Flower bud differentiation in alfalfa and response to water coercion

Plant flower bud differentiation is a prerequisite for seed production. Water is a crucial factor in maintaining normal physiological activities in plants, promoting flower bud differentiation, and ensuring seed development. In this study, the morphological differentiation characteristics of alfalfa flower buds and the effects of water stress on flower bud differentiation were evaluated in Medicago sativa L. XinMu No. 4. The paraffin section method was used to analyze the morphological attributes of bud differentiation, differentiation stages, and the bud development process in alfalfa under normal irrigation and water stress. The results showed that: (1) Based on the formation sequence of different primordia during flower bud development in alfalfa, the process of flower bud differentiation was divided into six stages according to the emerging order of each of the primordia of alfalfa: (i) nutritive growth stage, (ii) floret primordial differentiation stage, (iii) sepal primordial differentiation stage, (iv) petal primordial differentiation stage, (v) androgynophore primordial differentiation stage, and (vi) floral organ formation stage; (2) Compared with normal irrigation, moisture stress treatment decreased the transverse (1.69% to 26.84%) and longitudinal diameters (2.51% to 23.49%) of the flower buds (P < 0.05); (3) Water stress shortened the process of bud differentiation, causing bud differentiation to finish 4 days earlier, increasing the single order floret number.