Thailand is one of the tropical countries that can grow dragon fruit being both an exporter and importer of the fruit depending on months of the year. Most dragon fruit production in Thailand can be harvested from natural season production (April to October). However, for the off-season (November to March), there is less amount of fruit that can be produced and imported. The main production areas are in Thailand’s central plains and the uplands of the northeast. The problems of the on-seasonal production are fruit oversupply in June-July whereas the limited off-season production can be produced only in irrigated areas. Induction of the off-season flowering by means of additional light is effective but are limited by a relatively high energy cost. Off-season flower induction using CPPU can be done at a lower cost and faster. However, the limitation of this method requires grower’s skills to find the proper buds to induce flowering. Most produce are sold and consumed in the country. Some qualified for export standards can be exported overseas. Post-harvest technology research can prolong the dragon fruit for long-distance export but are not commercially implemented. In general, the Thai dragon fruit production is predicted to increase with the use of appropriate technology and methods to control the chemical residue to meet the export standards.
Keywords: Pitaya, forchlorfenuron, CPPU, off-season
Dragon fruit plant can easily grow in almost all types of soils, so it can be grown in wide areas of Thailand. However, the main planting areas are located in the lowlands of the Central Plains around Bangkok and highlands of Phu Ruea District, Loei Province, which has a slightly different planting system due to its geography. In the central lowlands, the land is flat due to the delta deposits with a high groundwater. Planting beds in the orchards in this area needs to be raised as furrow and ditch (Figure 1). This makes the furrow aims to increase the soil layer for root systems above groundwater. The orchards are surrounded with soil barrier to prevent flooding during the rainy season. Therefore, this orchard can access water supply almost all-year round, even in the dry season. Moreover, this is also suitable to produce off-season dragon fruit.
For planting in upland areas in the upper northeast, the dragon fruit is planted on a flat land, which the farmers can work more conveniently than planting in the ditch system (Figure 2). However, this cultivation relies only on seasonal rain. There is mostly no irrigation system so the fruit quality was relatively poor and unable to produce off-season due to water shortage.
Thailand is geographically located slightly above the equator so the plants flower naturally from March to September. The fruits can be harvested from April to October with approximately 1-2 harvests per month. The fruit price in the beginning of the season (Mar-Apr) is much higher than those in thr mid-season (around June-July). This abundant fruit causes a serious problem to the growers due to its very low price. It might be proper for further food processing. Whereas, during November and March, there is less amount of fruits since it is off-season and the fruit price is expensive. Therefore, if farmers can produce off-seasonal fruits, it will be an alternative way to solve this problem.
DRAGON FRUIT PLANTING
Owing to a creeping plant, the plant grows as with increased stem length vertically along the cement pole. This issimilar to the growth of some plants in other Southeast Asia countries. The distance between the poles is about 3 to 3.5 meters. The pole height above the ground is about 1.5 meters while about 0.5 meter underground. This pole can be either a 2-3” concrete pole or 4-6” hollow sewage cement pipe depending on availability. A small scaffold made from cement or iron bars wrapped with old bicycle tire is installed on the pole top to support the dragon fruit stem weight.
Three to four stem cuttings, as a propagule, are planted vertically nearby the pole base tied up to the pole. The plant will later grow up to the top.
The planting materials popularly are obtained from stem cuttings derived from cutting old stems at the end of the production season to control canopy (Fig 3). The stems can be cut into about 20-30 cm long before planting in a 2”x6” plastic bag filled with media of coconut coir, carbonized rice husk and manure. Dipping the stem base with rooting hormone as IBA is recommended to get rooting quickly. The cutting can be rooted within 1 month and grow further for 8 to 10 months to get the first flowering. The fruit yield increase gradually to get an optimum from the 2nd year on.
For soil management, dragon fruit plant does not prefer damping soil and can tolerate drought well. However, to get both quantity and quality of the produce, sufficient water is required especially during the development of flowers and fruits. Drought condition in this period results in flowers or fruits to fall easily but waterlog causes root rot. Therefore, the management of the planting beds needs to be well drained especially during rainy season and relied on soil type. Sandy loam is preferred due to proper water holding and aeration. The appropriate soil pH is 6.3 - 6.8.
WATER RESOURCE AND WATERING
Even though dragon fruit is xerophytes, to get good quality products, sufficient water is required. Dragon fruit plantations in which are located in the upland area (Loei Province) rely solely on rain water which will be around April, and will intermittently continue until October. Most produce are obtained from natural flowering. During November to March as a dry period, the fruits cannot be produced off-seasonally. Few orchards apply drip irrigation to get better quality fruit. On the other hand, the orchards in the central plains can access water resource surrounding them consistently, even during November to March. Therefore this area should be able to produce off-season fruits with proper technology and at reasonable cost.
Although water shortage is not an obstacle for production in the lowland areas, watering the plant is still necessary. The plant roots spread out on the soil surface and it might dry up easily and affect the fruit’s growth and fruit production. The growers mostly water the plants 1-2 times a week depending on the environment such as soil moisture, rainfall, temperature etc. A popular watering manner is sprinklering with water pump installed on a small boat dragged along the ditch.
Like other crops,dragon fruit plants need fertilizers. In Thailand, there is still no research recommendation for fertilizer application. Most farmers apply fertilizer according to their experiences or those of other farmers. Both organic and chemical fertilizers are commonly used in Thailand depending on the management and accessibility of individual farms.
Dragon fruit orchards in the uplands usually apply mainly with organic fertilizers as manure from chickens or cow dung 1-3 times a year, about 15-20 kg per time per pole at before and after the production season. In addition chemical fertilizers, with even N-P-K formula are also applied one to two times a year alternating with high potassium. However, well-managed orchards having irrigation systems apply more fertilizers than mentioned. For example, manure two to four times a year and the little chemical fertilizer for every two weeks, increase efficiency of fertilizer and reduce element loss.
There are also some organic dragon fruit orchards, which focus on using only manure. This fruit is sold at a much higher price than usual. However, the fruit size is usually smaller than the fruit applied with organic and chemical fertilizers.
Dragon fruit plant is a long day plant that requires continuous light during the daytime, not less than 12 hours (or continuous darkness less than 12 hours), so it can bloom. Geographically Thailand which is located in the tropics above the equator, is considered a good place to grow dragon fruit which bloom naturally from March to September and can be harvested from April to October more than seven times a year. During June to July, the most productive period, large numbers of dragon fruits are ready to be harvested over market demand causing a very low fruit price while from October onwards, there is no seasonal dragon fruit products, resulting in high prices. Off-season production is therefore very important to help farmers earn income from high-priced fruits. Off-season induction can be done physically, including additional lighting and use of chemical plant growth regulators.
However, the key factor for off-season production is the availability of water during flowering and fruit development. If there is lack of water, the flowers dry up and fall easily. Therefore, in rain-growing areas, it is not suitable for off-season production. Only the orchards that can provide sufficient water during the off-season are proper for producing off-season dragon fruit.
Supplemental lighting during the night on dragon fruit plant can be simulated to long day conditions or night-break. This method can be easily done by connecting the power cord and installing a lamp of 100-watt incandescent bulb above the canopy along with the planting rowsThe lights are turned on to increase as specified period. Turning on light 10 hr/day for 18 days can induce flower bud development during November to December. The shorter period of light as 3 hrs/ day, the more number of days required, probably up to 30 days. However, the number of flowers might be less than the first manner. Therefore, light intensity, light quality, light period and number of lighting days are necessary factors in off-season flower induction. However, this method is not well adopted in Thailand due to high electricity cost. Lighting on unhealthy plants results in less flowering of buds or sometimes buds unable to flower. Photosynthate stored in the stems is a key for off-season fruit production. In addition, choosing energy-saving lamps (LED) or light with specific wavelengths is an alternative to significantly reduce the costs.
Plant growth regulators
In addition to additional lighting, in some areas shortage of electricity or high electricity costs, chemical methods may also be applied by using forchlorfenuron or CPPU, a synthesized cytokinin. The flower buds induced are satisfied in both white and red pulp cultivars. Begin with choosing the perfect mature stems with age over five months old normally curved and hung down to the ground, the spines cover a swollen bud facing out of the canopy are sought for. The spines are gently scratched out, and then brush the white bud with CPPU solution. The buds develop into a small flower within four to seven days and continue to grow up afterward (Figure 4). This takes a shorter time compared to additional lighting.
Lack of water during this period causes the young flowers to wilt and fall down. The limitation of this method is finding the proper buds under the spines. Some buds are determined to be vegetative buds, so new vegetative shoots emerge instead of new flowers (Figure 5). Therefore a skill to choose proper buds is required. From experiments, it was found that the induction of off-season flowering during November (ending of natural flowering season) is more successful than during February (early of natural flowering season). Environmental factors such as temperature and humidity are possibly involved.
As mentioned above, plant health and food stored in the stems are crucial. The stems previously bearing fruits may have less food stored and not enough healthy. Therefore seasonal flowers on that stems should be removed as early as possible before off-season flower induction. This allows the stems to accumulate photosynthate during peak of fruiting and ready for flower induction.
The peel color of dragon fruits that is ready to harvest turns from green to red, dark red or purple red with bright green bract. The fruit age is approximately 35-40 days after flowering is most suitable for harvest. When fruits are harvested early, the taste is too sour. On the other hand, if they are harvested late, they are overripe and translucent. The fruit should be harvested in the morning to avoid heat and cut by curved trimmer at the base of the stem end then collected with care to prevent bruising for grading and packing.
There are few orchards that provide qualified dragon fruit to be sold to the European export standard even post-harvest technology is available. The recommendations include cool storage at 8-10C prolonging the fruit up to three weeks instead of a week at room temperature. Pre-cooling the fruit right after harvest is a known practice and is done by immersing in 4C water with ice to reduce field heat. Chlorine should be added to control the pathogen in the cool water. Heat treatment by dipping the dragon fruit in 50C water for 3-5 minutes can delay bract yellowing. Modified atmosphere with reduced oxygen and increased carbon dioxide and keep the bract fresh. These are optional manners for some farms being able to export dragon fruits.
Anonymous. 2019. Postharvest technology for dragon fruit. (http://www.siamedunews.com/index.php?mo=3&art=42301291; Accessed 8 August 2019) (in Thai)
Junthasri, R., 2009. Dragon Fruit. OdianStore, Bangkok. (in Thai)
Saradhuldhat, P., T. Boonklam and T. Havananda, 2016. Off-season floral induction in white and red flesh dragon fruit by forchlorfenuron. Songklanakarin Journal of Plant Science 3 Suppl.(1): M04/49-53. (in Thai)
|Date submitted: September 10, 2019
Reviewed, edited and uploaded: October 18, 2019