Forced Flowering in Mandarin Trees under Phytotron Conditions

Experiments that involve citrus flowerings are usually limited to springtime. With these methodologies, researchers will be able to control and design when to obtain the flowers to work with. It is a clear and easy technique that allows to obtain flowers from young Mandarins at any time of the year.

Researchers can control dates and flower intensity. This technique can be used not only for Mandarin trees but also for other citrus trees as lemons or grapefruits and other fruit trees. To prepare, use a growth chamber measuring length of 1.85 meters, width of 1.85 meters, and height of 2.5 meters with a total volume of 8.56 cubic meters.

Check if regulations such as temperature for day and night, photo period, light intensity, and minimum relative humidity are available. Obtain the plant material from registered nurseries with a virus-free certification. For example, six Mandarin trees cultivars Clemenules and six Mandarin trees cultivars Nova.

Mandarin trees can be young, for example one or two-year-old varieties grafted onto root stocks. Use appropriate pots such as a plastic pot with diameter of 22 centimeters and height of 20 centimeters and prepare five liters of standard substrate based on 50%of high-quality white peat and 50%of coconut fiber. Irrigate the plants for the first time as soon as they arrive from the nursery to standardize moisture content.

Water by immersion. Cover the pots with water halfway for 20 minutes. Keep the plants outside in half shade without irrigation for three to five days.

Program the growth chamber for Mandarin trees based on the site's springtime conditions. Use two electronic controllers with dual output, one for day and one for night humidity. Use a timer to change from day to night.

To set up minium humidity, press and release the set button. When SP1 appears, press and release the set button and press the up key or down key to change the SP1 value to 50%For maximum humidity, press and release the set button and then press the up key or down key to change to SP2. Press and release the set button and press the up key or down key to change the SP2 value to 60%To set up the desired day temperature to 22 degrees Celsius, press and release the set button.

When SP1 appears, press the set button and then press the up key or down key to change the SP1 value. To set up the desired night temperature, offset set point one to access OS1 parameter. Press the set button for five seconds then press the down key three times.

When CnF appears, press the set button and then press the down button. When PA2 appears, press set two times with rE1 and OS1 appearing in sequence. Press set again and press up or down key to change the OS1 value to minus 11 degrees Celsius and then press the FNC button to exit.

After four weeks, increase the temperature by one degree Celsius and add a half hour of light. As the phytotron has variation ranges, the nighttime temperature may vary from 11 to 14 degrees Celsius and the daytime temperature from 19 to 22 degrees Celsius. Use two light kits with a reflector, an electric ballast sodium halide and high-pressure sodium 600 watt lamp to obtain the appropriate light intensity.

Use a lux meter to check illuminance. It is desired to be attained 55, 000 lux at the top of the crown and 40, 000 lux at the crown base. Before floral induction, place trees inside the phytotron and keep them for several weeks without watering them.

Distribute trees regularly so that each has the same available space and light. Distribute individuals and varieties randomly among positions. To use water stress for floral induction, after the first irrigation, do not irrigate trees until the water stress period is considered to have finished.

Look at leaf turgidity to check the water stress intensity everyday. When most leaves are flaccid but not have started to fall, consider enough water stress for floral induction. This usually happens after 22 days without watering.

Irrigate the trees abundantly after the water stress period. For this first irrigation, cover pots with water halfway to immerse for 20 minutes. Compare the total amount of leaves before and after the water stress period.

Calculate the percentage of fallen leaves which is an indirect measurement of the water stress suffered by each individual. At the beginning and the end of flowering periods, collect flowers once a day. On the days of maximum flower production, collect flowers twice a day and seven days a week.

Perform other management tasks such as to water trees approximately once a week after the water stress period and check the temperature and humidity settings with a data logger. In this experiment, three levels of water stress intensity were established for the same number of days without irrigation, low intensity which has five to 10%leaf fall of the Clemenules individuals, medium to high intensity which has 50 to 60%leaf fall of the Nova individuals, very high intensity which has 80 to 90%leaf fall of the Nova individuals. The vast majority of flowers were complete and viable.

Some small leafy flowers with very short petals were observed at the beginning of the flowering period probably due to the partial induction of some buds. The higher the leaf fall percentage the more water stress and therefore the greater floral induction intensity. Individuals with high induction displayed mainly leafless buds with one flower or several.

The individuals with intermediate induction showed mainly buds with a balanced number of leaves and flowers but also leafless buds with one flower or several and very few buds with many leaves and a few flowers. Individuals with low induction showed mainly buds with much more leaves than flowers. Water stress level can be estimated with leaf turgidity and will be correlated with floral intensity.

Dates, amount of flowers, and inflorescence type will be determined. This technique can be useful for any other fruit trees to obtain flowers at any time.