Forced Flowering in Mandarin Trees under Phytotron Conditions

Summary

Here, we present a protocol to force flowering in mandarin trees under phytotron conditions. Water stress, high illuminance and a simulated spring photoperiod allowed viable flowers to be obtained in a short period of time. This methodology allows researchers to have several flowering periods in 1 year.

Abstract

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 °C, night 11 h, 12 °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.

Introduction

Phytotron has been widely used to assess the effect of numerous parameters on the development of many herbaceous and bulb plants. Species such as rice¹, lily², strawberry³ and many others⁴ have been evaluated under phytotron conditions. Chamber experiments on forest trees have also been carried out to evaluate ozone sensitivity on juvenile beech^5,6, and to assess the influence of temperatures on frost hardening in seedlings of Scots pine and Norway spruce⁷. Less information is available about....

Protocol

1. Growth chamber characteristics and regulation requirements

1. Use a growth chamber measuring 1.85 m x 1.85 m x 2.5 m (L x W x H) with a total volume of 8.56 m³ (Figure 1). A bigger or smaller growth chamber can be resorted to if necessary.
   NOTE: Almost any room, or even a greenhouse, can be adapted to be used as a growth chamber.
2. Check if regulations such as temperature (day/night), photoperiod (day/night), light intensity and minimum relative humidity are available (Figure 2).
   NOTE: Timers should allow temperature and light switch (on/off) control at least every....

Results

The experiment was carried out in the plant growth chamber located at the Valencia Polytechnic University's Gandía Campus (municipality of Gandía) in the province of Valencia, Spain (39° 28′ 53.95″ N, 0° 20′ 37.71″ W), in autumn and winter (2017 Oct. 26 - 2018 Feb. 5) (Table 1). Six mandarin trees cv. 'Clemenules' (a bud mutation of Citrus clementina hort. ex Tanaka) and six mandarin trees cv. 'Nova'.......

Discussion

It was possible to force the flowering of young citrus trees (only 2 years old) quickly and at any time with profuse flower production (around 216 flowers per tree). In previous studies^14,15, flower initiation was induced by low temperatures and the process lasted around 120 days. The combination of a short water stress period with spring conditions in the phytotron allowed this time to be significantly reduced, with mandarin trees (cv. Nova) flourishing after 68.......

Materials

Name	Company	Catalog Number	Comments
Data-logger	Testo	Testo 177-H1	Testo 177-H1, humidity/temperature logger, 4 channels, with internal sensors and additional external temp
Data-logger sotfwae	Testo	Software Comsoft Basic Testo 5	Basic software for the programming and reading of the data loggers Testo
Electronic controller differential	Eliwell	IC 915 (LX)  (cod. 9IS23071)	Electronic controller with 2 set points and differential set point adjustment
Electronic controller dual	Eliwell	IC 915 NTC-PTC	Electronic controllers with dual output
Growth chamber - phytotron	Rochina		Chamber measuring 1.85 x 1.85 x 2.5 m (L x W x H) with a total volume of 8.56 m3. With temperature (day/night), photoperiod (day/night), light intensity and minimum relative humidity control.
Light kit	Cosmos Grow/Bloom Light		Light kit with reflector, electric ballast sodium/halide and high-pressure sodium (HPS) 600W lamp
Luxmeter	Delta OHM	HD 9221	HD 9221 Luxmeter to measure the light intensity
Plant material	Beniplant S.L (AVASA)		Mandarin trees from registered nurseries with a virus-free certification
Substrate	Plant Vibel		Standard substrate based on quality 50% white peat and 50% coconut fiber