Download i. introduction

I. INTRODUCTION
Indoor plants are ranked high in landscaping industry for their ornamental value due to
shape, colour and variation of leaves and are extensively used for interior decorations. Indoor
plants gives aesthetic and biological comfort to interior spaces, when plants are kept in rooms,
relative humidity increases and this has a relaxing effect on people. Indoor plants give coolness
to eyes and tranquility to the soul, besides a source of satisfaction. For ardent garden lovers, who
live in the cities, indoor gardening is one of the few means of exercising garden adventures. For
elderly and sick people, it is a good time pass and source of recreation. A beautiful interior scape
with indoor plants is responsible for making ordinary homes into spectacular ones and office
buildings into livable places. Irrespective of whether the property has commercial or a residential
use, a room that overlooks a beautiful, rich, green landscape usually gets the most takers and is
quite conducive commercially. It also increases real estate value.
In terms of floriculture trade being done in the world, 351 million indoor plants per annum
were traded through Flora Holland flower auction with an annual turnover of €1.525 million
(`11.83 crores). Among these, foliage indoor plants like, Ficus and Dracaena which are also
among top ten indoor plants contributed a total of 30 million plants to the floriculture trade in 2013
(Anon., 2013).
Beside all these, the role of indoor plants in abating indoor pollutants cannot be
overlooked. According to United States Environmental Protection Agency indoor air can be up to
hundred times more polluted than outdoor air leading to “Sick Building Syndrome”. Research
conducted by National Aeronautics and Space Administration (NASA) corroborates the presence
of harmful volatile organic compounds such as formaldehyde, benzene, trichloroethylene in
indoor air. In 1973 they achieved tremendous success in maintaining air quality inside confined
spaces using plants since different indoor plants has the ability to absorb harmful volatile
compounds (Misra, 2011). Indoor potted-plants can reliably reduce total volatile organic
compound (TVOC) loads by 75 per cent, to below 100 parts per billion (ppb) and can also remove
indoor Cabon monoxide (CO) and sometimes, Carbon dioxide (CO2) (Tarran et al., 2007). The
NASA studies generated the recommendation to use 15 to 18 good sized houseplants to improve
air quality in an average 1800 square foot house (Janakiram and Usha, 2013).
Most foliage plants originated in the tropical and subtropical regions where they grow
under tree canopies on shaded forest floors or live on trees as epiphytes. A distinct characteristic
of many foliage plants is that they can grow at low light intensities (Chen et al., 2005). Although,
foliage plants can grow at low light intensities, the optimum photoperiod as well as light intensity
is needed to produce top quality plants and any change in light intensity is reflected in their ability
to retain the variegated or dark green foliage (Singh and Sidhu, 2006). To acclimatize in to
varying light intensities plant species change some of their anatomical and physiological features.
E.g., Aglaonema and Diffenbachia leaves assume a nearly vertical position when grown under
excessive light which reduces plant quality since surfaces of leaves cannot be viewed from side
(Misra, 2011). While many indoor plants will tolerate low light intensities as low as 0.5 kilolux (Klx)
to as high as 3.2 Klx (Bhattacharjee and De 2010), finished plants can be directly placed in
interiorscapes if produced under an appropriate light intensity or they must be acclimatized during
final production process (Chen et al., 2005).
Plants depend on light as their ultimate source of energy. Photosynthesis converts light
energy into chemical energy required for plant growth and development. Shade-tolerant plants
often have lower photosynthetic rates (on a leaf area basis) than obligate (or facultative) sun
species and light saturation in them occurs at less than 20 per cent of full sunlight (Aleric and
Kirkman, 2005; Zhang et al., 2004). Shade plants are subject to photoinhibition when exposed to
full sunlight, reducing photosynthesis efficiency, until recovery occurs under lower light levels
(Long et al., 1994).
Photosynthetically active radiation (PAR) is a part of light spectrum used for
photosynthesis and plant growth ranging from 400-700 nm wave length representing visible light.
The rate of photosynthesis peaks in most plant around 450 nm (blue light) and at 650 nm (red
light). Plants require a reasonably balance spectrum in this range, since red light alone produces
soft growth and long internodes, while blue light results in short, hard plants (Badgery-Parker,
1999).
Plants can sense the quality, quantity and direction of light and use it as a signal to
optimize their growth and development in a given environment. In addition to its role in
photosynthesis, light is involved in the natural regulation of how and where the photosynthetic
products are used with in the developing plant and in photomorphogenetic, photoperiodic and
phototropic responses. Plants use photoreceptors like phytochromes, cryptochromes to sense
and respond to changing light conditions (Oren-Shamir et al., 2001). One example is the role of
phytochromes in monitoring the Red/Far-red (R/FR) ratio as an indicator of competition from
other plants and as an initiator of changes that favour plant survival (Kasperbauer, 1994; Smith,
2000).
Since many indoor foliage plants are shade loving plants, these plants cannot be
produced and grown under open conditions and hence a shadenet house with a correct
percentage of shade factor plays an important role to create optimum climatic conditions and
enhance plant growth to its optimum. Shadenets are made of 100 per cent polyethylene interwoven thread with specialized Ultra-violet (UV) treatment with different shade intensities. It
provides partially controlled atmosphere by reducing light intensity and effective heat during day
time to crops grown under it (Anon., 2010).
Taking advantage of plants response to various wave lengths in a light source, efforts to
manipulate plant morphology and physiology using photoselective filters have been going on for
decades especially in green house environments. In this regard, use of coloured shadenets or
photo-selective nets is an emerging technological approach. On top of physical protective
functions and environmental modifications, these nets are unique as they are designed in such a
way that they both spectrally modify as well as scatter transmitted light. The colour of the net is
obtained by mixing chromatic additives to high density polyethylene (HDPE) grains before the
production of the compound (Castellano et al., 2008). In order to increase light scattering from
these nets, various light dispersive additives are added apart from chromatic additives during
manufacturing.
Photo-selective nets include ‘Coloured-colour nets’ (e.g., red, yellow, green, blue net
products) and “neutral-colour nets” (e.g., pearl, white and grey). Unlike black shade nets, the
coloured nets differentially and specifically modify the incident light in either, ultra-violet (UV), the
visible or the far red (FR) spectral regions and at the same time enhance the relative content of
scattered light and or absorb part of infra-red (IR) radiation. Unlike plastic films, the nets are
composed of both holes and plastic threads. Therefore, the fraction of light that passes freely
through the holes remains unchanged in its quality, while the fraction hitting the threads comes
out of the net both spectrally modified and scattered. The spectral manipulation promotes desired
physiological responses, while light scattering improves light penetration in to the plant canopy
(Shahak et al., 2004; Shahak, 2008).
Indoor plants are produced and marketed by various nursery-men in Karnataka and the
demand for quality indoor plants by interior-scapers and other consumers are gaining popularity
especially in Bangalore. Presently, shadenets are available in different colours viz., white, black,
red, blue, yellow and green and also in combinations. Recently, some nursery-men have started
to use these coloured shadenets as a covering material in shadenet houses. Even though these
nets have been tested in over 30 countries and for about more than 56 crops with promising
results (Ganelevin, 2008) there is limited consistent scientific data or evidence to say that a
particular coloured shadenet suits best for the production of indoor plants with desired growth
habit.
As research in this field is limited in India and global level, especially for indoor plants and
keeping the above points in view, in order to generate information for the local conditions, the
present investigation was taken up, with the following objectives.
1. To evaluate the effect of different coloured shadenets on growth and performance of
indoor foliage plants.
2. To assess variations in different pigment levels as influenced by different coloured
shadenets.
3. To identify the best shadenet for good growth and quality of indoor plants.