Regulation of flowering in phalaenopsis orchids

Abstract

Studies on ‘Regulation of flowering in Phalaenopsis orchid’ were conducted in the Department of Pomology and Floriculture, College of Horticulture, Vellanikkara from November 2010 to April 2012. The main objectives were to evaluate cut flower and pot plant varieties of Phalaenopsis hybrids under two microclimatic conditions, to observe their flowering behaviour with respect to the weather elements and to study the effect of cultural practices on flowering and floral characters Orchidaceae is the largest family in the plant kingdom with over 25,000 species in over 600 genera. Despite the diversity, very few genera like Cymbidium, Phalaenopsis, Dendrobium, Oncidium and Cattleya are ranked high commercially. The genus has around 80 species and more than 40,000 hybrids. It is a short stemmed epiphytic monopodial orchid with Crassulacean Acid Metabolism (CAM) pathway of photosynthesis. Based on floral characters, phalaenopsis are broadly classified as grandiflora (cut flower) and multiflora (pot plant) types. Grandiflora types have long, arching inflorescence with large flowers, whereas, the multiflora types have short, branched inflorescence with numerous smaller sized flowers. Phalaenopsis is now among the most valuable flowers used as cut flower and as pot plant. As a part of the study, phalaenopsis varieties were evaluated under two different growing systems, viz., top ventilated rain-shelter and fan and pad system of greenhouse. Vegetative growth was better in rain-shelter whereas longer flowering period and higher flower count were obtained under fan and pad system. In an attempt to induce flowering by exposing to lower temperature, plants were taken to Nellaimpathy, having an altitude of 1050 meters, and were kept for different periods. Keeping for three weeks was the best in terms of inflorescence induction as compared to control. Subsequently, comparable situation was provided in an AC room. Plants kept for two weeks initiated inflorescence. Nutrient and growth regulator treatments had no significant impact on growth and flowering. Pruning of spent inflorescence induced new inflorescence and the best treatment was pruning above the first node. Commonly used media for growing phalaenopsis are coconut husk chips and coconut husk bits, along with charcoal and tile bits. Use of sphagnum moss has been reported from other countries only as media for good moisture retention. In the present study, plants grown in sphagnum moss were significantly superior to coconut husk chips and coconut husk bits as media, both in terms of vegetative and floral attributes. It was high in chlorophyll content along with high N, Mg, S, Fe and Mn, which are responsible for photosynthesis. N fixing bacteria Klebsiella pneumonia and Bacillus thuringensis were also found in plants grown using sphagnum moss. Post harvest studies conducted to evaluate the longevity of floret and spike in plain water indicated differences among varieties. Var. Mimi had maximum inflorescence longevity and variety Roxenne the minimum. Physiological studies showed stomatal conductance, net CO2 assimilation reaching peak at 4am. Stomatal density was higher on the abaxial leaf surface in all varieties. Titable acidity as malic acid accumulation was higher in rain-shelter compared to fan and pad, indicating better growth.