Next Growers Group Meeting will be Saturday 3rd August. With Spring approaching the main topic of the afternoon will be potting – Theory and Practice. We aim to set you up with all you need to know to start the season on the right footing.
Last month we covered pests and Diseases with special attention to virus in orchids. Over the past decades I have been involved in Orchid Virus studies sponsored by the AOC, exchange of information with local and overseas nurseries and conducted and / or been privy to the results of many thousands of virus tests. Following is information about virus in orchids we feel valuable to your success. Also are a number of links to further information if you are interested.
WHAT IS AN ORCHID VIRUS?
A virus is a small infective agent that consists of a nucleic acid molecule (genetic material) surrounded by a protein coat in an envelope of lipids. It is able to multiply itself only in the living tissue of a host and may have a detrimental effect. Viruses are microscopic and much smaller than bacteria (commonly 100th the size and 10,000 times smaller than a grain of salt). In addition to multiplying in a host they can also sometimes mutate (and have more serious effect and / or infect other hosts). There is no cure once an orchid is infected.
HOW MANY VIRUSES INFECT ORCHIDS?
There are now more than 30 viruses which have been reported to infect orchids. The older, most common of these are Odontoglossum ringspot virus (ORSV) and Cymbidium mosaic virus (CyMV). Other newer viruses reported include CymMV, DenMV, PhCSV, CyRSV, CMV, OFV and many more. It is not a case of your orchid is “Virused”, but more importantly, due to your acquisition and cultural practices, how many viruses you have accumulated.
SYMPTOMS and TESTING
Symptoms of virus can express in the flower and / or leaves. There is a huge variability of symptoms and many may also be associated with other disease, cultural practice and environmental conditions. Symptoms may include colour break of flowers, chlorotic or necrotic lesions and mosaics, and also vary widely between different genera. Other common symptoms include reduced vigor, flowers not lasting as long and less prolific, having “bad season’ of irregular flowering and growth, and necrotic streaking of flowers as they age. It is very difficult to accurately diagnose virus by visual symptoms alone.
There are various methods of testing for virus from inexpensive to very expensive. Simple inexpensive tests include serological assay (ELISA) and more expensive and less available tests include transmission electron microscopy and RTPCR. The commonly available tests are only for a couple of viruses (ORSV and CyMV). Accuracy of test results depends on a number of factors including sample taken, preparation of sample, false negatives and experience of tester. The sample should come from tissue of the new growth where virus concentration will be highest. It is necessary to repeat after a month of check if virus concentration increased or was a false negative etc. For a grower to say that they have “tested for virus” is both simplistic and naïve. It is not physically nor financially practical to test for ALL viruses with their resources.
Many plants may test positive for various viruses and grow vigorously, flower prolifically and show no visible symptoms at all. This is not a problem within itself unless your cultural and / or management practices spread this to other more susceptible plants in your collection and / or those of another grower. It is safest to assume that all orchids are virused and practice minimization and management practices.
HOW ARE ORCHID VIRUSES TRANSMITTED and SPREAD?
Obviously, in the first instance, you purchased, acquired or were gifted a plant infected with virus. It is time proven that the “cheapest”, “best bargain” etc. plant will end up being the most expensive plant in your collection. You can simply accumulate more virused plants and more different viruses by your acquisition practice.
Viruses are spread in sap or fluid from infected plants to healthy ones. For this to happen there has to be another agent to assist. Most commonly this is the grower themselves. Virus is transferred when dividing, repotting, cutting flowers etc. by infected sap on hands, cutting tools, utensils and handling area.
Chewing and sucking insects can also mechanically transmit many viruses very effectively when moving from one plant to another with infected sap. Proven insect transmitters include thrips, aphids and mites. It has been shown pretty dramatically in cut flower nurseries just how fast these can transit a number of viruses. Not monitoring and having effective control measures for such insects will allow for rapid spread.
HOW TO CONTROL and MANAGE VIRUS IN YOUR ORCHIDS
|A.||Manage the introduction of virus
The many various sources of orchids also have different levels of virus risk associated. By risk assessing the source, ordering handling and potting will minimize transmission, even in the absence of using other controls. Your orchids should be potted or handled from lowest risk first to the hightest risk last. Following is ranking of virus risk plant sources from highest to lowest risk.
|1.||Deceased / Run down collections
Usually plants have been neglected and not maintained to high standard for some time. There is a high probability insects have gone out of control and transmitted virus to remaining plants.
|2.||Orchid Society plant sales / Markets
Unfortunately, despite statements of policy that plants sold must be “clean, free of disease and established”, this is often not the case. It is not uncommon to see plants at plant sales and markets with colour break and obvious virus symptoms present. Often these are just “put under the table” so as not to offend the member selling.
|3.||Mass Market outlets / Internet
These sources are now where most orchids are purchased. My experience has been that the trained horticulturist or staff at the Service counter have little or no knowledge nor interest in orchid viruses. Internet, well? There is very little information about integrity of the source for you to assess.
|4.||The oldest plant in your collection
The plant that you have had for the longest period of time is also the one that has been repotted, divided, handled the most number of times. It has also been exposed to the longest period of possible insect transmission.
If the mother plant from which the mericlone is produced is virused then all the subsequent mericlones from it will also be virused (even though they may look like innocent little babies!). Mericlones reproduced from plants that are decades old and have not been produced from a fresh, original mother plant will be of higher risk. Mericlones produced from a recent new hybrid, original mother plant will be of lower risk.
|6.||Nurseries / Growers with proven virus knowledge and management
These sources are now where the least number of orchids are purchased. There are still many nurseries and growers that do have good knowledge and practice virus minimization and management.
Orchids produced from seed (particularly if the parent plants are virus free) are generally virus free. It is possible for some viruses to be transmitted through a hybrid seed pod, but this is currently not very common. Hybrids that have been grown on with little dividing in an insect free environment are very low risk.
|B.||Sterilizing, handling and cultural practice
|1.||There are a number of effective methods of sterilizing potting and handling tools.
– 5% sodium triphosphate (Steri Kleen) solution
– 10% commercial sodium hypochlorite (Bleach) solution
– 2% sodium hydroxide solution
– thoroughly flaming with a propane torch
|2.||Use multiple secateurs or cutting implements. If you have 3 – 4 pairs of secateurs in the sterilizing solution use only one pair on each plant repotting. When finished, place it last in the container and begin next plant with a fresh pair. Rotating in order secateurs used will ensure that they have been in the solution for the minimum 5 minutes to be effective.|
|3.||Use only new or sterilized pots and potting materials.|
|4.||Wash hands with soapy water or sterilizing solution between plants.|
|5.||Place a sheet of newspaper on potting area when dividing plants. After repotting remove with all materials, discard and replace with a fresh sheet for next plant.|
|6.||Do not have your orchids overcrowded and intergrown.|
|7.||Segregate high-risk plants from low risk plants and order potting and handling according to risk status.|
|8.||Keep effective control of chewing and sucking insects.|
|C.||If in doubt – throw it out
If you have any suspicion that a plant is affected by virus, then it almost certainly will be. Giving it another go, or placing it in “isolation” is just prolonging the inevitable and exposing the rest of your orchids to risk. It is better practice to sacrifice the few, to save the many.
THE GOOD NEWS
This information about virus in orchids should not lead you to discouragement and despair. I have Crohn’s disease and my Specialist Doctor of many years retired last year. My new, young, meticulous Specialist subjected me to extensive immunological testing (draining half my blood it seemed!), in the remote case that in the future I had serious problems and required immunosuppressive drugs. Testing revealed that I had been immunized against many viruses over past years. Also, in the past I had contracted many more viruses – all undiagnosed (and survived). Finally, I tested positive to Tuberculosis. After freaking out, I was referred to a Specialist Infectious Disease Doctor in a major hospital. Extensive further tests, x-rays and scans revealed that the test result was a false positive!
I am still alive and thriving, so are my orchids.
Further useful information
- St Augustine Orchid Society – orchid Viruses https://staugorchidsociety.org/culturepests-viruses.htm
- Orchid viruses in Taiwan and their control strategies
- American Orchid Society – virus http://www.aos.org/orchids/orchid-pests-diseases/virus.aspx
Thank you for your support
Ross and Liz