Abstract
Efficient long-term management for the production of high-quality Cymbidium plants is required as these orchids generally require 3–4 years of vegetative growth to allow flowering. This study was conducted to investigate the optimal substrate moisture levels to efficiently produce young cymbidium using a soil moisture sensor-based automated irrigation system over 42 weeks of vegetative growth. One-year-old cymbidium “Hoshino Shizuku” plantlets were grown in coir dust substrate at four levels of volumetric water content (0.25, 0.35, 0.45, and 0.55 m3·m−3). At harvest, the numbers of leaves and pseudobulbs, and the chlorophyll content of the cymbidiums did not differ among the four θ threshold treatments. However, plants grown at 0.25 m3·m−3 had significantly smaller leaves, pseudobulbs, and biomass than those at the other θ threshold treatments. Although the lower θ decreased the photosynthetic parameters, such as the net photosynthesis, stomatal conductance, and transpiration, there were no differences in the maximum quantum yield of photosystem II, indicating that the reduction in net photosynthesis is mostly mediated by stomatal closure. Although the net photosynthesis at θ of 0.35 m3·m−3 was also lower than that at 0.55 m3·m−3 treatment, biomass was significantly lower only at 0.25 m3·m−3 treatment, suggesting that a critical growth reduction by the water deficit occurred for the cymbidium at 0.25 m3·m−3. As the θ threshold increased, the total irrigation amount significantly increased, which inversely decreased the water use efficiency. Although the plants grown at 0.25 m3·m−3 had the highest water use efficiency (WUE) and substrate electrical conductivity they showed significantly reduced growth compared to other θ threshold treatments, and thus this was not a reliable θ threshold level for producing high (visual) quality cymbidium. Overall, the 0.35 and 0.45 m3·m−3 threshold treatments provided appropriate moisture levels for high-quality cymbidium production with high water use efficiency.
Highlights
Orchids are one of the most commercial floricultural crops and are distributed throughout the world
The price of orchids has been lowered due to technological advances in micropropagation, they are still relatively expensive for flowers as, for example, cymbidium requires cultivation periods of ca. 4–5 years to grow from seedlings to cut flowers or potted plants; efficient long-term management is necessary for profitable cymbidium production [2]
Previous studies have reported that orchids such as cymbidium, Cattleya, and Oncidium withstand drought stress because of their irrigation unique roots, with
Summary
Orchids are one of the most commercial floricultural crops and are distributed throughout the world. Most cymbidium growers use bark as the substrate to avoid over wet conditions, preventing rhizosphere diseases, including root rot, black rot, or bacterial infections, this substrate, which has a low water-holding capacity, requires more frequent irrigation with a huge drainage fraction [6]. Alternative substrates with a higher waterholding capacity have been investigated to enhance water and nutrient use efficiency; better cymbidium growth was subsequently observed in cymbidium grown in carbonized rice hull [7], peat moss [8], and Hyuga pumice [9] than those grown in the bark. Most orchid growers are reluctant to change their substrate because of the difficulty of irrigation management on substrates with a high water-holding capacity. Most standard type commercial cymbidiums are classified as terrestrial (C3 plant) which prefer slightly moistened substrate conditions than epiphytic (CAM plant) cymbidium [10], most cymbidium growers in Korea usually irrigate with timer-based irrigation using a sprinkler, and approximately 75% of the water with dissolved fertilizer is leached every irrigation [11]
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