Fusarium wilt

Fusarium wilt is one of the main diseases of melons and occurs throughout the country. It mainly occurs on cucumbers and watermelons, and its annual loss is calculated as the rate of dead plants, which is about 10-30%. The physiological differentiation of Fusarium oxysporum is very obvious. Several physiological races have been identified in China, Japan and the United States. Our country has already identified new races different from the original race from cucumbers. Given that cucumber is the main victim of Fusarium, and most of it is constrained by a strong virulent physiological race, the focus of this section is on cucumbers. (I) Pathogen infestation of cucumber fusarium wilt is caused by infection with Fusarium oxysporum. It belongs to the genus Aspergillus subfamily of the genus Fusarium in the classification of fungi. It produces a large number of flocculent mycelium that damages the host. A large number of sickle-shaped spore-like conidiospores and ovary-like conidiospores are transmitted and infected. In the life of a pathogen, it can go through winter, infestation, damage, and spread through several forms of mycelium, chlamydospore, sclerotia, and conidia. In the absence of the host, it exists in the soil and manure in the form of insects, chlamydospores, or sclerotia. In the second year, when spring arrives and the temperature rises, the seeds and seedlings of the host appear in the soil. These overwintering germs become the primary source of infection for the field host. It invades the host tissue through the wound in the root or from the micropores at the tip of the root hair. After a certain propagation activity inside and outside the root cell, it enters the vascular bundle as the liquid nutrient in the root is transported in vivo. Continuing reproduction and development within the catheter, resulting in obstruction of vascular bundles. At the same time, secrete some enzymes to digest the cells, destroy and block the host's counseling organization, causing the wilting and death of the host's vine. Cucumber Fusarium oxysporum is a very stubborn bacterium that can live in the soil in vitro for 5-6 years if it does not meet its host life. Its chlamydospores or sclerotia, even though it has passed through the digestive tract of livestock, can also survive. Continue to maintain invasive activity. The surviving bacteria in the soil are the main primary infestation source for cucumber damage, and the bacteria are also present on the seeds, but the prevalence of bacteria is relatively small, with a probability of only 0.5-3%. Because of the different ways of infection, the time from infection to disease varies greatly. According to the experiments of the vegetable institute of Shandong Academy of Agricultural Sciences, artificial inoculation with different concentrations of spore suspensions resulted in inconsistent incubation periods. Seedlings inoculated with the radicle root method can be infected within 7-10 days. Inoculation with the bacteria liquid film into the roots of the soil will require 16-25 days to see the onset, and inoculation with the bacteria soil will take more than one month. The test method of inserting seeds into bacterial soil has more practical significance. The disease-resistant strains of the disease-resistant strains are 10-20% and the susceptible strains are 20-30%. According to another test, the inactivated spore suspension of pathogens can reach 90% or more within 16 months. Host infection is restricted by some conditions. The main environmental conditions are: (l) Temperature. The optimum temperature for the development and infection of pathogens is 24-28°C, which is significantly affected if they are higher than 30°C or lower than 18°C. (2) pH. The pH of 4.5-5.8 is most suitable for the germ development. That is to say, Fusarium oxysporum is suitable for use in acidic soils, and is not suitable for growth, development, and infestation in alkaline soils. (3) Soil aeration. Loose soil, good ventilation, light incidence; soil viscosity, poor ventilation, heavy disease. In addition, there is a significant difference in disease resistance among varieties, and the dead plant rate of susceptible varieties and disease-resistant varieties can be more than doubled. The strength of the same species has a significant effect on the degree of disease. According to our experiments, 8 were selected. Different species of "Changchun Mici" varieties, inoculation test, the dead plant rate can be more than doubled. (II) Micro-pollution and pollution-free prevention and control techniques 1. Select traditional varieties of disease-resistant varieties, such as Changchun Mimi, Beijing Spur, and Yeer III. The recent successful resistance to disease has surpassed that of Changchun Mimi. Shandong's 87-l, 87-1-2, Heilongjiang's Longzao 3, Beijing's Zhongnong 5, Guangdong's Xiaqing 4, etc. 2. Note that it is best to rotate crops with non-melon crops for 5-6 years. At least 3 years apart. In areas where rice is grown conditionally, one-year rotation with rice has obvious effects. 3. Change the pH value of the soil in heavily replanted areas or heavily replanted plots. Combine pre-planting soil preparation with 80-100 kg of hot lime powder per acre to change soil pH. 4. Vertebral grafting disease prevention measures cucumber is a shallow root crop, poor disease resistance, pumpkin can be used as a method of stocking, grafting before seedlings, survival after planting, the disease can be significantly reduced, with melons as rootstock also has good results. The greenhouse growers are particularly suitable. 5. Pharmaceutics control serious disease plots, according to medicine, soil ratio before planting 1: 100, use thiophanate-methyl, carbendazim and other pesticides into a uniform drug into the planting ditch, according to 100 kg per mu of soil. According to another Gansu Provincial Plant Protection Station in 1988, it was treated with 48% aqueous solution of Rhizobia 800 times, and the final control effect was 81.49%. Hebei Rongcheng Plant Protection Company soaked seeds with watermelon 2000 times for 6-8 hours. After washing, the average control effect reached 88.4%. 6. High temperature treatment of soil cover film Given that the heat-resistance limit of Fusarium oxysporum is 34-36°C, it can be used to cover severely affected land with pre-covered mulching film and strong sun drying (3-5 days of sun exposure, 3-5 days after sweeping the surface soil and then 3-5 days The way to deal with the topsoil.

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