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War at the Roots: How do Aphanomyces infect people?
Aphanomyces euteiches, a saprolegnia or fungal plant pathogen, is primarily responsible for causing root rot. This pathogen mainly affects various leguminous plants such as peas and alfalfa. In infected plants, the overall function of the roots is generally severely affected, leading to reduced plant growth or even the death of the entire crop. This disease is an important problem in agriculture in the United States, Europe, Australia, New Zealand and Japan, and how to effectively manage this pathogen has become a challenge for farmers in various countries.
Host and its symptoms
The hosts of Aphanomyces euteiches are mainly leguminous plants, including peas (Pisum sativum), alfalfa (Medicago sativa), red beans (Phaseolus vulgaris), French bean (Vicia faba), red clover (Trifolium pratense) and white clover (Trifolium repens). Among them, Aphanomyces euteiches f.sp. pisi is considered to be the main cause of pea root rot, which is one of the most serious forms of economic losses.
The main symptoms caused by Aphanomyces root rot include a reduction in root size and function, which leads to yellowing and shrinkage of the leaves of the plant.
In North America, A. euteiches exhibits host specificity that is less evident in Europe. Because A. euteiches is a root-causing pathogen, the main symptoms appear in the roots and stem tissue below the soil. Infected roots are usually gray and water-soaked, eventually becoming soft and changing color to honey or dark brown. Infected plants will eventually develop secondary symptoms above ground due to reduced root function, including yellowing of young shoots and necrosis of stem/root rachis, slow plant growth, and wilting of leaves.
Disease cycle
Aphanomyces root rot is a monocyclic disease, causing only one cycle of infection per growing season. Infection usually occurs as early as the emergence of seedlings. The main source of infection is oocysts that lie dormant in the soil or in infected plant debris. Oocysts germinate in response to chemical signals in the roots of new host plants and can directly invade host cells at the root tip or release zoospores as spores.
In the process of direct germination, the hyphae produced by the oocysts can directly penetrate the root tip cells of the host; in the indirect germination, sporangia are produced, and the zoospores form capsules on the host cells and then germinate. .
The growth of Aphanomyces euteiches is best suited to warm, moist soil conditions, with host plant infection being most apparent within a temperature range of 22 to 28 degrees. Because zoospores require moisture to move easily, standing water in the soil increases the chance of infection. After infection, symptom development prefers warm and dry soil conditions.
Management measures
The most effective management technique for farmers is the use of disease-resistant varieties. The presence of disease-resistant varieties has been identified in beans, peas and red clover. However, the challenge of establishing acceptable resistant varieties remains due to differences in consumer demand. Furthermore, the effectiveness of chemical suppression depends on environmental factors such as temperature and soil moisture.
Good soil drainage, field soil testing, and avoiding planting of susceptible crops in fields with confirmed A. euteiches infection are all effective management practices.
Crop rotation can delay the accumulation problem of A. euteiches, but because oocysts can survive in the soil for more than ten years, rotation cannot effectively eradicate the pathogen. Once high levels of A. euteiches are detected in a field, planting sensitive hosts in that field should be avoided.
History and Importance
Aphanomyces euteiches was first described in 1925, by which time the disease had caused long-term problems in pea production in the American Midwest. Over time, the impact of A. euteiches has spread to Europe, Australia, New Zealand, and Japan. As an important pathogen causing economic losses, Aphanomyces root rot usually severely affects regional crop production, leading to changes in local economic models. For example, pea production has shifted from the Midwest to drier states because climate conditions in those areas are not conducive to the survival of A. euteiches, but it remains a concern.
For agricultural producers, therefore, ongoing monitoring and implementation of management measures will be key to ensuring crop health. In future agriculture, how to deal with these root diseases more effectively will be a common issue in crop production?
