Presence of these semi-dwarfing genes results in gibberellic acid
insensitivity causing reduced internode elongation, and therefore
shorter final plant height than parental lines without the semidwarfing gene. Within the general classes of semi-dwarf (based
upon gibberellic acid insensitivities and the presence of Rht-B1b
or Rht-D1b genes) and conventional height wheat (syn. tall wheat;
gibberellic acid sensitive and the presence of Rht-B1a and Rht-D1a
or the absence ofRht-B1b and Rht-D1b genes), there is considerable
variationinplantheight.Thedifferencesinplantheightinthesemidwarfandtallwheatclassesarepresumablyduetounknownminor
genes that also affect plant height. The presence of these minor
genes explains the range in plant height within major gene groups,
e.g., those found in the studies of Flintham et al. [15]. The presence
of these minor genes was obvious in that the tall controls ranged
in height from 99.4 to 141.4cm and the Rht-B1b near-isogenic
genotypes ranged in height from 84.0 to 124.3cm. However, the
ratios of the semi-dwarf and dwarf genotypes to the tall genotypes
were very similar for all of the isolines. In this study, a range of
plant heights were observed within the semi-dwarf and tall wheat
classes,whichwasassumedduetounknown,minorgenesaffecting
plant height