1 Unravelling the effects of GA-responsive dwarfing gene Rht13 on yield and grain size

A set of near-isogenic lines (NILs) with dwarfing genotypes Rht-B1b, Rht13 and tall was grown in a phytotron glasshouse experiment to examine differences in biomass accumulation and partitioning. The objective was to determine how Rht13 backcross lines may have produced equivalent yields but lower levels of screenings (small grains) in multi-environment yield trials compared to sister lines carrying Rht-B1b or Rht-D1b. Compared to the tall, the Rht13 NIL grew at a similar rate until late stem elongation; both faster than the Rht-B1b NIL. From late stem elongation until anthesis, growth of the peduncle and penultimate internode were strongly reduced with Rht13 compared with both the Rht-B1b and particularly the tall NIL. In spite of the resulting large differences in length of the top two internodes, total water soluble carbohydrate contents were similar. Ear length was reduced in the Rht13 NIL compared to both the Rht-B1b and tall NILs suggesting a possible reduction in grain number that may contribute to the lower screenings observed in the field. Further results from the phytotron experiment and parallel field trials should determine if differences in biomass accumulation and partitioning are associated with reduced screenings and equivalent yield of lines carrying Rht13 cf Rht-B1b or Rht-D1b