Resource Book on Horticulture Nursery Management

Temperature: The temperature range for optimal plant development is 25–35° C.
Air temperatures above 40°C must be avoided. Additional heating needs to be provided
to propagation beds where temperature drops below 20° C in winter. Heating cables or
mats which provide bottom heat can easily be installed. Temperatures need to be most
carefully monitored and held inside the recommended range during seed germination,
rooting of cuttings and graft union formation.
Gas Exchange: Rooting, cuttings and germinating seedlings have high respiration
rates. This means that oxygen is consumed and carbon dioxide released. The proper
exchange of these gases is very important for good root development. In heavy soils and
under waterlogged conditions, exchange of gases does not take place efficiently, resulting
in accumulation of toxic amounts of CO2 in the root zone. This condition hampers the
healthy root growth.
Plants need to take up carbon dioxide for assimilation through the stomata on the
leaves. Plants stressed by drought or nutrient deficiency have their stomata closed and
cannot assimilate CO2 properly. This results in retarded photosynthesis and growth.
Atmospheric air contains about 0.03% CO2 and 21% O2. For specialized purposes, plants
can be grown under elevated CO2 levels of up to 3% to increase production.
In enclosed structures, the ambient level of CO2 can drop till the assimilation
through the stomatas is slowed down. Ventilating the structure briefly can avoid this.
Electricity: Electricity should be available in the nursery so that equipment such as
ventilators, heating cables, electrical balances, and data loggers can be installed. If it is
not possible to connect the nursery to the main power line, consider using
nonconventional systems of electrification.
6.2.4 Production and Hardening in Plant Production
The hardening or acclimatization, process begins while the plantlets are still in vitro
i.e. growing in the culture vessels. Acclimatization is the physiological adaptation of a
plant or animal to changes in climate or environment such as light, temperature or
altitude.
The tissue culture plants need acclimatization or hardening before they are
transferred in the field. The acclimatization is necessary because there is vast variation in
the environment of plants in vitro conditions and environment in the field. In culture
vessels the in vitro plants are exposed to high humidity, hetrotrophic mode of nutrition,
high ethylene concentration and constant temperature throughout the year. These
conditions lead to the development of plants having low epicuticular wax, low stomatal
density and stomatal malfunction, which make these plants more vulnerable to mortality
in field conditions. To prevent this mortality, it is must to harden or acclimatize these
tissue cultured plants.
Approaches for Hardening of Plants: To have success in hardening of tissue
culture plants, the following approaches are adopted: plantlets to be hardened should
have a balanced proportion of roots and shoots. Appropriate rooting media should be
selected for establishment of plants ex vitro. They should be provided a balanced
nutrition for survival of rooted plantlets. The rooting and acclimatization should be
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