Whole wheat rot disease affects both seedlings and mature plants, with symptoms becoming most evident as the plant approaches maturity. During the seedling stage, the pathogen primarily invades the root and lower stem of the seed, causing blackening and rotting. Secondary roots may also be affected. Infected seedlings show yellowing leaves, leaf curling, reduced tillering, and stunted growth, often leading to death in severe cases. The plants appear delayed, sparse, and have darker roots.
After the jointing stage, dark brown hyphae can form on the base of the first or second stem under wet conditions, a condition known as "black foot." This is a key symptom that distinguishes whole wheat rot from other root rot diseases. Severely infected plants exhibit dwarfing, though this may not be as noticeable in later stages. Due to damage at the stem base, the plant may develop "white spikes." In the field, diseased plants often cluster or appear in patches, and in extreme cases, entire plants may die.
The occurrence of the disease follows specific patterns. Mycelia present in crop debris in the soil during summer or winter serve as primary infection sources for the following year. Diseased plant remains in uncomposted organic fertilizers can also act as initial infection sources. Pathogens surviving on wheat seedlings, weeds, or other crops can infect subsequent crops. These primary sources significantly influence the spread of the disease. While ascospores can germinate and cause infections, their impact is far less significant compared to the mycelium in infected plant material. The pathogens are soil-borne and their survival time in the soil varies between 1–2 years to 3–5 years, depending on environmental conditions. Crop rotation is an effective way to reduce disease incidence.
The disease spreads through contaminated manure, irrigation, and farming equipment. There has been debate over whether seeds can carry the disease. While "seed-borne" transmission exists, the presence of the pathogen in commercial seeds is usually minimal. Disease-free regions typically prohibit the transport of seeds from infected areas.
Several factors influence disease incidence:
1. Farming practices: Continuous cropping of wheat followed by corn and then wheat again promotes pathogen accumulation in the soil, increasing disease pressure. Proper crop rotation can reduce the problem, while improper rotation may not. No-till or reduced tillage helps lower disease levels, and early sowing is generally more favorable than late planting.
2. Nutritional factors: A lack of essential nutrients, particularly nitrogen, can promote disease development. However, the relationship between nutrition and disease is complex. Nitrogen deficiency is often linked to increased disease severity, while nitrogen application can help reduce it. Ammonium nitrogen (NH4-N) may decrease wheat disease but increase barley disease, whereas nitrate nitrogen (NO3-N) can increase infection and reduce yield. Increasing organic matter in the soil through organic fertilizers significantly reduces disease incidence. Phosphorus deficiency or an imbalance between nitrogen and phosphorus can worsen the disease. Applying phosphorus fertilizer improves root development, lowers disease severity, and reduces the occurrence of white spikes.
3. Soil properties and climate: Sandy soils, which retain less moisture and nutrients, are more prone to disease. Clay soils tend to be less affected. Alkaline soils favor disease more than acidic or neutral ones. Winter wheat is more susceptible in warm winters, especially when heavy rain occurs in late autumn or early spring. Irrigated fields are more severely affected than dryland. High summer temperatures and rainfall help decompose infected plant material, reducing bacterial populations and lowering disease risk in winter wheat.
4. Variety resistance: Currently, there are no wheat varieties fully resistant to whole wheat rot, either domestically or internationally. Resistance sources in the wheat and barley genera are limited, and differences in disease susceptibility exist among varieties.
To manage the disease effectively, several control measures can be implemented:
1. Crop rotation: In heavily infested areas, proper crop rotation can help control the disease. In sporadic cases, it can delay disease spread. Rotate with non-host crops such as peanuts, tobacco, tomatoes, sugar beets, castor, or green manure for 1–2 years based on local conditions.
2. Balanced fertilization: Increase the use of organic manure to improve soil structure and microbial activity. Apply about 6,000 kg per acre. Inorganic fertilizers should be applied in balanced ratios. Maintain soil available phosphorus above 0.06%, total nitrogen above 0.07%, and organic matter above 1% to slow disease progression. Low levels of these nutrients can lead to higher disease severity.
3. Biological control: In declining wheat fields or those showing signs of disease, planting two consecutive crops of wheat or wheat and corn can help maintain beneficial soil microorganisms that suppress the pathogen.
4. Chemical control: Use 12% triadimenol wettable powder at 0.02–0.03% of seed weight for seed treatment, which provides good disease protection. The 2.5% Siye seed coating agent at a ratio of 1:1000 also offers some control. During the seedling stage, apply 20–30 grams of 12.5% wolfberry fruit or 50% carbendazim per mu in 200 kg of water, and spray along the ridges to treat the stem base.
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