Once more with feeling: Pathogen is not the disease – Lifestyle – Akron Beacon Journal


Spring has arrived, and forsythia and corneliancherry dogwood are blooming. Spring peppers chorus at Johnson Woods Nature Preserve near Orrville. Crocus, out for some time, will soon be joined by daffodils and then later, tulips. Silver maple flowers are passing, red maples are bright against the sky, and soon enough, sugar maples will join the party.

Classes at Ohio State University started again, virtually, after a doubled spring break. Students in my “Sustainable Landscape Maintenance” class this week, chose to learn about ferns and other non-seed plants.

Ferns are becoming increasingly popular for gardeners. Refreshing to connect with the student, albeit electronically. I think we all missed each other. It was a chance to get viruses and viral diseases out of our minds.

Which brings up a question that keeps demanding discussion: pathogen or disease? What’s in a term or a name? Clarity of thought and communication.

When discussing plant diseases, I always make a point, ad infinitum or ad nauseum (your choice), that the pathogen is not the disease. This is a key precept of the Plant Disease Triangle, that for an infectious plant disease to occur, three things must coincide: a virulent pathogen, a susceptible host plant, and an environment conducive to disease.

Disease is a process. Rose black spot will not occur unless there is the virulent fungal pathogen (Diplocarpon rosae), a susceptible host (certain roses), and the number of hours of wet foliage at a given temperature.

Planting roses resistant to rose black spot, for example, is a great disease management strategy because it means that not all three components of the disease triangle are present. Of course, the pathogen, working 24/7 like everything in nature, tends to mutate and to genetically recombine during reproduction, overcoming resistance to the pathogen in certain roses, so the eternal “Nature red in tooth and claw” always applies.

Other strategies for rose black spot disease target the pathogen: sanitation and fungicides. Managing environmental conditions is yet another strategy. Since leaf wetness duration is a key for this disease, use sprinkler irrigation to limit water on leaves and if you decide not to, at least water during the mid-part of the day to encourage leaf drying before night affects relative humidity, which rises as temperatures fall. Nature of course intervenes if it is a particularly rainy season.

Following that trip down plant disease lane, we return to the current focus of all our lives: COVID-19. Recently, it occurred to me that I did not know what it stood for: the CO (corona) seemed obvious, and the VI (for virus) seemed obvious, but what is the D? Duh, it is for D (disease), and the 19 is for its discovery in 2019. COVID-19 is the name for the disease. The pathogen’s name, the term for the virus, is SARS-CoV-2.

According to the CDC, there are currently seven coronavirus pathogens (characterized by crownlike spikes on the surface of the virus particle) known to infect humans.

Four cause common cold symptoms, and the remainder:

• SARS-CoV causes SARS: Severe Acute Respiratory Syndrome

• MERS-CoV causes MERS: Middle East Respiratory Syndrome

• And now SARS-CoV-2, causing COVID-19.

Be safe. And remember the words of Voltaire, at the conclusion of “Candide”: “Cultivate your (own) garden.” Help control rose black spot by cleaning up any diseased tissue that overwintered and help manage COVID-19 by staying home and practicing social distancing.

Crocus

But enough of viruses, for now.

When croci were first trying to come out in Northeast Ohio two weeks ago (seems like months), I was preparing a talk on “Having Fun With Plant Families.” I had plenty of material already, but a few hours before the talk, reviewing some crocus poetry, I pondered, hmm, what is the family of the genus Crocus? That started me down the garden path of learning and relearning about Crocus, including some very important distinctions.

First, Crocus is in the iris family, the Iridaceae. I knew Crocus was a monocot, the class of plants with single cotyledons (seed leaves), along with grasses, sedges, and more closely, lilies. But I had not remembered about the Iridaceae; it is a family with more than 80 genera (a family is a group of related genera) and more than 1,700 species.

These genera include Iris, Gladiolus, Sisyrinchium (the lovely blue-eyedgrass – not really a grass), and Crocus.

A distinctive feature of genera in the Iridaceae is that the male flower parts include three pollen-bearing stamens and the female flower parts consist of a pollen-receiving stigma atop thestalk-like style, often three-parted, with the ovary at the base. Remember this.

For now, let us turn back to Crocus. Species in the genus are native from central Europe to China, with many of the garden croci we plant and are enjoying now being the “Dutch” crocus, Crocus vernus.

The autumn crocus, Crocus sativus, is the source of saffron, the lovely golden- to orangish-yellow-colored spice that is so wonderfully used in cuisine, such as the Spanish dish paella, in French bouillabaisse, and in Italian risotto. It is also used as a food coloring, a dye, and in fabrics. Saffron threads are stigmas of Crocus sativus. Now, remember that Crocus, as a genus in the Iridaceae, has three stamens and one three-parted style.

But there is another crocus-like plant that blooms in autumn, and this is where I realized I was unclear about the identity and particulars of this other plant that is called “Autumn crocus.”

It should be called Autumncrocus or Autumn-crocus to signify that it is not a true member of the genus Crocus. It is also commonly called naked ladies or meadow-saffron. It is the plant Colchicum autumnale, a late-in-the-growing-season bloomer, with the true “Autumn crocus,” Crocus sativus, the plant that produces saffron.

They are different plants, and Colchicum is not even in the same plant family. It is a member of the Colchicaceae rather than the Iridaceae. Importantly, Colchicum autumnale and related plants produce colchicine and colchicine-related products.

Colchicine is used to treat gout and certain other medical conditions, and Autumn-crocus has been used for millennia to treat swollen joints. According to Wikipedia, with medical references cited and checked, in 2019, colchicine available generically in the UK by the National Health System cost just over 7 pounds ($8.17 U.S) for a month’s supply; in the U.S. the wholesale cost for that supply is just over $250.

Colchicine is also a mutagen long-used by plant breeders to produce tetraploids and octoploids (multiples of chromosomes) resulting, for example, in double flowers on crabapples. Colchicine used for medical conditions is a classic case of “the dose makes the poison”; it is highly toxic if used therapeutically at even mild dosages in excess of recommended rates.

Some have also posited it could be a carcinogen and with other developmental and reproductive toxicities, but the verdict is unclear.

Colchicum is a genus with more than 160 species. Colchicum autumnale is native to Great Britain and Ireland. The Colchicaceae has 15 or so genera (there are always arguments among classifiers) and more than 280 species.  Other genera in the family are less well-known, but include Ornithoglossum and Iphigenia.

Greek mythology followers will remember Iphigenia as being sacrificed after her father King Agamemnon had slain the sacred deer of the goddess Artemis and lying to Iphigenia that she was to marry that heel Achilles. Or that Artemis saved Iphigenia at the last moment, later to become a priestess for Artemis.

Note: How can you easily tell the difference between Crocus and Colchicum, or the difference between genera in the Iridaceae and the Colchidaceae? Crocus and the Iridaceae genera have three stamens and one style. Colchicum and the Colchidaceae genera have six stamens and three styles. Now, come fall, we can practice identifying the difference between Autumn crocus and Autumncrocus!

So, now I certainly know more about Crocus and hope you do too. Finally, for fun, while putting this together, I also found some additional quotes and poems about croci.

Ah, Google.

There were a number of outstanding crocus poems from luminaries such as Oscar Wilde and Johann Wolfgang von Goethe all from AZ Quotes. Check it out. Here is my favorite, prosaic rather than poetic, example, from one of my favorite early 20th century wits, the Algonquin Round Tabler, Robert Benchley.

“You might think that after thousands of years of coming up too soon and getting frozen, the crocus family would have had a little sense knocked into it.”

Crocus, and gardeners, and all us, do well to be ever hopeful. Not quite to the tune of Voltaire’s other famous words from Candide, spoken by the overly rosy Pangloss: “It is the best of all possible worlds.”

We should be optimistic, but we must do our part to make it better.



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