Have you ever wondered how the plants sitting on a garden centre bench are actually created? During my visit to Danziger in Israel, Lab Manager Osnat gave me all the answers! From tiny shards of plants to voluptuous flowering garden specimens, here’s the journey of Petunia ‘Queen of Hearts’.
1. Obtaining the material
In Danziger, there is an in vitro (tissue culture) bank, in which thousands of varieties are being grown and maintained as a vegetative, disease free genetic stock. Laboratory staff start with plant material, taken as cuttings from the ‘mother plants’!
These mother plants are often grown in large poly tunnels, in large pots, and their only role in life is to provide cutting material. The lab staff take around 50 different cuttings from the same plant for the initial stage of tissue culture: introduction and establishment of aseptic culture.
Once the tissue culture plant has established, it can last for up to 20 years and yield hundreds and thousands of pieces of plant material. It’s almost like a plant library, and this is where all the stock of Danziger plant varieties are grown and maintained.
Tissue culture micropropagation is chosen as a propagation method as it gives a genetically identical plant to the original, and reduces the passing on of any disease.
2. Disinfection for hygiene
For healthy plants, hygiene is super important. The staff then need to disinfect the greenhouse plant material, they do this with a bleach solution, which contains 1.5% sodium hypochlorite. After that, the plants are washed through with sterile water (all the work is done inside a sterile environment in a biological hood) and placed into a gloopy substance. This medium contains agar, which stabilises the plants inside a tube, it also contains sugars, vitamins, minerals – all the elements that the plant needs to start growing! Because they have taken the plant out of the soil, staff need to emulate the nutrients that the plant gets from soil and mimic that in the artificial medium.
Staff then observe the plant material for two to three weeks to check plants haven’t developed any unwanted bacteria or fungi. If the plants appear to be healthy, we move to the second stage.
3. The Multiplication Stage
To maximise the amount of the tissue culture material, staff then divide the cutting into parts, collecting up all the auxiliary buds and shoots. One plant can yield around five plant parts, all genetically identical to the original. So rather than being able to grow one plant from the cutting, you can grow five! Each of these shards of material is called an “explant”. They are then placed into a new medium with the same substance mix as before.
Each variety has a unique quantity of plants that it can yield in a specific timeline (this is known its multiplication rate). For example, staff know that five Petunia tissue culture plants can yield 20 new plants after one month. This information helps them to predict timings for shipments; if they need to ship 1000 tissue culture plants, they know when to start the multiplication process in order to achieve that number.
4. The Rooting Stage
The aim is to get the plants to root in the medium before they are transferred to a conventional soil medium, i.e compost. Sometimes staff want rooting to happen faster, so they add auxin (a growth hormone) to the media.
Once there are roots well-established on the tiny plants, they start to resemble a conventional plant, rather than an odd test-tube baby!
5. Moving the plant to soil
The first part of this stage is called ‘hardening’. Here, the rooted plant is taken out of the medium and placed into the soil, however this is a process that needs to be carried out VERY gently and gradually, as the plant has effectively been grown in laboratory conditions, and kept in boxes with 100% humidity! The stomata cells (cells which allow gas exchange) in the leaves are completely open when moved from the agar medium. If staff were to take these plants out of their medium straight away and leave them to survive in the soil without any cover, they would most likely die.
Staff place the plants into their soil medium and cover them with plastic covers for around 10 days. After the plant begins to grow new leaves, and the roots can be seen to be growing, they are planted into bigger pots.
6. Final stage
Now, the plant that originated from the tissue culture tube is transferred to a very clean greenhouse, which is protected by a net against the insects. The plant then begins a new life as a next generation mother plant, from which cuttings are harvested fresh. Those cuttings will be sent to the rooting stations (or direct to self-rooting nurseries) in order to produce plug plantlets, which are later planted in flower pots or module trays, and finally transferred to different selling points all over the world!!
Michael has been involved with gardening and plants since he was just five years old. He is a self-professed Plant Geek, and was listed in the Sunday Times top 20 most influential people in the gardening world, thanks to his plant hunter role at Thompson & Morgan.
Michael was responsible for new plant introductions such as the Egg and Chips plant and the FuchsiaBerry and keeps busy travelling the world in search of new plants as well as lecturing worldwide, including stints in Japan. He is very active on social media – so why not give him a follow at @mr_plantgeek or Facebook – and writes a plant-focused Substack called Grow This, Not That.