MSc

The study entitled “Physiological approaches for enhancing the ex vitro establishment of tissue cultured orchid (Phalaenopsis sp.)” was undertaken during 2017-2019, at College of Agriculture, Vellayani, Thiruvananthapuram, with the objective to study the physiological changes that occur during ex vitro establishment of orchid Phalaenopsis sp. and to find out measures to overcome the field mortality rate and improve propagation efficiency.
The experiment was laid out in completely randomized block design with three replications of ten treatments as well as a control. In vitro derived plantlets of Phalaenopsis sp. obtained from Biotechnology and Model Floriculture Centre, Kazhakuttam were used for the study. Ten treatments were T1 and T2 (plantlet dip with triazole @ 5ppm and 10 ppm respectively), T3 and T4 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm after 15 days of planting and plantlet dip with triazole @ 10 ppm + foliar application of triazole @ 5ppm after 15 days of planting respectively) , T5 and T6 (plantlets providing with 40-50% light intensity & 60-70% humidity and 40-50% light intensity & 80-90% humidity respectively) T7 and T8 (plantlets providing with 70-80% light intensity & 60-70% humidity and plantlets providing with 70-80% light intensity and 80-90% humidity respectively) , T9 (plantlet dip of PGPR mix І -5%) , T10 (root zone application of arbuscular mycorrhizal fungi -5g/plantlet) and a control (C). The crop was maintained in the hardening chamber for 70 days and observations were taken at 15, 30,45 and 60 days of ex vitro transfer.
Results revealed that growth regulators, growth stimulants, light and humidity had significant effect on physiological, morphological, biochemical, biometric and anatomical characters during the ex vitro establishment of tissue cultured orchid Phalaenopsis sp.
During their ex vitro establishment, physiological parameters like specific leaf area and photosynthetic rate showed significantly higher response at all the four stages of observation, in the treatment provided with 40-50% light intensity and 80-90% humidity (T6) whereas transpiration rate was the lowest in T3 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm after 15 days of planting and plantlet dip with triazole @ 10 ppm). Among the stomatal characters, stomatal index was not significantly affected by growth regulators, light intensity, humidity and growth stimulants. However, highest stomatal frequency was recorded in T3 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm, after 15 days of planting).
Plantlets treated with arbuscular mycorrhizal fungi (T10) recorded the highest plant height during 15 and 30 DAP. However at 45 and 60 DAP, plantlets which were provided with 40-50% light intensity and 80-90% humidity (T6) recorded the highest plant height. Number of leaves per plantlet and survival percentage were also found highest in T6. But in the treatment, T3 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm) maximum number of roots was observed at all the four stages of observation.
The results also showed that chlorophyll a and total chlorophyll content of the leaves were maximum in T3 whereas in T6, the highest chlorophyll b and carotenoid content were found at all the four stages of observation. Also T3 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm) recorded the highest protein content and carbohydrate content.
Leaf area and root length were also found to be significantly higher in T6 (plantlets provided with 40-50% light intensity and 80-90% humidity). Root shoot ratio was the highest in T9 at 15 and 30 DAP and T3 recorded the highest root shoot ratio at 45 and 60 DAP. Fresh weight and dry weight of the plantlets were recorded maximum in T10 (plantlets treated with arbuscular mycorrhizal fungi).
There was no significant difference in the number of mesophyll layers of orchid leaves during the ex vitro establishment. However, cuticle thickness was found highest in T3 (plantlet dip with triazole @ 5 ppm + foliar application of triazole @ 5ppm, after 15 days).
Survival percentage is considered to be the most important factor during the ex vitro establishment of tissue cultured orchids. Among the different treatments, T6 (plantlets provided with 40-50% light intensity and 80-90% humidity) recorded the highest survival percentage at all the four stages of observation (80, 76, 72, 66 percentage respectively) compared to control.
Considering the physiological, morphological, biochemical, biometric and anatomical characters, treatment T6 (plantlets provided with 40-50% light intensity and 80-90% humidity) is adjudged as the best physiological approach to overcome field mortality and improve propagation efficiency of tissue cultured orchid Phalaenopsis sp. during ex vitro establishment.