grown in sand (nutrients applied hydroponically) and harvested following anthesis. S tem and shoot (total aboveground tissue) DM plant-1 increased with pla nt height. However, there was no relationship between plant height and root DM plant-1. Root/shoot ratios tended to be negatively correlated with plant height. Leaf blades and head DM plant-1 were not consisten tly related to plant height. In the absence of selection pressure, gen otypes containing Rht alleles should have root DM comparable to their tall counterparts, and root/shoot ratios equal to, or greater than, th eir tall counterparts. The Rht alleles also decreased individual leaf blade areas, primarily through effects on leaf length, and increased s tomatal frequencies of early leaves; effects on the flag and penultima te leaves were ambiguous, suggesting that the gibberellic acid (GA3) i ntensitive Rht alleles exert greater control during earlier growth sta ges.