Symptoms The disease mainly affects stems, stalks and capsules. At the early stage of disease, the leaves were yellow, sunny leaves closed, cloudy days were still able to develop, the stem base tissues were soft rot, the epidermis fell off, and the whole plant died seriously. When the soil moisture is high, white filaments of mycelium can be seen covering the diseased area and the surrounding ground. After that, rapeseed-like white sclerotia nucleus is produced, and finally the color of the soil is changed to dark brown. The rhizome tissue became infected and fibrous, eventually causing the plants to die and die.
The pathogen, Sclerotium rolfsii Sacc., is known as S. sclerotiorum and belongs to the fungus Subgenie Fungi. Sexuality is Athelia rolfsii (Curzi) Tu. & Kimbrough. It is a basidiomycotina fungus. It rarely occurs under natural conditions. In life history, two distinct vegetative mycelium and sclerotia are produced by asexual generation. The vegetative mycelium produced during the growth period is white, with a diameter of 5.5-8.5Î¼m. There are obvious connective hyphae and each section has two nuclei. Before the sclerotia are produced, a finer white hyphae with a diameter of 3.0-5.0Î¼m can be produced. The cell wall is thin, with a septum, an unlinked connection, and often 3-12 parallel bundles. Mycelial cell wall is fibrous, average thickness
0.1-0.3Î¼m, the activity of acid phosphohydrolyzing enzymes in the 40-200Î¼m before the mycelial tip, is mostly surrounded by various vacuoles or lysosomes. In addition, the nucleus, nucleolus, endoplasmic reticulum, and flanks are visible. Wait. The membrane inside the hyphae is a typical barrel diaphragm with a total of 5 layers. The white tinea corporis is formed by 3-12 mycelial bundles arranged in parallel. At this time, the mycelium grows lateral branches first, then branches for multiple branches, gradually becomes spherical, and the hyphae have mutually attracting substances. When the hyphae form a sclerotium bud, there is a substance that can attract each other between the hyphae. After the axillary buds develop, whether they can continue to develop into sclerotia depends on whether the bacteria itself has enough energy. When there is no specific influence factor, sclerotia are gradually formed.
Phytophthora infestans are divided into two major groups: A-type mycelium grows sparsely, producing a wider circle of sclerotium at the edge of the culture dish and more sclerotia. The R-type mycelium grows thicker and produces fewer sclerotia at the edge of the dish. The sclerotia begins with the formation of axillary buds from a small group of mycelium collections. There are loose, terminal, and mycelial bundles in three forms, from irregular branches, and there will be a few pseudo-flexible cell components in the nearby mycelium. The composition of this mycelium begins to adhere closely, and hyphae fusion may also occur. The sclerotia of the whitefly disease can be structurally divided into four parts: the outermost layer is a thick cortex formed by dark-brown thick-walled cells; the inside is a shell, which is formed by connecting 2-4 layers of thick-walled cells; Inside is the subcutaneous layer, composed of 6-8 layers of thick-walled cells; the innermost layer is the medullary part, composed of mycelial elongated cells loosely, filled with some small particles with higher electron density, which may be the storage of carbohydrates. And some black particles wrapped in a film. Each cell in the sclerotia has two nuclei. Mature sclerotium skin contains melanin that is resistant to harsh environments.
Transmission routes and pathogenic conditions The bacterium sclerotia or mycelium are overwintering in the soil or on the diseased body, and most of them are distributed in the top soil layer of 1-2 cm. The germination rate was significantly reduced with sclerotia below 2.5 cm, and almost no germination was observed at 7 cm in the soil. The sclerotia germinate the next year, producing hyphae, invading from the epidermis or wound of the base of the plant's rhizome, and invading the ovary handle or capsule. Seeds can also be carried. Bacteria spread in the field by running water or insects. High-temperature, high-humidity, soil viscosity, poor drainage, low-lying land, and rainy years are prone to disease. As soon as the rain turned, the diseased plant quickly withered and died. Continuous cropping and early sowing are heavy.
Prevention and control methods (1) Dispose of the diseased body promptly after harvest and deep-dip. (2) More than 3 years rotation with rice, wheat, corn and other gramineous crops. (3) Advocate the use of compost or decomposed organic fertilizer made from fermented bacteria to improve soil permeability. (4) Appropriate late sowing of spring peanuts, clear seedlings at seedling stage, and improved resistance to disease. (5) Select disease-free seeds and use 50% carbendazim WP with seed weight of 0.5% for seed dressing. (6) After the onset of disease, use 50% seed dressing double powder 1kg mixed fine dry soil 15kg made of medicine soil cover disease hole, each hole medication soil 75g. (7) Early onset of spraying 50% benomyl WP or 50% acetaminophen WP or 50% procymidone (WP) wettable powder, 20% chlorhexidine PM 1000-1500 Times of liquid, spray 100-200ml for each good liquid.
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