Floral buds differentiation and physiological changes in pseudobulb of Eulophia flava

Eulophia flava is a wild orchid with excellent ornamental and market value. The natural florescence misses the good sale season. It's necessary to acknowledge the characteristic of the floral bud differentiation to regulate the flowering period of E. flava. The paraffin section of developing floral bud was observed, and physiological changes were evaluated. The morphological process was divided into six stages: initial, inflorescence primordium, floral primordium, sepal primordium, petal primordium, and column and pollinia differentiation. In pseudobulbs, soluble sugars and protein content decreased at the early stage, then, increased. High carbon-nitrogen ratio was favourable to the commencement of floral bud differentiation, and high level of total nucleic acid was benefit for the initiation. Relatively lower endogenous IAA and ABA concentration was helpful for the morphological formation of floral bud. GA 3 inhibited the differentiation at the early stage, and promoted it later. In the whole process, ZR content increased gradually.