Cultivating strong and prosperous rice is the basis for high yield of rice. However, due to the large temperature changes in early spring in high-cold areas of northern China, rice seedlings are vulnerable to cold wave infestation, causing various physiological diseases of rice and affecting seedling raising. Physiological diseases in rice seedlings during cold winter are mainly caused by low temperature. This paper briefly introduces the common physiological disease symptoms, causes and preventive measures at rice seedling stage in northern cold regions.
1 Main types of physiological diseases in rice seedlings
1.1 Rotten buds
a. Main symptoms The seeds have not germinated or have just germinated, the color of the chaff has deepened, and the grain has become stiff or has long decayed.
b. Occurrence of seed damage or seeding too deep, seedbed too wet.
1.2 Heigen
a. The main symptoms of the root blackened and rot, no new roots, yellow or black buds.
b. Causes Excessive amount of organic fertilizer, excessive moisture in the seedbed, excessive temperature, hydrogen sulfide gas generation, and bud seedling poisoning.
1.3 Cotton rot
a. The main symptoms of the bud around the dense cotton white mold or disc rust brown or stained green soft block, bud tip fade, bending and withered.
b. Causes of low temperature, weak seedling resistance, invasion of cotton rot bacteria.
1.4 Scrub
a. Main symptoms This is the most common and most harmful physiological disease of dry seedlings in paddy fields in cold regions. It is also called dry and dry type. The young part of the heart and leaves lost water first, withered and curled up, and then expanded to the whole plant. When it died, the leaves were green, yellow, or slightly yellowish and dead. The waiting point for bacterial wilt is the dead root after the first dead leaves, and the seedlings die quickly.
b. The cause of the occurrence of strong cold air, the temperature dropped sharply. During the day, it was sunny and dry. The temperature dropped sharply at night (below 5°C). Frost often appeared in the morning and the weather was dry and cold. The temperature difference between day and night was great. In this kind of weather, if the cold work is not done well, it will be blue and dry. Seedlings are chilled by low temperature or suddenly turned cloudy after long-term rain, rapid increase in temperature, rapid increase in leaf temperature, rapid transpiration rate, slow rise in ground temperature, low rhizosphere temperature, slow water absorption rate, lack of water supply for transpiration, and imbalanced water balance The seedlings lose water and die. The greater the temperature change, the greater the temperature difference, the more severe the bacterial wilt.
1.5 yellow dry
a. The main symptoms This is also a relatively common and harmful physiological disease in rice breeding in cold regions. It is also called wet and cold type. The leaves turn yellow and die from the outside to the inside and from the bottom up. After the first dead leaves, the death rate is slow.
b. Causes The low temperature and long duration of rain continued, the photosynthesis of the seedlings was very weak or even stopped, and the roots' ability to absorb nutrients was inhibited. Therefore, less synthetic matter was produced, while breathing was significantly increased and organic matter was consumed in large quantities. The energy released by the seedlings after being chilled and damaged by cold injury is converted into heat energy. The internal energy not only does not accumulate, but it is consumed in large amounts. Therefore, the dry matter of the seedlings gradually decreases, and even the yellow crops die.
2 Preventive measures
Physiological diseases during rice seedling stage in northern high-cold areas are mainly caused by low temperature, weakening of seedlings' life activities, loss of water balance, and other reasons. Therefore, the key to preventing physiological diseases is to do a good job in the management of Putian and cultivate strong seedlings.
a. Select seeds. Selecting seeds full of seeds, strong vitality, and no spots can effectively prevent or reduce rotten buds and rotten rots.
b. Fine bed. Flat bed surface, loose bed soil, increase the application of organic fertilizer, so that the mu bed ventilation, seedling roots grow robust, strong vitality, and enhance cold resistance.
c. Reasonable fertilization. It is necessary to meet the needs of seedling growth for nutrients, but also to prevent excessive fertilization. If the nutrient is insufficient, the seedlings will grow thin and the cold tolerance will be greatly reduced. However, if too much fertilizer is applied, especially if the previous nitrogen fertilizer is excessive, the growth of the seedlings will be luxuriant, the bones will be soft and the cold resistance will be reduced. Therefore, in the early stage, less nitrogen fertilizer should be applied, and decomposed organic fertilizer and phosphorus and potassium fertilizers should be added. If the shallow layer is not suitable for more fertilizer, the Zanthoxylum Bunge or other nursery fertilizer should be evenly mixed into the 10 cm deep soil layer. The agent or fertilizer is sprinkled on the surface of the bed soil, which can not only avoid the excessive fertilizer in the early stage, cause the seedlings to form weak seedlings, but also ensure the demand of nutrients in the later period of the root system, promote the development of the root system of the seedlings, and improve the cold resistance.
d. Improve the quality of sowing. Cover soil should not be too thick, with 1 ~ 2 cm is appropriate.
e. Do a good job of cold insulation. Especially in the three-leaf stage of rice, the cold resistance is the worst. Therefore, we must pay attention to the changes in the weather during this period, and do a good job of protecting the seedlings before the onset of the cold wave. Grass cover can be used to cover or protect the seedlings with water, because the water temperature is slightly higher than the temperature of the surface soil during the cold wave, and the water layer can protect the roots from the cold wind.
f. Pay attention to air conditioning and master the ventilation technology. To open the film before the advent of high temperatures, with the increase of temperature, ventilation from small to large, suddenly avoid sudden increase in the wind at noon high temperature, so that seedbed temperature changes drastically, resulting in water imbalance seedlings and cause bacterial wilt. Ventilation starts from the leeward side and gradually expands the ventilation openings. Do not open the ventilation openings on the windward side first so that the seedlings do not suddenly hit the cold wind.
g. Grasp the seedbed management after cold damage. If the weather suddenly turns cloudy after the seedlings are chilled and the temperature rises quickly, adjust the temperature inside the seedbed. If the temperature in the seedbed rises too fast, the evapotranspiration suddenly increases and the root vitality has not been restored. The water absorption capacity is poor and the water supply cannot be transpired. This can lead to imbalance of water balance and the seedlings lose water too quickly and cause blue and dry. Grass cover can be used to allow a small amount of sunlight to enter the nursery shed, so that the seedbed temperature slowly rises, the seedlings slowly recover, and gradually remove the straw curtain, which can reduce the incidence of bacterial wilt.
h. Apply soil bactericide. Low temperature weakens the viability and resistance to disease of the seedlings. The germs will take advantage of it and invade the roots of the roots, killing the seedlings. The rice bran-strengthening agents commonly used in production contain soil bactericides. If the quality stimulant products are selected and properly used, soil-borne diseases can be effectively prevented.
In short, the prevention of physiological diseases and the cultivation of brawn are complementary to each other. Effective prevention of physiological diseases is conducive to the development of strong and prosperous, and the development of strong and powerful can enhance the ability to resist physiological diseases. To strengthen the seedbed management, regulate the relationship between water, fertilizer, gas, and heat, we will be able to grow strong seedlings and lay a good foundation for the high yield and yield of rice. (020)
(Institute of Crop Nutrition Practical Technology, Heilongjiang Academy of Agricultural Sciences, Harbin 150086)
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