Abstract: In order to clarify the regulating mechanism of rice spikelet development， a spikelet\|rudimentary rice mutant （spd\|hp73） was obtained from the offspring of hp73 mutated by60Co γ radiation. Genetic analysis and gene mapping indicated that the phenotype was controlled by a single recessive gene， named as spd\|hp73， and the spd\|hp73 locus was mapped to the long arm of chromosome 4 between SSR marker RM471 and RM273. In the present study， we observed the spike development dynamic of both wild type （WT） and mutant by stereomicroscope and scanning electron microscope. The results showed that: there was no significant difference in the morphology of spikelet between mutant and hp73 in the early stage. But the morphology of inflorescence changed during the pistil and stamen formation. In this stage， the spikelet number of mutant was significantly reduced， and almost all the spikelets on primary branch and secondary branch were degradated. This result indicated that the main function of spd\|hp73 gene was possibly to control spikelet number during the spikelet （or floret） primordium differentiation.

Key words: rice, spikelet\, rudimentary mutant, spike differentiation, scanning electron microscope （SEM）, stereomicroscope