Spiking and Flowering of the Phalaenopsis. Part I. Spiking technique

Transcription

1 Spiking and Flowering of the Phalaenopsis Part I. Spiking technique The spiking and flowering technique are the key techniques for the Phalaenopsis industry. The flowering time is so important for obtaining the high benefit, that is, the blossoms of orchids need to be sold on time. So the quality and timing of flowers are the basic requirements for orchids growers. What is the basic principle of spiking? Orchids are induced from the vegetative to reproductive phase. There are two conditions for the Phalaenopsis: 1.the plant has reached the mature stage, 2.the plant is treated with physiological stress. The above conditions are only the rules, not the law. The numeric values of the rules vary by varieties. For example, cooling temperature is an important factor for spiking. The required cooling day temperature is 25 for amabilis and 20 for P. Fortune Saltzman. The mature stage also differs by varieties. Some varieties could be induced to spike at the culture period of 6 or 8 months after deflasking. Some varieties required 14 months to reach maturity. The adequate programming of Phalaenopsis from mature plants to flowering is in Table 1. The spiking technique is introduced as follows. The basic factor affecting the spiking of Phalaenopsis is the genetic characteristics. Environmental control and management are other key points for the spiking technique. A. Environmental stress The important environmental factors for orchids culture include the day and night temperature, relative humidity, light intensity and light period. The proper humidity level ranges from 50% to 80% RH. If the humidity is too low (< 50% RH) or too high (> 90%) and without ventilation, the humidity could have a significant effect on the plants. In most cases, the humidity in the greenhouse could be controlled within the adequate range. 1

2 Environmental stresses are controlled by the temperature and light setting. 1. Temperature The cooling temperature has a significant effect on the spiking. However, the set of day and night temperature are affected by the variety s characteristics. The spiking percentage is a function of the accumulated cooling temperature. The larger the difference between the growing and cooling temperature, the shorter the spiking period, that is, low day and night temperature could enhance spiking. However, the endurance of the low temperature needs to be considered. Some varieties are sensitive to low temperatures. If the cooling temperature is too low for the variety, these plants are easily damaged by the cooling treatment. Some varieties grow well at high day and night temperatures and it induce two spikes easily by lower day and night temperature (e.g., 18 ). Some varieties, such as amabilis, are cultured at high day temperature (27-30 ) and medium night temperature (20-23 ). These varieties could be induced to spike by cooling the day temperature. The environmental factors of different stages for several Phalaenopsis varieties are in Table Light intensity and period In the cooling stage, the temperature is kept low, so the photosynthesis rate is decreased. These plants need to have more light intensity to compensate for the temperature factors and to accumulate enough dry matters, especially carbon source. The recommend light intensity is in Table 2. The optimal light period is 14 hr. The light period could be maintained in the range of 12 to 16 hr. If the natural day light period is less than 12 hr, artificial light needs to be supplied to extend the light period. B. Management The management includes watering, fertilizing, and hormones application. The 2

3 relationship between spiking and fertilizing could be explained by the principle of plant physiology. The increase in ratio of C/N of the plant could help the change from the vegetable to reproduction stage. Two ways can be used to increase carbon sources: increase temperature and light intensity. The N source could be reduced by decreasing the N source and increasing other fertilizer components. The spiking pretreatment could be executed one month before the setting the temperature for cooling. The useful technique is to increase the temperature and light intensity in the greenhouse, decrease the N concentration and increase the P and other components. It worth mentioning that the fertilizer ratio should not be changed abruptly. The spiking period ranges from four to eight weeks. The fertilizer formula could be applied in the order of (N-P-K) and (N-P-K) interchangeably. The application of hormones is not ideal. The concentration of hormones is not easy to control. If the concentration is too high, the shape of flower could be changed unpredictably. Using hormones only has a small effect on the spiking. However, the application of hormones with the cooling stress could increase the spiking percentage and shorten the cooling period. An adequate hormone levels are influenced by the characteristics of varieties. C. Abnormal physiological stress Some abnormal physiological stresses could induce spiking. However, with abnormal stress, plants may be damaged and the flower quality poor. Abnormal stress includes as following: 1. No water supply or insufficient water quantity. 2. Root damage: the roots are injured during transplanted or transported. 3. The abrupt change of temperature, expressed as the rate of change of air temperature to time. If the temperature change rate is higher than a criteria value, the temperature stress could induce stress and result in spiking. Two common conditions are found in subtopic regions for this abnormal stress. 3

4 1. Forced ventilation in winter In winter, the greenhouse temperature is always maintained at higher level for the growing requirement of Phalaenopsis. The outside air temperature is low because of the cold current or at night time. Mechanical ventilation is operated at a fixed interval period. If the cold air is sucked into the greenhouse suddenly, the temperature change rate is high and can easily induce spiking. 2. Air temperature decreases rapidly in summer Rain storm is a common condition in summer. The air temperature decreases rapidly and the cooler air is inhaled into the greenhouse by the exhaust fans. The temperature change rate induces spiking. As the outside temperature returns to the warm state, the high air temperature is inhaled into the greenhouse and cooler air is exist. The change pattern of air temperature induces spiking and can easily damage plants. In the literature of Anthurinfo, they mentioned that the influence of the temperature for blooming is about 60%, light 30% and other factors 10%. This ratio may differ for setting the values for the greenhouse environment, different management techniques and various varieties. From the above discussion, several factors could be combined to induce spiking. The optimal technique controlled by growers is to create a stressful environment but avoid damaging plants. 4

5 Table 1. Programming of Phalaenopsis from mature plants to flowering Operation stages Physiological reaction 1. Environment : Optimal conditions 2. Fertilizing, Formula A (N-P-K) Ⅰ. Growing stage 1. Mature plants 2. Sufficient dry materials accumulation 3. Healthy roots 1. Increase day temperature, Increase light intensity 2. Increase P, reduce N, Ⅱ. Pretreatment stage 1. Increased dry matter accumulated at the leaves and stems Formula B (N-P-K) 1. Decreasing temperature, Increasing light level Ⅲ. Spiking 1. Changes in endogenous levels of plant hormones 2. Interchangeability of Formula A and B 3. No hormones application 4. Abnormal stress also enhance Spiking 1. Increase temperature, light level is normal or a little higher than normal level 2. Fertilizing, Formula A (N-P-K) Ⅳ. Spike extending 1.The carbon is produced by photosynthesis at leaves 2. The carbon source is transported from leaves to spikes 1. Reduce temperature, light level is At normal level 2. Fertilizing, Formula A Ⅴ. Flowering 1. The carbon is produced by photosynthesis at leaves and then transported to spikes, buds and flowers. 2. UV-B is required to enhance the bright color of flowers. 5

6 Table 2. Environmental factors of different stages for several Phalaenopsis varieties Data sources: Big white Small white Culture Guide V3 Hsin-Yen Fortune Queen of Floricultura b.v. amabilis Beauty Saltzman Beer I. Growing 1.T dg Stage 2.T ng lux lux Ⅱ. 1.T dp Pretreatment 2.T np lux lux lux lux Ⅲ. Spiking 1.T dc T nc lux lux lux Ⅳ. Spike 1.T de extending 2.T ne lux lux Ⅴ. 1.T db Blossoming 2.T nb lux lux Note: 1. Growing temperature at day and night, T dg, T ng. 2. Pretreatment temperature at day and night, T dp, T np. 3. Cooling temperature at day and night, T dc, T nc. 4. Spike extension temperature at day and night, T de, T ne. 5. Blossoming temperature at day and night, T db, T nb. 6

7 About the author: Professor Chiachung Chen, Ph. D. Biosystems Engineering Laboratory National ChungHsing University 250 KuoKuang Rd., Taichung, Taiwan Tel: , Fax: Web site: bse.nchu.edu.tw 7