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The mystery of Aphanomyces euteiches: Why does this pathogen make crops so vulnerable?
Aphanomyces euteiches, a water mold or entomophilous fungus, has caused great distress in the agricultural community as a plant pathogen, particularly causing root rot in many soybean crops. This disease affects the United States, Europe, Australia, New Zealand and Japan, affecting the growth and yield of many crops.
Symptoms of root rot may vary between hosts, but generally manifest as a reduction in root size and function, ultimately resulting in poor plant growth and yellowing of leaves.
Host and symptoms
Aphanomyces euteiches can infect a variety of leguminous plants, including peas, alfalfa, lentils and red kidney beans, beans, red clover and white clover. Of particular note is Aphanomyces euteiches f.sp. pisi, the primary pathogen causing pea root rot and the most economically damaging form. In North America, the A. euteiches genome exhibits host specificity, whereas this phenomenon has not been observed in Europe.
Because A. euteiches is a root-infecting pathogen, first symptoms usually occur in the root and stem tissues below the soil surface. Infected roots often have a gray and water-soaked appearance that eventually evolves into a soft and honey-brown or dark brown color. This infection causes a reduction in root size and function, including reduced nodule formation, which in turn affects water and nutrient uptake, causing secondary symptoms in the aboveground parts.
The frequent patterns of infected plants in fields are often associated with areas of poorly drained soil, which may be related to soil compaction, soil texture (high clay content), or excessive moisture.
Disease cycle
Aphanomyces root rot is a monocyclic disease, with only one infection cycle per crop during the growing season. Although A. euteiches can infect a host at any time, infection usually begins when seedlings germinate. The main source of infection by the pathogen is oospores found in soil or on infected plant debris.
Oospores begin to germinate after sensing chemical signals released by the roots of their new host plant. Germination can be divided into direct and indirect. In direct germination, the hyphae produced by the oospores directly penetrate the cells of the host plant roots; in indirect germination, the sporangia formed by the oospores release zoospores, which then attach to the cells of the host and then germinate. .
Under optimal conditions, an A. euteiches infection can show symptoms within 10 days, and oospores can form within 7 to 14 days. After oospores form, they enter a dormant state and can survive in the soil for more than ten years.
Environmental factors
Aphanomyces is a soil-borne disease whose entire life cycle occurs in the roots of the host and the surrounding soil. A. euteiches is most active in warm, moist soil conditions but can also survive in moderate temperature ranges. Infection usually occurs during the seedling stage of the host plant, especially within the temperature range of 22 to 28 degrees Celsius.
So, the presence of stagnant water in the soil increases the host's risk of infection because it makes it easier for zoospores to move onto host cells.
Management measures
The most effective management measure farmers can take is to use disease-tolerant varieties. Disease-resistant varieties have been identified on the market in alfalfa, beans, peas and red clover. Although the effectiveness of chemical control is affected by environmental factors, it is also important to use well-drained soils and soft soils to avoid infected soils.
In addition to crop rotation, soil testing and drainage management are important management practices because oospores can survive in the soil for many years. According to one study, the abundance of A. euteiches decreases when infected plant assemblages exhibit significant mycorrhizal development.
Excessive use of nitrogen and phosphorus fertilizers and repeated tillage may reduce mycorrhizal development, so it is critical to find treatment options to reduce the impact of this pathogen.
History and Importance
Aphanomyces euteiches was first described by Drexler in 1925, by which time the pathogen was causing root rot problems in Wisconsin and the American Midwest, particularly in pea production. Due to the widespread nature of the disease, large economic losses have become increasingly severe over time.
Through continued research into the pathogen, agricultural experts still face the challenge of how to effectively manage A. euteiches. Despite advances in modern crop breeding, farmers still need to be cautious and alert to the possible impacts of A. euteiches. In the face of such a cunning pathogen, how do we balance the management of yield and disease risk in agricultural practices?
