Helped Chris with the Temperate Display - cutting back foliage on the edges that was looking weary or trodden on. Also to define shapes of planting and for them not to overcrowd each other.
It turned out that a couple of the Kalanchoe turned out to have Tomato Spotted Wilt Virus - here was pathology's response:
Thank you for the Kalanchoe samples which were passed to Plant Pathology.
The Kalanchoe velutina had powdery mildew present on it. Whilst powdery mildew is generally associated with a white powdery coating on the leaf surface, it can also cause distinct brown patches on leaves (for example powdery mildew on some Rhododendron sp. can cause brown circular markings). Powdery mildew is often most damaging when plants are stressed for example by excessively dry or wet soil, compaction, or root restriction. If the problem continues, you may wish to try spraying with a suitable fungicide such as myclobutanil, difenoconazole, tebuconazole or triticonazole according to the manufacturer’s instructions.
The Kalanchoe pubescens had circular brown scab markings and the K. blossfeldiana had green/yellow circular markings and neither had any fungal mycelium or spores present on them. A lateral flow test for four common viruses was conducted on a section from each leaf and both gave a positive result for tomato spotted wilt virus (TSWV). Symptoms for TSWV are highly variable and the host range is very wide. Unfortunately virus infections are generally systemic within the whole plant and removing symptomatic tissue will not eliminate infection in a plant. There is no control available once a plant is infected with a virus. You may therefore choose to remove and destroy any plants displaying symptoms to reduce the chance of spread to other plants. We recommend not to propagate from virus infected plants, and to follow good hygiene measures such as cleaning and disinfecting tools after use. The main vector for spread of this virus is the western flower thrip, and hence keeping thrips under control in the glasshouse is the best method of control.
Useful RHS web profiles with further information:
Impatiens necrotic spot virus and tomato spotted wilt virus: https://www.rhs.org.uk/advice/profile?PID=473.
And a more general profile on viruses which gives a bit more detail on the biology of viruses: https://www.rhs.org.uk/advice/profile?PID=188
Spraying for powdery mildew won't get rid of symptoms on old leaves but can prevent it from appearing on the new leaves. The virus could be spread by insects like thrips.
Pathology invited me to the lab to test for the virus.
We took a sample of the Kalanchoe using sterilised tools, and crushed it up with a mortar and pestle, then inserted into the test packet which had these litmus like paper indicators. With a pipette we put in an extraction buffer liquid that contains different salts to make the sample more into a solution and possible to be tested.
 |
| Photo 1: Sterilising tools. |
 |
| Photo 2: Kalanchoe specimen with a piece cut off from it for testing. In the test pack below the fluids of the plant is absorbed by different strips. The third along has two red lines present - indicating that it is Tomato Spotted Wilt Virus. |
Each litmus paper like strip picks up a particular virus present. These packs come ready made and they are made by this company called Agdia. How the strips work is a bit complex in that it is based on how antibodies, antigens and amino acids work - different viruses have different proteins present - this is a way of helping to identify them. Each strip has a different binder that picks up on this. The different viruses this one tests for is aforementioned, Impatiens Necrotic Virus, Cucumber Mosaic Virus and Tobacco Mosaic Virus.
Cut back all the leaves of Begonia rex types to the main stems, to make way for new growth. For the cane types we reduced the height to a third and thinned out.
 |
| Photo 3: Begonias that have been on display in the Corridor, Rex and Cane types to be cut back. |
 |
| Photo 4: Begonia Rex types cut back. |
- Shrubby
- Cane
- Rhizomatous
- Tuberous
- Eyelash ones