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

Increased wheat (Triticum aestivum L.) yields in most major cereal growing areas of the world have been associated with shorter cultivars which incorporate the Rht1 or Rht2 height-reducing alleles. Considerable uncertainty still exists, however, concerning the growth of vegetative tissues, especially roots, of these shorter genotypes. The objective of this study was to determine how dry matter (DM) partitioning, in vegetative shoot and root tissues, is related to plant height as determined by the number of Rht alleles present (tall (no Rht alleles), semidwarf (Rht1 or Rht2), dwarf (Rht1 and Rht2) within a common genetic background. Tall, semidwarf, and dwarf near-isogenic lines were studied within each of four diverse genetic backgrounds. Six controlled-environment experiments were carried out in which plants were grown in sand (nutrients applied hydroponically) and harvested following anthesis. Stem and shoot (total aboveground tissue) DM plant-1 increased with plant 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 consistently related to plant height. In the absence of selection pressure, genotypes containing Rht alleles should have root DM comparable to their tall counterparts, and root/shoot ratios equal to, or greater than, their tall counterparts. The Rht alleles also decreased individual leaf blade areas, primarily through effects on leaf length, and increased stomatal frequencies of early leaves; effects on the flag and penultimate leaves were ambiguous, suggesting that the gibberellic acid (GA3) intensitive Rht alleles exert greater control during earlier growth stages.