Resource Book on Horticulture Nursery Management

simultaneous. The gelling agents from roots should be cleaned before the plants are
transferred into the rooting media. Moisture content or humidity around transferred
plantlets should be maintained for a better result.
Advanced Approaches: The conventional approaches are not sufficient to
acclimatize the wide range of plant species, an alternative in vitro and ex vitro approaches
can be adopted. Plantlets are pre hardened in culture vessels before being transferred into
the soil. The plants can be hardened by bringing about alterations of sugar concentration
in the culture medium. Some other means are like controlling the concentration of gelling
agents, use of antitranspirants, control of gas exchange around the plantlets, use of
growth retardants, and autotropic mode of nutrition of in vitro plantlets are also taken
care of.
Hardening Unit: The hardening unit is provided with controlled light, temperature,
relative humidity and periodic water spray system to harden (acclimatize) the nursery
plantlets before transplanting. The nursery plantlets deflasked in the laboratory are kept
in this hardening unit for 3 to 6 months for hardening before they are released into the
field for cultivation.
Hardening or Acclimatization: The successful acclimatization of
micropropagated plants and their subsequent transfer to the field is a crucial step for
commercial exploitation of in vitro technology. However, the acclimatization of
micropropagated roses was reported to be a difficult procedure because of rapid
desiccation of plantlets or their susceptibility to diseases due to high humidity. The newly
developed method of hardening, consist of cellulose plugs for support and protecting the
roots during transfer to soil, and ventilated culture vessel to improve the resistance of the
plantlets to desiccation. The plantlets thus grown showed better survival when
transferred to ex vitro conditions.
In case of banana plantlets which are being acclimatized from cultured vessels to
greenhouse, the plantlets have shoots and roots but are not yet capable of supporting
themselves in the soil, prior to acclimatization,. The rooted shoots are about 6–8 cm tall
and receive nutrients from an artificial medium that contains major nutrients. To help
acclimatize the plantlets, the caps or tops of the culture vessels are removed for a period
of at least several days. The recommendation is that a minimum of 10 days be allowed
for in vitro acclimatization.
Stages in Hardening
Primary Hardening: The micro cuttings were subjected to primary hardening in
closed mini polytunnels with 95-100% Relative Humidity (RH) for 4-5week (stage II)
and partially opened polytunnels with 65 % RH for 4-5 week (stage III).
Secondary Hardening: It is done under shade net with 45 % RH for 1 month (stage
IV). The response of micro cuttings in various rooting media is recorded as budding,
rooting and percentage survival.
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