Fytophthora, or water mold – a threat to crops, but also wild plants


In late 2023 and early 2024, precipitation totals in many areas of Poland not only returned to the multi-year norm, but even exceeded it. After many months of below-average groundwater, long-term recovery of groundwater supplies would require a much longer period of heavy rainfall, but local floodplains are already forming in places, reminiscent of the condition that was typical of pre-winter as recently as the second half of the last century. This, of course, pleases most naturalists, but there are also those who pay attention to the other side of the coin. Phytopathologist Wojciech Pusz notes that spillages facilitate the spread of fytophthora spores, resulting in fytophthorosis [1].

Phytophthora – a disease caused by nematodes, not by fungi

Phytophthora (Phytophthora) is a genus of larvae. This group of organisms was for decades considered to be the so-called “”A” group. lower mushrooms. In customary English nomenclature, it is referred to as water molds, although their representatives can live on land and do not necessarily form moldy sheepskins. Practitioners of plant protection in the cultured sense of the word (more recently also called plant medicine) still categorize the diseases they cause as fungal diseases, and categorize the agents for their control as fungicides.

In fact, lungworms are very distantly related to fungi, including mold. Closer to them are algae, such as diatoms, goldworms or brown algae, and a little farther away are cryptomonads, dinoflagellates or haptophytes (the notorious golden alga is one of them), as well as periwinkles and various types of rootworms. If an agent described as a fungicide acts on both nematodes and true molds, it means that this name is an unjustified refinement, because the substance most likely kills virtually everything.

Phytophthora infestans, one of the Phytophthora species, is well known as a pathogen that attacks potatoes and tomatoes. As an invasive species outside Central America since the early 19th century. across the United States, and since the middle in Europe, has often caused catastrophic damage to potato crops. He was the cause of the Great Famine, which resulted in the deaths of about one million Irish and a similar number of them emigrating, resulting in a 20 percent population decline in Ireland.

Because of the role that phytophthora plays in agriculture, research on it has become the flywheel not only of phytopathology, but of mycology in general. In the first quarter of the 20th century. already distinguished twenty species of the genus, and after a century ten times as many are known. An avalanche of newly described species has occurred in the last two decades. That’s when its evolutionary history, which dates back 140 million years and is closely linked to the history of vascular plants, was better understood. Coevolution has led to a peculiar synchronization of some molecular mechanisms [2].

Water carries pathogens, including potato blight

Phytophthora spores are in the form of a swimmer, or a cell with a tendril. Their spread requires the presence of water, although sometimes moist soil is sufficient, and the spores of the most resistant species, such as just Phytophthora infestans, can be carried by the wind. Therefore, phytophthora affects potatoes and tomatoes, which are not wetland plants. Nevertheless, the presence of water on the soil surface facilitates the survival and transport of tides.

Fytophthora threatens not only crops, but also wild plants

Potato blight is the best known, but not the only phytophthora. The second edition of the Polish Names of Crop Diseases [3] gives half a hundred more diseases of this genesis. Phytophthora infestans is responsible for two of them, but Phytophthora cactorum and Phytophthora cryptogea have seven each to their credit. As the name suggests, Phytophthora cactorum is known to infect cacti, but in Poland it also attacks fruit trees and shrubs, strawberries, rhubarb and rhododendrons. At least when it comes to species familiar to farmers or gardeners.

However, since it attacks currants growing in orchards, wild shrubs growing in Polish alder forests, i.e., periodically waterlogged alder forests, may just as well suffer. The alder forests are also home to scythe trees, the garden varieties of which, known as irises, are infected by Phytophthora cryptogea and Phytophthora nicotianae. In swamp forests, as in crops, various species of phytophthora can attack blueberries and cranberries.

Foresters are also familiar with Phytophthora cactorum, as it infects birches, beeches, oaks, rowans, maples, larches, lindens, alders, pines and spruces in Polish conditions. Of course, other species of this louse are also capable of this, especially Phytophthora citricola. As you can see, among the listed undergrowth and stand plants, quite a few are found in alder, riparian or swamp forests that are at least periodically wet. Their root zone is surrounded by water where tides can reside, and under such conditions phytophthora will develop rapidly.

Infected water is a source of pathogens

Many fungi have trouble breaking through the barriers created by plants, but phytophthora floaters can penetrate quite healthy roots, starting from their youngest parts. The roots must take up water, so they must not be too tight a barrier. In addition, Phytophthora infestans can also penetrate the stomata of leaves. Once it succeeds in infecting the roots, its shreds spread, which can open the way for other parasites, such as the fireworm.

Fytophthora will develop even more easily when the plant is weakened. Therefore, it is favored by extreme weather events. When it’s overburdened by drought, it begins to produce new roots after rainfall, an easy target for attack. When the rains are intense, they lead to flooding. Perhaps this is the main reason for the increasing number of phytophthorae observed.

In addition, watering crops with water taken straight from a river, lake, ditch or puddle is riskier than using disinfected tap water, though of course much more expensive. And against the recommended saving of treated water. Threats to the safety of food produced by the agricultural sector from pathogen-infected waters are also highlighted in a report by the United Nations Food and Agriculture Organization. Food and Agriculture Organization (FAO).

Global warming is thought to favor microbial growth, and phytophthora physiology is adapted to weather extremes. Currently, human spread of the pest with agricultural products is still considered the main factor responsible for the increase in recorded phytophthora. However, it affects more than just crops. Since the 1990s. last century is also intensifying in forest ecosystems and, for example, in heathlands [2].

In the article, I used, among other things. From the works:

[ 1] https://www.facebook.com/permalink.php?story_fbid=pfbid02A3J3SvmekHXbFiANkxZbasXV8fhcYtzCiyziYFSs9gtpub5UkYCmf6odHbhio5Ubl&id=100093674104485

[2] Brasier C., Scanu B., Cooke D. et al. Phytophthora: an ancient, historic, biologically and structurally cohesive and evolutionarily successful generic concept in need of preservation. IMA-Fungus 13, 12 (2022). https://doi.org/10.1186/s43008-022-00097-z

[3] Borecki Z., Schollenberger M. (eds.), 2017. Polish names for crop diseases. Published. 2. Polish Phytopathological Society, Poznań. ISBN 978-83-948769-0-6

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