Gibberellic acid-sensitive dwarfing genes reduce plant height to increase kernel number and grain yield of wheat

The Norin-10 dwarfing genes, Rht-B1b (Rht1) and Rht-D1b (Rht2), have been u sed to reduce plant height and increase grain yield in wheat breeding progr ams worldwide. Other dwarfing genes are available to reduce plant height of wheat but little is known of their effects on grain yield. A set of random , F-5-derived wheat lines containing either minor genes for reduced plant h eight, or major gibberellic acid (GA) sensitive Rht8 and Rht9 dwarfing gene s, were obtained from 3 different populations. Environment mean yields rang ed from 2.5 to 4.6 t/ha. Genotypic variation was large and significant (P < 0.05) for plant height, grain yield and its components, and kernel number and size. Approximately 30% of lines were as short as variety Hartog, while kernel number per m(2), harvest index, and grain yield of the shortest GA- sensitive lines were not significantly different (P < 0.05) from the commer cial semidwarf checks Janz or Hartog. Furthermore, genotypic differences in plant height were genetically correlated (r(g)) with variation in kernel n umber (r(g) = -0.76*), harvest index (-0.71*), and grain yield (-0.62*). Th ese correlated effects were confirmed with retrospective selection for heig ht and were consistent with reported height effects of Rht-B1b and Rht-D1b dwarfing genes on kernel number and harvest index in wheat. Plant height di fferences among GA-sensitive lines were independent of variation in seedlin g characteristics (r(2) = 0.01-0.02 n.s.), while a number of reduced-height lines produced 50% longer coleoptiles and greater seedling biomass than Ja nz. These studies demonstrate a correlation between the shorter height of G A-sensitive dwarfing genes and increased grain yield, and suggest their pot ential for improving wheat establishment through greater coleoptile length and early vigour.