FLORET DEVELOPMENT IN NEAR-ISOGENIC WHEAT LINES DIFFERING IN PLANT HEIGHT

The effects of Rht1 and Rht2 alleles on the dynamics of floret develop ment in isogenic lines (dwarf, DD; semi-dwarf, SD and standard height, SH) of spring wheat were investigated. Studies were conducted on whea t grown in the held in each of 4 years and where water and nutrients w ere non-limiting. The number of grains per spike was significantly gre ater in the Lines with Rht alleles than in the SH lines. Grain number for each line was such that DD>SD>SH. Grains per spike varied with the number of grains per spikelet rather than number of spikelets per spi ke. Grains per spikelet in turn varied with the number of fertile flor ets at anthesis. Florets were considered fertile when male and female reproductive organs had developed green anthers and bifidum stigma, re spectively. The dwarfing genes had no effect on the percentage of fert ile florets setting grain. Increased number of fertile florets per spi kelet due to the presence of Rht1 and Rht2 alleles in the genome was a consequence of the higher number of relatively distal primordia, to p rogress to the stage of fertile floret at anthesis in the DD and SD th an in the SH lines. This ability to allow that a greater proportion of distal florets maintain a normal rate of development was related to t he fact that Rht alleles produced a more favourable assimilate partiti oning to the spike during the pre-anthesis period associated with the reduction in stem growth imposed by Rht alleles. This allowed a higher proportion of the later-initiated floret primordia to produce fertile florets at anthesis. (C) 1998 Elsevier Science B.V. All rights reserv ed.