What are the causes of rice bakanae disease?
Rice bakanae disease is a major disease in the rice cultivation process. When this disease appears, it can often cause a 10-20% reduction in rice yield, and in severe cases can cut the yield in half, so finding the causes and doing a good job of prevention brooks no delay. What are the causes of rice bakanae disease? How is it prevented and controlled?
I. What is rice bakanae disease
Rice bakanae disease, also known as leggy disease and white stalk disease, is a fungal disease. It can occur from the seedling stage to the heading stage of rice, with peak symptom expression appearing at the seedling stage, main field stage and heading stage. Rice is most susceptible to the disease at the seedling stage.
Because of poor root development, diseased seedlings grow slender and weak, the whole plant is pale yellow-green, and it stands nearly 1/3 taller than healthy plants, with narrower leaves. Most diseased plants die before transplanting, and a small number of diseased plants die within 25 days after transplanting. When air humidity is high, a pale red or white mold-like substance, namely the conidia of the pathogen, is sometimes produced on the near-ground part of dead seedlings. The degree of disease occurrence at the rice seedling stage is related to seed-borne bacteria.
II. Causes of rice bakanae disease
1. The most important primary infection source of rice bakanae disease is infected seeds, followed by diseased rice straw. After the seeds germinate, the pathogen invades from the coleoptile, roots and root crown of the seedlings or through wounds. Plant wounds favor pathogen invasion and cause diseased seedlings to grow leggy; after diseased seedlings are transplanted, they cause rice seedlings to develop the disease; at the same time, the conidia produced by diseased plants can carry out secondary infection with the help of airflow, causing grains and rice straw to carry the pathogen, forming a cycle of infection and harming rice.
2. High temperature creates conditions for the occurrence of rice bakanae disease. The pathogen of this disease likes high temperature, and high temperature is extremely favorable for the reproduction, infection and occurrence of the rice bakanae disease pathogen. When the soil temperature is 30-35°C, diseased seedlings appear the most; at 25°C, fewer diseased seedlings appear. When seeds and seedlings have wounds, it is favorable for pathogen invasion.
3. Under the same conditions, the seed-borne bacteria rate is extremely high, and the difference in disease occurrence among varieties is obvious. Japonica rice is significantly more severely affected than indica rice, and the average diseased plant rate of different varieties is between 0.07%-2.8%.
4. The pathogen of rice bakanae disease belongs to the Ascomycetes. On the one hand, during seed soaking before sowing, the conidia on infected seeds contaminate disease-free seeds and cause infection; on the other hand, the degree of mechanization of rice harvesting is extremely high, and while the technology of returning straw to the field improves soil fertility, it also increases the accumulation of pathogens on diseased residues in the field and on seeds.
5. The occurrence of bakanae disease in dry-raised seedlings is more severe than in water-raised seedlings.
6. Improper seeding is caused by not operating in accordance with technical specifications. Insufficient seed soaking concentration will affect the effectiveness of the pesticide, and the result can only be an increase in the occurrence of bakanae disease in the main field.
III. How to prevent and control rice bakanae disease
1. First, establish disease-free seed fields, select and plant disease-resistant varieties, and when retaining seeds, select and breed healthy, disease-free seeds and remove injured and blighted seeds. This is the most effective and reliable method. Second, doing a good job of seed disinfection treatment is the key to disease prevention. Before disinfection treatment, rice seeds should be sun-dried on sunny days for 1-3 days, then soaked with 300-fold dilution of 80% strong chlorine essence. The control effect can reach 98%. Soak late rice for 12 hours, early rice for 24 hours, then soak in clean water. Soak seeds with clarified liquid of 3% quicklime water; at 25°C, soaking for 2 days is required, avoiding direct light. The liquid surface should be 10-15cm above the seeds to help the seeds absorb the liquid, and the liquid surface should be kept still. It must not be stirred midway, so as to ensure the pathogen is suffocated.
2. Before sowing, sprouting should not be too long, otherwise the plants are easily injured when sown, which favors pathogen invasion; when transplanting and pulling up seedlings, damage to seedling roots should be avoided as much as possible to prevent poor root development, so as to reduce the chance of bakanae disease occurrence; when transplanting rice seedlings, avoid high-temperature weather and noon, and do not transplant seedlings under the scorching sun, as high temperature is the most suitable condition for the occurrence of bakanae disease.
3. Once infected plants are found, they should be pulled out in time. Diseased plants stand 1/3 taller than normal seedlings and are easy to identify. After pulling them out, burn them in a centralized manner to avoid pathogen spread and reinfection.
4. After harvest, diseased rice straw can be used as fuel or composted at high temperature.
By understanding the causes and conditions of this disease and carrying out relevant prevention and control measures, the disease incidence can be greatly reduced.