Orchid viruses are one of the “known mysteries” in orchid growing and collection. They are widely recognized as a concern; any thorough repotting demo or orchid culture talk implores the audience to take precautions to disinfect cutting tools, pots, and prevent cross-contamination on potting benches. Yet very few people systematically test for viruses in their orchid collections or request a test at purchase. Only recently have virus tests for Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV) been required at local orchid society auctions in our area.
While 17 viral pathogens have been confirmed to infect orchids (pers. comm., Janet Lamborn, Agdia, Inc.), it is believed that over 95% of infections are from CymMV and ORSV (pers. comm., Kay Klausing). These are the two “home testable” orchid viruses, and the viruses which I will discuss in our findings.
For this article, I will focus on our results from virus-testing our orchid collection, and the patterns indicated. I will also add my practical suggestions, to hopefully save you time and money in the testing process. (In another article, I describe our process for orchid virus disinfection of repotting tools.)
Note: I am not presenting our orchid virus testing as a scientific study or analysis. We grow mostly species and primary hybrids of a few genera. There is nothing random or representative about our orchid collection; however, the samples of the genera are large enough to point towards some meaningful trends to consider.
Testing our entire collection for CymMV & ORSV
In my inquiries, I have found little information available on how widespread orchid viruses truly are in orchid collections and nurseries. A lack of tangible data can lead to a lot of assumptions and mythology.
I was a participant in some of the assumptions, as I describe below, and assumed a minimal risk for most of my collection. Our findings have inspired me to offer the detailed results, to encourage others to re-evaluate their expectations, and how they wish to approach dealing with orchid viruses in their collections and purchases.
In some respects, orchid viruses are a bit of an “inconvenient truth” that growers and vendors have not widely made the efforts to investigate, expose, and directly address. I’ve received quite the range of responses when reporting the virus status of an orchid after a purchase. Sometimes denial, sometimes non-response to emails, sometimes a full refund with no questions asked. Before a sale, the messages are also routinely mixed: no testing needed, no symptoms of viruses here, or viruses really aren’t that much to be concerned about. And the ubiquitous: “it is too expensive to test my plants.”
Recognizing the heterogeneity in attitudes, and frequent lack of transparency regarding virus tests, we decided to take on the time and expense of testing ALL of our blooming and near blooming size orchids to shine the light on orchid viruses effectively “hidden” in our un-tested plants. I also wished to understand the patterns of virus distribution across genera that I collect, and from different vendors, for the future considerations of our collection.
While this is a relatively small sample (365 orchids at the time of these test results), I found it large enough to observe some meaningful patterns. We did not test any seedlings deflasked within this year; they are too small and it would be necessary to use most of the plant for the test.
Species are the majority of our collection (63%), with primary hybrids (12%) and more complex hybrids making up the remainder (25%) (Graph 1).
Graph 2 summarizes the distribution of genera tested in our collection: Cattleya Alliance (4.3%), Cymbidium (21%), Dendrobium (47%), Paphiopedilum (11.2%), Phalaenopsis (3.8%), vandaceous genera (6.5%), and other genera not included in the former (3.8%). For reference, of the Dendrobiums, about half (54%) are Australian Dendrobiums.
Especial appreciation for the inspiration for our virus testing endeavor is extended to Dr. Kay Klausing, molecular biologist and president of the San Diego Orchid Society. He gave an eye-opening talk on orchid viruses to the San Francisco Orchid Society in October 2018, and shared detailed results of testing his entire 1200 plant collection. While I had already tested our entire cymbidium collection, after his talk, I realized it was time to step up and test the rest.
Starting with Cymbidiums: Assumptions and expectations about viruses
As noted above, we had long recognized the prevalence of orchid viruses in cymbidiums, due to the many decades of plant divisions passing through commercial nurseries en masse without disinfection procedures between orchids. An older grower once commented that he would divide and repot a hundred cymbidiums in a day without any hygiene or disinfection between plants. Similarly true for commercial cattleya production. I have heard numerous comments about widespread viruses in “heritage cattleyas.”
Under these conditions, it is easy to see how viruses could rapidly spread and be prevalent in older cymbidium and cattleya cultivars. Cymbidium growers in California have actively recognized this, and were instrumental in the development of the quick, “home” CymMV and ORSV test kits that most of us in the USA currently use for virus testing (Agdia Labs). One well-known California grower has a comprehensive virus policy on their website with offer of pre-testing for sales, and our local Cymbidium societies now require virus testing for plants entered into their very popular auctions.
Suffice to say, I had strong awareness of virus concerns for Cymbidiums, and we tested our entire collection, and have tested every new Cymbidium. For the initial testing of our 70 Cymbidium plants, we found six plants (8.5%) with ORSV — ALL purchased from one local grower. I describe the details with our other results below.
Our Virus Testing Process
One of the key sources of resistance to virus-testing is the cost of the CymMV/ORSV test kits from Agdia, Inc.; with shipping they are currently about $5.75 per test. While Agdia does NOT make this recommendation in their instructions with the kits, it is possible to test multiple plants with each kit. I have found it highly sensitive at detection, even with small samples, as long as the sample quality is good (enough cellular liquid content and well crushed). When testing multiple plants, I take extra care to crush each plant’s sample individually, and then thoroughly mix the buffer solution in the test kit.
My experience is comparable to Kay Klausing’s suggestion of six plants per test as optimal. With more plants and sample material, I have found the dilution of the sample in the buffer solution to be too high, and the test takes a long time to process. He noted that some members of his orchid society have successfully cut the test strips in half; I have not tried this.
There is another manufacturer of test kits from Taiwan, Regabio, but they do not have a US distributor. However, the San Diego Orchid Society placed a group order, which resulted in a substantial discount, bringing the tests to about half of the price of the Agdia tests. The Regabio test kits require a smaller sample size than the Agdia tests, and remain shelf stable for 18 months.
I used a new, disposable razor blade to obtain each sample from the plants. While it may vary by genera, I found roots to be excellent for sampling. It was easy to obtain a small piece of root and allowed for more plants to be combined into one test kit with less adverse effect on the dilution factor than leaf material (especially from thick-leaved Dendrobiums).
There is a caveat for how many plants it is useful to combine into one test. After all, if you get a positive result, then you have to start testing the orchids individually to find the one (or more) with virus. If you have a high virus prevalence in your collection, you could wind up actually using MORE test kits by combining multiple plants into one test than if you just tested each one individually.
Unfortunately, when you start testing, you have a big unknown — you do not know what percentage of your orchids are infected. However, as you proceed, you may obtain some experience to determine which plants are lower risk, and can be combined into one test with a greater likelihood of negative results. Once I saw the patterns, I started testing “high risk” orchids individually. I determined the “risk” by the age of the cultivar and the source of the plant.
It is hard to say in advance what approach will ultimately work the best for an individual grower, since each collection is so unique. I organized our testing by orchid vendor, since, from my Cymbidium testing described above, I had identified the plant source as highly correlated to positive virus test results. In Dr. Klausing’s presentation, it was notable that specific vendors also accounted for a large majority of his infected plants. I ultimately found the same.
Results & Discussion
With such a long prelude, the results of several days of work can be summarized fairly succinctly. In total, 6.8% of our collection tested positive for CymMV or ORSV. 11 orchids tested positive for CymMV, eight tested positive for ORSV, and six were positive for both CymMV and ORSV. I elaborate on these results by type, genera, and vendor in the three following graphs.
Orchids in our collection were acquired from a total of 41 different sources. However, 10 of these were purchases of only 1 plant and none of these single purchases were infected with virus. I have excluded these vendors from the following graph, and only include sources of 2+ orchids.
Three local growers accounted for most (67%) of the positive results. To my horror, I determined that 3 of 7 plants that I purchased at ONE nursery open house were infected with CymMV. All were healthy, vigorous orchids with no symptoms of virus, even in hindsight.
My appreciation and recognition of Andy’s Orchids, our second largest source of orchids: NO virus positive plants, of the 49 that I have purchased. Kay Klausing also reported no virus-positive orchids from Andy in his collection. Also notable, my largest source of orchids only resulted in 2 of 68 plants to be positive with CymMV (both older divisions/cultivars). Clearly, virus detection, disinfection, and handling practices within greenhouses are signifiant — and effective — for maintaining a virus-free nursery and sale plants.
Species orchids were the largest portion of our collection (230), and accounted for the lowest virus incidence (4.3%). Primary hybrids (44) and more complex hybrids (91) were similar in virus incidence, 9% and 12% respectively (Graph 4).
In total, there were six Cymbidiums, 10 Dendrobiums, one Sarcochilus, and eight Phalaenopsis infected with CymMV and/or ORSV (Graph 5). There were no virus infected Paphiopedilums, vandaceous, or Cattleya Alliance plants. For clarity, we do not own any orchids in the Cattleya genus; our Cattleya Alliance plants are all Leptotes, Epidendrum, Laelia, and Rhyncolaelia. I discuss each infected group below.
The only indication of cross-infection within our collection was amongst the Phalaenopsis. These were complex hybrids that resided at my husband’s company for many years, cared for by employees and myself. Disinfection of clippers after cutting flower stalks was minimal to none; when the plants were first acquired many years ago, no one even knew of orchid viruses.
The surprising result with the Phalaenopsis collection exposed one of the false assumptions that I had about orchid viruses: mericloned Phalaenopsis would be low risk for virus. Apparently, a very incorrect expectation. Seven of eight of the virus-positive Phalaenopsis were obtained from the same reputable local orchid nursery (not a grocery or box store), though originally imported from Taiwan. No other orchids that I obtained from that nursery (including Paphiopedilum, Vandaceous orchids, and Dendrobiums) were virus positive.
From what I can speculate in hindsight, 2-3 of the Phalaenopsis that I initially purchased had virus, two with CymMV and one with ORSV, and subsequently spread it to another four in the office. All were asymptomatic, flowering and growing profusely.
One infected Phalaenopsis was a mounted species (mericlone import from Taiwan), and kept separate at our house. I believe it was also likely infected upon purchase, given little to no contact with any of the other infected plants, and my strong disinfection procedures at home.
As noted above, all of the infected Cymbidiums came from one local grower and all were infected with ORSV. These included three species, one primary hybrid, and two complex hybrids.
The species and primary hybrid were older clones, and fit the pattern described earlier of being infected in the pre-virus awareness days of orchid culture. However, the complex hybrids were seed-grown at their nursery, strongly indicating transmission within their collection. Fortunately for us, our disinfection procedures prevented any apparent spread.
(I would like to note that it is possible to transmit viruses through flasking orchid seed, if the inside of the seed capsule of a virus-positive orchid is scraped and the virus material is introduced into the media. However, if the seed is shaken from the capsule, and no parent plant material is intermixed with the seed, then the resulting seedlings should be virus free.)
Dendrobiums & Sarcochilus
The 10 infected Dendrobiums came from six different growers, and all were infected only with CymMV.
Older cultivars of Dendrobiums were the stand-out (60%) amongst the infected Dendrobiums. Three of the infected Dendrobiums were divisions from old species plants and three were divisions of old primary hybrids; two of these were originally wild-collected.
Three commercial growers had two infected plants each detected. However, these included the old primary hybrids and species described above, and another older hybrid. I have purchased dozens of non-infected plants (seed grown and divisions) from these same nurseries. It appears that these plants are fairly isolated in their nurseries. With this experience, going forward, I will certainly be very careful in considering purchasing ANY older cultivars or specimens, regardless of the nursery.
One local, commercial vendor had the highest infection rate: 3 of 7 plants purchased at a recent open house. This included two mounted Dendrobium species and 1 Sarcochilus species.
The final infected Dendrobium was a primary hybrid purchased from a well-established online commercial grower. I have only purchased two orchids from this source.
Reflections on the Virus Testing Process
I can say that it was a rather trying process, watching each test to see if one of my cherished plants would test positive. That being said, I am VERY grateful to have undertaken the time and expense. I feel relief knowing undetected CymMV and ORSV infected orchids will not able to inadvertently infect other orchids in our collection, or be given/sold to another orchid grower. The thought of unknowingly spreading orchid viruses is far worse to me than the cost and effort it took to test our plants.
That being said, our disinfection and handling procedures are even more rigorous now, despite knowing the CymMV and ORSV status of our orchids. We still treat each orchid as potentially virus-infected. Why? Because each plant STILL is potentially infected with an orchid virus. There are other orchid viruses that have not been tested/identified, and always the possibility of a false negative remains. In fact, the Agdia virus test kits were recently updated to be sensitive to a previously undetected Asian strain of CymMV; therefore, we can only be assured of knowing the virus status of a plant for what is currently detectable with the available kits.
What to Do with the Virus Test Results
What to do with orchids that have tested positive for virus is a complex and often emotional question. Orchid growers have very different perspectives about retaining virused orchids in their collections. I do not make a recommendation, or imply a criticism of anyone else, in sharing how we handled our test results.
I personally do not wish to maintain orchids with viruses in my collection and will test all newcomers to ensure that we do not obtain more. A small orchid with virus will become a large orchid with virus — where will the all of the effort in growing ultimately lead? As I commented above, we do not wish to be in a position where we could spread virus to other healthy orchids in our collection, or to someone else’s collection. That is antithetical to why we grow orchids.
We disposed of all of the orchids with positive test results with four exceptions.
We decided to keep (for now at least) the two wild-collected Dendrobium natural hybrids, a large Dendrobium linguiforme specimen, and a very old Dendrobium division originating from a royal garden in Asia. We retained these plants because: 1) they had a very low risk of infecting other orchids, and 2) they were irreplaceable, with all known divisions likely also virus-infected.
We considered the risk of spreading infection from these orchids to be low because they are: 1) slow growing and well-contained, 2) reside separately from our other orchids, and 3) are infrequently repotted. When we do need to trim flower stalks, etc., I will only use a disposable razor blade. They will be repotted in a separate location on the property, away from any other orchids. Old pots, media, stakes, etc. will go directly to the garbage.
Thank you if you are still reading this long discussion! I hope that the results and my reflections will be useful to you in your orchid growing. I believe that all orchid growers can benefit from greater awareness and transparency regarding the presence of orchid viruses. If there is a down side to testing for orchid viruses, it would be finding out something that we wish was not true, i.e., identifying a virus infected plant.
I reached three key conclusions from the testing of our collection:
- Older cultivars — both species and hybrids — have the highest risk of infection
- Most virus infected plants originated from a small number (3) of local vendors
- Some genera have higher infection rates than widely realized (Phalaenopsis) and some genera (Paphiopedilum) appear to have consistently lower rates of virus infection
With regard to the low rates of infection for Paphiopedilum, at a talk by Brandon Tam, the orchid curator at Huntington Gardens in Pasadena, California, he stated that they randomly tested 300 of their 6000+ Paphiopedilum and Phragmipedium collection. He found one positive result (Phragmipedium). Especially in mixed genera collections, the risk of virus infection in Paphiopedilums is always there, but seemingly lower than other genera. Possibly this is because Paphs are seed-raised and infrequently divided compared to other genera, such as Cymbidiums and Cattleyas, reducing virus exposure over the decades.
Best wishes for your orchid growing!
A’na Sa’tara, D.Phil