Forced Flowering in Mandarin Trees under Phytotron Conditions

Phytotron has been widely used to assess the effect of numerous parameters on the development of many species. However, less information is available on how to achieve fast profuse flowering in young fruit trees with this plant growth chamber. This study aimed to outline the design and performance of a fast clear methodology to force flowering in young mandarin trees (cv. Nova and cv. Clemenules) and to analyze the influence of induction intensity on inflorescence type. The combination of a short water stress period with simulated spring conditions (day 13 h, 22 degrees C, night 11 h, 12 degrees C) in the phytotron allowed flowers to be obtained only after 68-72 days from the time the experiment began. Low-temperature requirements were adequately replaced with water stress. Floral response was proportional to water stress (measured as the number of fallen leaves): the greater the induction, the larger the quantity of flowers. Floral induction intensity also influenced inflorescence type and dates for flowering. Details on artificial lighting (lumens), photoperiod, temperatures, plant size and age, induction strategy and days for each stage are provided. Obtaining flowers from fruit trees at any time, and also several times a year, can have many advantages for researchers. With the methodology proposed herein, three, or even four, flowering periods can be forced each year, and researchers should be able to decide when, and they will know, the duration of the entire process. The methodology can be useful for: flower production and in vitro pollen germination assays; experiments with pests that affect early fruit development stages; studies on fruit physiological alterations. All this can help plant breeders to shorten times to obtain male and female gametes to perform forced-crosses.