Evaluation of Low Cost Protected Structure for Commercial Cultivation of Dendrobium Cv. Sonia under Assam Condition

Dendrobiums are most popular tropical orchid getting fame as cut flowers in India as well as in the world. The total orchid cut flower trade of the world mostly consists of 70-80 per cent Dendrobium species (Cheamuangphan and Panmanee, 2013). About 103 species of Dendrobium orchids are reported from India (Singh et al., 2001). Dendrobium cv. Sonia flowered throughout the year with peak flowering during August to October and March to June under North east region. Dendrobium grows best at night temperatures between 15-18°C and day temperatures 23-29°C. They can grow both in tropical and subtropical climate with warm bright light (25,000-30,000 lux), 60-80 per cent of relative humidity and good ventilation. Therefore, Dendrobiums are grown under different protected condition for both plant sale and cut flowers production. But, in North East India, Dendrobium orchids are normally grown under iron frame shade net houses which are quite vulnerable to cold injury during extreme winter period and heavy rain during monsoon period which causes severe impediment in growth and flowering. Further, the existing iron frame structures setup at different parts of the state for growing Dendrobium orchids are very costly in nature which is not affordable by small and marginal farmers and also the existing structure do not have provision for proper utilization of the vertical space. Keeping in view the export potential of orchids and the requirement of small farmers as well as the abundance of bamboo in the North Eastern Region, it is necessary to evaluate a suitable low cost orchid growing structure which is capable of providing optimal growing condition for the crop. It gives an added advantage to both small and marginal farmers, who wish to take up orchid industry for more profit.
 

The present investigation entitled “Evaluation of low cost protected structure for commercial cultivation of Dendrobium cv. Sonia under Assam condition” was conducted in the Experimental Farm, Department of Horticulture, Assam Agricultural University, Jorhat during the period of 2018-2019 for two seasons. The experiment was laid out in factorial completely randomized design with 10 treatment combinations replicated five times. The first factor comprised G₁ (Bamboo frame structure covered with fixed 200 micron UV film with top ventilated and 50% agro shade net as ceiling), G₂ (Bamboo frame structure with fixed 50% agro shade net as cladding material), G₃ (Bamboo frame structure covered with fixed 200 micron UV film with side removable and 50% agro shade net as ceiling), G₄( Bamboo frame structure with fixed 50% agro shade net and 200 micron UV film as top covering), G₅ (Bamboo frame structure with 200 micron UV film side removable and fixed 50% agro shade net as covering). The second factor comprised T₁-1 tier (40 cm above the ground level), T₂-2 tiers (40 and 100 cm above the ground level). Dendrobium cv. Sonia was raised in 5 low cost growing structures oriented in North-South direction with a size of 4 m length, 4 m width and central height of 3 m. The frame of the house was constructed with bamboo and was covered with 200 micron UV stabilized polythene and Agro Shade net (50 per cent) of green colour. Plantlets were planted in the plastic basket of size 6" depth and 4" diameter and placed on raised platforms (Bench system). The basket was filled laying 1" at the top with a mixture of charcoal, coco husk and coco peat. Potted plants were arranged at the rate of 20 plants on bamboo bench at a size of 1m breath and 3 m length. Fertilizer mixture NPK- 19:19:19 @ 2g/L was given twice a week as foliar spray. The mineral nutrient treatments - Tracel 20 EC @ 2g/L was applied as foliar spray at 15 days interval.
       
The data were collected on various parameters during vegetative and flowering period from four randomly tagged plants in each replication. All the observations were recorded for two growing season i.e. 2018 and 2019 and then pooled over years analysis was done using Fisher’s method of analysis of variance in CRD as described by Panse and Sukhatme (1978).
 

Growth characters
 
The data (Table 1 and 2) indicated that the different protected structures and tiers had significant effect on growth characters. Amongst the protected structures, G₁ was the best for increasing the growth characters viz., plant height (45.26 cm), leaves per plant (11.65), leaf area per plant (569.61 cm²) and height of pseudobulb (25.67 cm). Similarly, T₂ was found to be superior in respect of the growth characters viz., plant height (42.57 cm), leaves per plant (10.54), leaf area per plant (532.47 cm²) and height of pseudobulb (24.13 cm). Good vegetative growth indicates better accumulation of photosynthates in plants. Faster growth is essential especially during juvenile stage for better flowering later on. In the present study, G₁ (Bamboo frame structure covered with fixed 200 micron UV film with top ventilated and 50% agro shade net as ceiling) was found to be superior amongst the growing structures. This phenomenon could be attributed to the favorable environmental conditions viz., optimum temperature, relative humidity, light intensity and proper air circulation inside the growing system which may drastically influence the growth of the plants. Because, natural ventilation affects both the air temperature and humidity which directly affect crop transpiration and carbon di oxide concentration that affects the photosynthesis process of crop (Hanan 1998). Again, 50% shading and better air circulation in G₁ which has a positive effect on plant physiology by preventing a down regulation of photosynthesis during periods of high radiation. These findings are in confirmatory with the findings of Naik and Kumar (2015) who reported that top ventilated poly house had the maximum influence on plant height (25.50 cm). Similar observations of increasing the leaf area due to better light and shading were made by Pires et al. (2012) in an experiment on epiphytic orchid Miltonia spectabilis var. Moreliana. Zou and Liu (2010) observed that during the pseudo bulb thickening phase, the Dendrobium nobile should be grown in full sun with good air circulation to produce strong pseudobulbs.




 
Flower characters
 
The data pooled over years of flower characters were tabulated in (Table 3, 4, 5 and 6). The different protected structures and tiers had significant effect on the flower characters of Dendrobium cv. Sonia. Amongst the growing structures G1 exhibited minimum days for bud visibility to opening of first floret (19.00 days), days for opening of first floret to full bloom (15.80 days) as well as the highest value for spikes per plant (4.40), spike length (38.17 cm), florets per spike (9.50), floret diameter (9.28 cm), self life of spike (44.60 days) and vase life of spike (30.35 days). Between the tiers, T₂ took minimum days for bud visibility to opening of first floret (21.82 days), days for opening of first floret to full bloom (18.99 days) as well as the highest value for florets per spike (7.60). Results revealed that minimum duration for first floret open and full bloom were recorded in G₁ compared to others. This treatment resulted earliness in flowering which recorded 8 days reduction to first floret open compared to the G₂. This might be due to the fact that to utilization of shade nets as a ceiling corroborating with ventilation on G₁ may be create a favorable temperature range both in dry and wet conditions during flowering time of Dendrobium cv. Sonia. G₁ might have increased number of flowers had positive and significant correlation with shoots and pseudobulbs production. Thus, the increased number of leaves, leaf area on plant growth helped in better way to synthesis of carbohydrates and their utilization to give up extra growth, thereby increasing the production of spikes as compare to others. Moreover, this might be due to favorable microclimate helps in accumulating more amount of assimilates which are needed for improvement of spike. Similar trend of report was made by Sugapriya et al., (2012).









Plants were placed on T₂ (40 cm and 100 cm above the ground) showed superior performance for most of the flower and growth characters compared to T₁. The possible reason for the reduction of temperature with increase in height of the greenhouse is due to the fact that the inside temperature will decrease with increase of ventilation rate.
 

It can be concluded from the above study that G₁ (Bamboo frame structure covered with fixed 200 micron UV film with top ventilated and 50% agro shade net as ceiling) and G₄ (Bamboo frame structure with fixed 50% agro shade net and 200 micron UV film as top covering) are comparatively suitable for healthy growth and flowering of Dendrobium cv. Sonia under Assam condition due to utilization of 200 micron UV film causes privations of damage from cold and heavy rain. Moreover, combinations of shade net and top ventilation were maintained the optimum temperature and relative humidity during the winter months (January to February) as well as during the summer months (March to May). Similarly, T₂ (2 tiers-40 and 100 cm above the ground level) showing better performance as compared to T₁ for proper utilization of vertical space. So, this treatment combination is merits consideration for commercial growers of Assam to bring about timely and quality flower production of Dendrobium cv. Sonia.