Control measures of scattered smut of wheat

Wheat loose smut, commonly known as black jaundice, ash bag, etc., is common in many wheat producing areas in China. The general incidence rate is 5%, and the severity can reach more than 10%. In recent years, wheat smut has an increasing trend year by year, especially in the areas where farmers keep their own wheat seeds.

Manifest symptoms

The main damage to ears, stems and leaves can also occur.

The main results are as follows: 1. The ear is damaged to form a bag of black powder, and there is a light gray film on the outside, then the epidermis breaks, the black powder spreads out, and finally a curved ear axis remains. Sometimes there are a few healthy spikelets in the upper part of the ear and turn into black powder in the lower part. In most cases, the main stem and tillers of diseased plants all produce diseased ears, but sometimes some tillers grow normally without being harmed by bacteria.

2. The damage to the stem is not easy to be seen in the field, and the diseased part mostly occurs at the base of the ear axis, and the spores are piled into blister and streak, grayish black.

3. The symptoms of the damage to the leaves are mostly at the base of the leaves, and the symptoms are similar to those in the stem and rarely occur.

After the smut fungus infected wheat, in addition to the typical external symptoms, the internal tissue also changed, which made the cells enlarged, the stomata increased and the number of stomata increased, the mesophyll palisade tissue became compact and the cells became shorter.

Induced pathogen

The pathogen of wheat smut is powdery mildew, the branched hyphae of wheat smut is mononuclear, the colony character is unstable on the culture medium, and the mycelium growth occurs only by the original antecedent mycelium cells. Teliospores are globose to ovoid, light yellow to brown, half of them are dark, half of them are light, and there are micro-thorns on the surface. The size of the spores is 5 Mel 9 μ m, with an average of 6.5 Mel 7 μ m. Teliospores can germinate in both water and nutrient solution. The lowest temperature of germination is 5 ℃, the optimum temperature is 20 min, 25 ℃, and the highest is 35 ℃.

1. Overwintering and spreading

The pathogen of wheat loose smut overwintered in the seed embryo with dormant hyphae, so the only way to overwintering was the seed disease. Winter spores can only survive in the field for a few weeks, and there is no possibility of infection after overwintering.

In the field, the winter spores of the pathogen of wheat scattered black spike are mainly transmitted by the wind and invade the interior through protruding or open stamen glume cracks. In general, teliospores can spread more than 100m away from the disease center, and the farthest guests can spread as far as 1000 meters. The propagation distance is related to the wind speed and the movement of the air flow.

2. Infection

At present, most people believe that the invading filaments of wheat smut pathogen invade directly from the ovary wall. Flowering and pollination are the most suitable periods for pathogen infection. When the teliospore of the pathogen falls on the stigma, style and ovary wall, it can germinate and grow the first hyphae in 24 hours, which invades directly from the epidermis of the ovary wall in the lower part of the ovary or the base of the grain crown, and then invades into the nucellus tissue through the integument, and then enters the base of the grain and lurks in the embryo. This process takes about 18 days. The pathogen can also invade from the back of the grain, from the seed coat, nucellus and powder layer to the scutellum, and then into the meristem of the embryo.

When the seed begins to sprout, the mycelium lurking in the scutellum and growth point invades the first node and the rhizome node of the seedling, and finally enters the ear and other meristems with the growth of the epicotyl.

3. Morbidity condition

The occurrence of wheat loose smut is closely related to the relative humidity during flowering last year. After wheat heading, the field air temperature is often within the suitable temperature range required by bacteria, so humidity becomes the dominant factor. Experiments show that when the relative humidity is 56 Mel 85%, the incidence rate after artificial inoculation is 91%, and under dry conditions (11% relative humidity 11%), the incidence rate is 22%.

The reason for the higher incidence in the following year due to the high humidity during flowering may be that when the relative humidity is high, the glume opening angle is larger, the opening time is longer, and there are more opportunities for bacteria to invade. In addition, under the condition of high humidity, teliospore germinated faster and the germ tube was longer. On the contrary, in the case of drought, teliospore germination is slow and germ tube is short, which is not conducive to the invasion of bacteria.

The breeze is conducive to the spread of spores, foggy or often light rain, conducive to spore germination and invasion. Heavy rain is easy to pour spores into the soil and lose the opportunity of infection, so the incidence of heavy rain in the second year is mild.

Prevention and cure measures

In order to control the loose smut of wheat, in addition to using disease-resistant varieties, the integrated control of planting disease-free seeds and seed treatment should be adopted.

(1) seed treatment

1. Chemical treatment: 50% and Sui'an wettable powder, 25% rust rather wettable powder, 40% mixed seed double wettable powder, seed dressing with 0.2% of the seed amount can achieve good results. The control effect can be improved by mixing the above treated seeds with the coating agent and then mixing the seeds. Some medicaments should be careful not to exceed the prescribed amount when mixing seeds, so as to avoid drug damage.

2. Physical disinfection

(1) soaking seeds in warm soup

Soaking seeds with ① at variable temperature: the seeds were pre-soaked in cold water for 6 hours to germinate the hyphae, soaked in 49 ℃ water for 1 minute, and then immersed in 52 mur54 water for 10 minutes. This method has a good control effect, but it needs to strictly control the temperature, and the operation is complicated, so it is not convenient to popularize and apply it in a large area.

Soak the seeds in ② constant temperature: soak the seeds in 44mur46 ℃ water for 3 hours, then remove them, cool them and dry them. Seed soaking at constant temperature is relatively safe, and has a good control effect, and the incidence can be reduced to less than 0.5%, which is convenient for large area treatment.