Florogenesis of the Mediterranean geophyte Narcissus tazetta and temperature requirements for flower initiation and differentiation

Plant florogenesis is determined by the interaction between the genetics of the individual plant and environmental factors. Flower initiation and development of many studied plant species require low temperatures. However, some geophytes form flowers within the bulb during the summer quiescence period and do not require low temperatures for florogenesis. Narcissus tazetta was employed to study, in detail, the stages of flower development during the summer period, with special emphasis on the effect of temperature on inflorescence initiation. The sequence of morphological processes occurring during floral initiation and development was observed by SEM. During 3 years, the bulbs were subjected to different storage temperatures during the summer, and records were taken of the percentage of apical meristems that shifted from vegetative to reproductive development. Flowering and inflorescence quality were recorded after planting. It was concluded that, under natural conditions, the temperature increase in June, during the growth of the mother plant, leads to the transition of the apical meristem to the reproductive stage. Floral initiation and reproductive development in N. tazetta is promoted by high temperatures with an optimum of 25 °C. Sub- and supra-optimal temperatures (20 and 30 °C) delayed differentiation, while lower temperatures (12 °C) inhibited florogenesis completely.