2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
White rot, otherwise called sclerotinosis, is considered an extremely harmful and very common bean disease. To a large extent, the development of this ill-fated misfortune is facilitated by too frequent precipitation in conjunction with a sufficiently high air humidity. And the most susceptible to white rot are plants that lodge and are noticeably weakened by various unfavorable conditions. As a result of the defeat by this ailment, both individual shoots and plants as a whole gradually dry out and wither
A few words about the disease
White rot attacks all overground organs in growing beans: beans, flowers and leaves with stalks. Initially, the manifestation of this disease is noted near the soil surface in the very foundations of the plants, as well as on those organs that are in direct contact with the soil.
On the stems attacked by white rot, local formation of a white pathogenic mycelium begins. Often, the infected areas become discolored and dry out, and some time later the whole plant withers and dies. In most cases, the stems turn yellow and rot rather quickly, and their softening tissues are characterized by fragility and gradually die.
On beans, the initial symptoms of white rot are manifested in the formation of watery wet specks, which subsequently slowly begin to become covered with an unpleasant, cotton-like white mycelium. When dry weather is established, those tissues on which the superficial mycelium has not yet had time to form, begin to stain in yellowish-greenish, yellowish-reddish or chocolate-brown tones. Against the background of grassy-green areas not affected by the disease, such a color is very noticeable. And if the beans were infected at the ripening stage, they quickly become saturated with moisture, and the color of their tissues gradually changes to pale rusty.
On almost all infected organs of growing beans, intensive formation of fungal sclerotia begins, designed to preserve the infection in extremely unfavorable conditions. At the same time, their configuration can be completely different: irregular, elongated or rounded. Initially, sclerotia are characterized by a white color, and after some time they turn black. They are most commonly found inside infected beans and stems. And a pathogenic sclerocial mass is produced from the fungal mycelium filling the inter-seed spaces.
Bean seeds, attacked by white rot, discolor and lose their luster. Also, in some cases, a whitish airborne pathogenic mycelium is visible on them. And subsequently, on the surface of the seeds, the formation of black semi-substrate sclerotia begins, which can be seen with the naked eye.
The causative agent of white rot of beans is a pathogenic fungus called Sclerotinia sclerotiorum (Lib.) De Bary, which affects a huge number of field and vegetable crops. The sclerotia of this fungus germinate either mycelially or with the formation of apothecia, including bags with pathogenic ascospores. Both mycelium and ascospores can provoke primary infection of growing crops. And throughout the growing season, the spread of the pathogen occurs by fragments of the mycelium. Nevertheless, infection often occurs when the organs of the bean that are not affected by the disease come into contact with the affected ones.
The fungus-causative agent is preserved either on the affected seeds in the form of mycelium, or on plant residues in the soil in the form of sclerotia.
How to fight
To noticeably reduce the susceptibility of beans to such an unpleasant ailment, it is extremely important to follow the rules of crop rotation, planting beans only after crops that are not affected by white rot. Seeds for sowing should be taken only free from infection, and it is recommended to dress them before sowing. It is equally important to observe the optimal sowing time, as well as systematically provide the growing beans with a balanced mineral nutrition, the doses of potassium and phosphorus in which should be increased. And in case of severe soil contamination, it should be periodically disinfected.
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