Control techniques of Maize head Smut

Corn head smut, also known as black rice and dumb corn, is common in North, Northeast, Central, Southwest, South and Northwest China. Since the disease was first reported in Northeast China in 1919, it has spread rapidly and occurred to varying degrees every year. From the point of view of China, the disease is more serious in the northern spring corn area, the southwest hilly and mountainous region and the northwest corn area. The incidence rate is 2%-8% in general years, and 60%-70% in individual plots, resulting in heavy losses. Maize head smut has been basically controlled in the 1980s, but it is still one of the main diseases in maize production.

Harmful symptoms of maize head smut

The typical symptom of maize head smut is the deformation of male flower organ, the base of male flower is enlarged and the inside is a bag of black powder, which can not form male ear. The female ear became shorter and the base was thick. except for the bracts, the whole ear was a packet of black powder and scattered filaments, which seriously affected the yield of corn.

1. Seedling symptoms of maize head smut.

Maize head smut is a systematic infectious disease at seedling stage. It generally shows typical symptoms at panicle stage, which mainly harms female and male spikes. The severely damaged plants can show a variety of symptoms at the seedling stage. The tillers of the seedlings increased in tufted shape, the plants were obviously dwarfed, the internodes were shortened, and the leaves were dark green and straight. Farmers said that the disease was short, dense leaves, thick at the bottom, thin at the top, dark leaves, green in color, and curved in the body. In some varieties, yellow-white stripes parallel to the veins appeared on the leaves, and the heart leaves of some seedlings curled tightly together in a whip-like shape.

2. Symptoms of maize head smut at adult stage.

The symptoms on the diseased ear in the adult stage of maize can be divided into two types: black ear and abnormal ear.

① smut, except bracts, the whole ear becomes a smut bag, which is mixed with filamentous host vascular bundle tissue, so it is called head smut. The damaged ear is short, the base is thick, the tip is pointed, nearly spherical, does not spit filaments.

② abnormal spike, is due to male spike floral organ deformation and does not form stamens, its glume is leafy due to bacterial stimulation; female panicle glume may also be excessively grown into tubular long thorns due to bacterial stimulation, showing a hedgehog head shape, the base of the long thorn is slightly thicker, the tip is slightly thinner, the central empty pine, the length is different, clustered upward from the base of the ear, the whole ear is deformed.

Transmission route of maize head smut

The pathogen of maize head smut is spore heap smut, which overwinters mainly as winter spores in the soil, and some are mixed with manure or adhere to the seed surface. Soil carrying bacteria is the main source of primary infection, while seed carrying bacteria is the main way of long-distance transmission of the disease. Teliospores can survive in soil for 2-3 years. Teliospores begin to mature at the silking stage of the female ear of maize, and a large number of them fall into the soil, and some of them fall on the seeds (especially at the harvest stage). After sowing, the germ is usually infected when the seeds germinate or the seedlings are unearthed, and some also occur at the 2-leaf 3-leaf stage (it is reported that the final stage of infection is 7-8-leaf stage). Teliospores germinate to produce separated basidiospores, and basidiospores germinate to produce infectious filaments, which invade from the germ or radicle, and quickly expand to the stem and grow along the growing point. When the flower bud begins to differentiate, the hyphae enter the primitive body of the floral organ, invade the female and male spikes, and finally destroy the male and female flowers. Because the growth cone of maize grows faster and the mycelium expands slowly, it fails to enter the stem growth point of the plant, which results in the phenomenon that some diseased plants only occur in the female ear but not in the male ear.

The pathogen overwintered on soil, manure or seeds and became the source of infection at the beginning of the next year. Seed carrier is the main way of long-distance transmission. Chlamydospores live in the soil for 2-3 years. Invasion in seedling stage is a systematic infection disease. When corn sprouts after sowing, the overwintering chlamydospores also begin to germinate, which can invade from the white tip stage to the 4-leaf stage and reach the growth point. With the growth and development of maize plants, they enter the flower buds and ears, form a large number of black powder and become silk black spikes. Produce a large number of winter spores to survive the winter. Corn continuous cropping for a long time and early sowing corn is more serious, and alpine and cold land is easy to occur. The disease in sandy soil is mild. The incidence of good soil moisture in dry land is light, while that of poor soil moisture is serious.

Conditions for the occurrence of head smut in maize

1. The planting of a large number of susceptible varieties is one of the factors leading to the serious occurrence of head smut. In addition, new physiological races may appear in pathogens, resulting in the loss of resistance of the original disease-resistant varieties.

2. Long-term continuous cropping led to a rapid increase in soil bacterial content. It is reported that if the number of bacteria is reflected by the rate of diseased plants, the content of bacteria in soil can increase by about 10 times every year.

3. Use uncooked barnyard manure. According to the experiment, the incidence of pig manure was 0.1%, while that of cow dung in ditch was 17.4% and 23%, and that of cow dung was 10.6% and 11.1%.

4. The amount of bacteria in the soil will increase if the seed is not disinfected and the remains of the diseased plant are not properly treated, resulting in the serious occurrence of the disease.

5. The soil temperature and humidity during the period from sowing to emergence of maize are closely related to the disease. The soil temperature in the range of 15-30 ℃ was favorable for bacterial invasion, and 25 ℃ was the most suitable. Too high or too low soil moisture is not conducive to bacterial invasion, and the incidence is the highest under 20% humidity. In addition, the disease is more serious when the altitude is higher, the sowing is too deep and the seed viability is weak. The infection temperature limit was 15: 35 ℃, the suitable infection temperature was 20: 30 ℃, and the optimum infection temperature was 25 ℃. Soil water content less than 12% or more than 29% is disadvantageous to the disease.