Clonal propagation: what it is and how it is done

SLSU Clonal Nursery uses both the mist and non-mist system during the rooting stage of the plants.

Much like animals can be cloned like the ever-controversial Dolly the Sheep, the same can be done with plants. Some plants may even benefit from cloning.

Clonal propagation is the process of reproducing genetically-identical plants through asexual means. This is recommended for species that are difficult to propagate due to an irregular supply of their seeds. This is especially true for dipterocarps, which take more than a decade before their first flowering, have irregular fruiting seasons, and have short viability of seeds. Clonal propagation could also benefit plant species that are endangered in the wild.

In 2012, the Department of Environment and Natural Resources partnered with 27 state universities and colleges (SUCs) to produce quality planting material as part of the National Greening Program. DENR granted each SUC P3.5 million for the construction of clonal nurseries. One of these state universities is the Southern Luzon State University (SLSU) in Lucban, Quezon. Kathreena Engay-Gutierrez, the former project head of the SLSU Clonal Nursery, spoke with Agriculture Online to explain how clonal propagation is done.

Selecting individual plus trees

The process starts by mapping out the individual plus trees (IPTs) with favorable phenotypic characteristics in an area. In choosing these trees, foresters are guided by standard guidelines set out in the Department of Agriculture Order No. 2010-11 which states that in assessing potential IPTs, the foresters should evaluate the tree’s total height, diameter at breast height, stem straightness, stem forking, stem circularity, tree health, branch angle, branch thickness, and pruning characteristics.

Once IPTs have been identified, parts of the tree like shoots and stems are collected so they can be regrown in a clonal nursery.

Hedge garden

A hedge garden is used to collect cuttings for propagation.

Collected parts from a plus tree are regrown in a hedge garden, also called a ramet garden. The purpose of maintaining a hedge garden is to have a steady source of cuttings that are used to propagate more clones.

Plants in a hedge garden are grown at a distance of a half meter across and sideways from one another. The plants grown here are cut to at a certain height so new cuttings could continuously grow.

Once collected, the cuttings are taken into a laboratory where they are cleaned with distilled water and a sterilizing concentration. The cuttings are then soaked for one hour in a solution of 1-Naphthaleneacetic acid (NAA) and Indolebutyric acid (IBA), depending on the species. These are hormones that promote the growth of roots. During the process, foresters ensure they do not contaminate the cuttings by wearing face masks and other protective gear.

Rooting stage

Cuttings need two to three months to take root in the medium.

Cuttings are planted in two propagation systems: mist and non-mist systems. The mist system involves planting the cuttings on a rooting bed inside a chamber with a mechanized spraying system. While cuttings are in their sticking and callusing stage, the chamber automatically sprays water for five to eight seconds every five to 10 minutes for the entire day and night. After three to four days, spraying is reduced to three to five seconds every 10 to 20 minutes while spraying is reduced or completely avoided at night depending on the weather.

The non-mist system, on the other hand, involves planting the cuttings on polyethylene bags. The watering of plants is done manually with this system. 

The rooting media used by the SLSU Clonal Nursery is 1:1 coco coir and river sand. Cuttings need two to three months to take root in the medium, with dipterocarps taking up to six months.

Foresters can check if the cuttings have taken root by nudging the cutting to see if it has anchored to the medium. Another way is to check if new leaves have formed. However, the formation of new leaves can sometimes only be a reaction of plants to stress and is not a completely reliable indicator that roots have grown.

Recovery and hardening stage

Plants are stored in the recovery area for three to five months.

Plants that were grown in the rooting chamber are transplanted into polyethylene bags and transferred to the recovery area. For the SLSU Clonal Nursery, this area is located in a dedicated greenhouse. The recovery stage takes three to five months.

It is during the recovery stage that a biofertilizer called mycorrhiza is applied to the garden soil. This is a fungus that has a symbiotic relationship with plants. They live on root systems and help plants absorb more nutrients and water. 

Before plants are deployed to planting sites, they are hardened for one to two months. At this stage, plants are exposed to harsh conditions like direct sunlight or placed outside greenhouses so they can acclimatize to the environment of their planting site.

Clonal propagation has allowed SUCs like SLSU to propagate endangered plant species like batikuling (Litsea leytensis) and makaasim (Syzygium nitidum). The technique allows them to conserve species that would otherwise struggle to reproduce in the wild given the effect of human activities on the environment.

Photos by Jerome Sagcal

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