Issue 6 Horticulture Spring 2002
A Poetics of Plant Pathology
Disease has troubled plants since early time. According to Cynthia Westcott’s Plant Disease Handbook, “fossil remains suggest that plant diseases were present on earth before man himself.” It took much longer to recognize, classify, and name diseases; biologists assigning technical terms for plant pathogens refered to Latin and Greek root words when they did. Common disease names, although often descriptive, tend to be anything but prosaic. Reading a pathology text, one might confuse it with a manifesto for some future poetics of entropy.
Anthracnose of Potato: stems and stolons following wilt
The pathology texts generally describe the contraction of disease, initial symptoms, and ultimately the complete destruction of the plant (if a deadly disease is involved). Brief sections of most texts mention chemical, organic, and cultural control of disease, but they do not describe the improving condition of the plant. Only seemingly entropic deterioration is detailed. Even passages dealing with pathogens alone seem to imply some other decaying world. And, in fact, they do. They reveal microscopic worlds we are unaware of until the decay of disease exposes them. Even if the disease being catalogued is benign, it usually sounds threatening.Apiosporina collinsii. Witches’ Broom of Serviceberry ... widespread. Perennial mycelium stimulates the development of numerous stout branches into a broom. A sooty growth on underside of leaves is first olive brown, then black. Numerous globose, beadlike, black perithecia appear in late summer.1
When the end of the passage reads, “The damage to the host is not serious,” it comes as something of a surprise.
A description of a bacterial pathogen can also suggest the kind of “flattened time” proposed by Robert Smithson, where all periods, from prehistory to the distant future, exist simultaneously. Or, a Brazil-type future that is weirdly retro:Ascomycetes, Dothideales, Dothideaceae.
Asci are in locules, without well-marked perithecial walls, immersed in a massive, carbonaceous stroma, erumpent and superficial at maturity.2
Granted, this is a place swarming with life, in contrast to Smithson’s crystalline, geological world.
A few Fungi Imperfecti (imperfect fungi, in which only the asexual spore stage is known) of the Phoma family comprise the following poetic pathogens—Fungi Imperfecti, Sphaeropsidales, Sphaerioidaceae
Pycnidia dark, ostiolate, lenticular to globose, immersed in host tissue, erumpent or with short beak piercing the epidermis; conidiophores short or obsolete; conidia small, 1-celled, hyaline, ovate to elongate.3
Pathology texts are a foreign language with ordinary words popping up sporadically in a familiar syntax, which seduces us into believing that they are in a language we know. The words become hieroglyphs, which we attempt to translate in context. Botanists and biologists write directly to those who know, or at least have an idea, of what they are talking about. Maybe only other professionals do. By way of introduction to her 843-page handbook,4 intended for both the layperson and the professional, Westcott notes:Don’t let all the scientific names worry you. It is the only way to make this a quick and easy reference, for there are very few common names of plant diseases that can be used without confusion. It works just like the telephone book. While thumbing your way down to Smith, John, you don’t worry about spelling Smiecinski, C., that you pass on the way.5
As there are countless varieties of pathogens and diseases offering an etymologically rich world, it would be impossible to provide a complete survey here. The ordinary potato alone has the potential to contract over 100 diseases. It has been suggested that modern plant pathology and public funding of disease research began after the Irish potato famine of the mid-1800s, with the realization of the devastating effects such a blight could have.6
Since that time, a growing number of potato diseases have been identified, including but not limited to Anthracnose, or Black Dot Disease; a variety of bacterial diseases including Bacterial Blackleg, Ring Rot, Soft Rot, Wilt; Blights (which can be Early, Late, Southern); Nematodes Golden, Root Knot, Lesion, Tuber, Ring, Sting; Nonparasitic afflictions including Black Heart, Blackening before and after Cooking, Chlorosis (Tip blight), Checking (Skin scurf), Dimple, Elephant Hide, Fasciation, Giant Hill, Glassy End, Growth Cracks, Hollow Heart, Hopperburn, Internal Brown Spot, Knobbiness, Mahogany Browning, Marginal Browning, Ozone Injury, Pitting, Pointed Ends, Psyllid Yellows, Scald, Stem Necrosis, Tipburn. They can contract Powdery Mildew, Charcoal Rot, Gray Mold Rot, Watery Pink Rot, Root Rot, Silver Scurf Rot, Watery Leak Rot, Scab; any number of viruses, Apical Leaf Roll, Purple-Top, Aucuba Mosaic, Calico, Crinkle, Vein Banding, Witches’ Broom, Yellow Dwarf, Tobacco Ring Spot, Potato Corky Ring Spot; and Potato Wart and Wilt.7
In general, “[p]lant diseases may be necrotic [nekros, dead], with dying or death of cells, tissues, or organs; hypoplastic [hypo, less than], resulting in dwarfing or stunting; or hyperplastic [hyper, excessive], with an overgrowth of plant tissue, as in crown gall or club foot.”8 Primary plant pathogens are bacteria, fungi, nematodes, viruses, and physiological disturbances (i.e., excessive heat or cold; too much or too little water).
Anthracnose, one of the most general disease categories affecting a wide variety of plants, comes from the Greek anthrax (carbuncle)9 and nosos (disease). Everything from potatoes, turnips, and peas to orchids can be affected by this condition. Its two main permutations are a necrotic spotting (dark, dead areas) and raised borders around depressed lesions. Initially, anthracnose denoted a single disease of grape plants (caused by the fungus Sphaceloma ampelina) in France that had the latter condition. The term originated with the attempt to differentiate between two diseases, both previously known as charbon. Later, diseases of other plants, which were incorrectly determined to be caused by the same fungus, were also given the name anthracnose. Eventually the term came to refer to any condition of necrotic spot or lesion. Today, the disease is often “accompanied by dieback and usually caused by a Gloeosporium or a Colletotrichum, imperfect fungi producing slime spores oozing out of fruiting bodies (acervuli) in wet, pinkish pustules.”10
Potato Anthracnose is caused by Colletotrichum atramentarium. In this case, “the black dots embedded in epidermal cells, inside hollow stems and on tubers, are sclerotia to carry the fungus over winter and to produce conidia the following spring.”11 Even if most of us already avoided the black spots in potatoes, the above text offers definite impetus to cut them out. It may be fairly common knowledge that “epidermal” has something to do with the skin. “Inside hollow stems and on tubers”—well, not everyone may know that tubers are the potatoes, but used in context, somehow we get the idea anyway. So we know the black dots of athracnose are on or in the potato. An ordinary Webster’s dictionary tells us that in certain fungi, “sclerotia” (Gr. skleros, hard) is “a hardened weblike, black or reddish-brown mass of threads in which food material is stored.” And “conidia” (Gr. konis, dust) is, “in botany, a small asexual spore occurring in certain fungi.” So the black dots are basically a nest with food to support the fungi next spring. Definitely not what we want in our mashed potatoes.
The color black figures prominently in the terminology of plant pathology, with nearly every disease leading to some variation of brown or black spot, ring, mold, or smut. Bloec, blac (Old English), blah-, blach- (Old High German), “a word of difficult history. In [Old English], found also ... with long vowel blace, blacan, and thus confused with [its opposite] blac, shining, white.”12
Blackleg is a bacterial disease of potatoes caused by Bacillus phytophthorus. Confusingly, Phoma lingam is a fungus that troubles the mustard family and results in Blackleg of Crucifers (Crux, crucis, a cross, and ferre, to bear). This cross to bear is the lot of the plant order Cruciferae, those “bearing flowers with four equal petals arranged crosswise,” according to the OED. This condition is also known as Foot Rot, or Phoma Wilt. Cabbage varieties, cauliflower, Brussels sprouts, garden cress, kale, kohlrabi, mustard, rape, radish, rutabaga, and turnip are all affected. And Phoma betae delivers blackleg to sugar beets.13
In plant pathology, blackleg is descriptive—the base of the stem, where it touches the earth, becomes depressed and turns black once the lesion has encircled it. This condition was first recorded in Germany in 1791, in France in 1849, and in the United States in 1910. Around that time, “Blackleg” was also a slang word used to describe a distemper affecting calves in England, as well as a variety of social circumstances. In general, it meant any laborer who would work for someone whose normal work force was on strike, or, someone who would sell bread or milk, for instance, at a lower price than others. “Short for Black-leg ..., of persons or of work performed by ‘blackleg’ labour. Hence, in extended use, of work boycotted by trade unions during a dispute, also of products, supplies, etc., which they refuse to handle.”14
The fungus Aspergillus niger (common in soil and on dead plant material) nurtures Black Mold of Onion, which can occur in the field during growth or while in storage. Also affected are potatoes, shallots, and apples. Aspergillum is the perforated container or brush for sprinkling holy water. From aspergere: “In the Roman Catholic Church the sprinkling of altar, clergy, and people with holy water before High Mass.”15 Aspergillus is a “genus of microscopic fungi [a black mold] resembling the holy-water sprinkler in appearance, growing on decayed organic matter.”16 Niger = black. The primary symptom is a black discoloration of tissue. Initially, the outer scales may become streaked or spotted with dark areas, often around the neck. Finally, the entire bulb becomes blackened and shriveled. The same fungus causes Fig Smut and Crown Rot of Peanut, among other diseases.
Ultimately, the entire life cycle of any vegetable crop is a battle with the poetics, or forces, of entropy. There is a cycle of growth with the potential for disease. If no disease occurs and the potato, for example, reaches maturity, the plant top must be killed in order to arrest tuber growth and allow skin formation.17 Then it must be removed from the field. If it is successfully harvested it becomes a question of proper storage to discourage rot before it is either eaten as, say, mashed potatoes or potatoes dauphinoise, or returned to the soil as seed for its shot at next year’s crop.
Susan Swenson is a writer, as well as editor and publisher of Pierogi Press, a literary/arts journal based in Brooklyn, NY.
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© 2002 Cabinet Magazine