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Wheat and Pulses crops diseases | Diseases of Field & Horticultural Crops & Their Management-II

Some Basic Concepts

Greek word: Pathas suffering. Logus = study

Plant pathology is the study of plants and their management. Causes of suffering

→ Father of plant pathology - Anton de Bary

Etiology refers to the study of the causes of a disease, which may include factors related to the host, pathogen, and environment that interact to produce the disease.

A disease is a condition that disrupts normal bodily function and is typically characterized by the presence of symptoms resulting from continuous irritation or damage.

Disease Cycle:

• Inoculation: The pathogen comes into contact with the host plant and infects it.
• Incubation: The pathogen starts to grow and reproduce inside the host plant.
• Infection: The pathogen causes damage to the plant's tissues, leading to the development of disease symptoms.
• Dispersal: The pathogen produces spores or other structures that allow it to spread to other plants and infect them.

Symptoms:- Symptoms are the observable or internal changes in the host that occur as a result of a disease or injury. These changes can include physical signs, such as a rash or fever, and changes in behaviour or physiological processes.

Wheat Crops

Wheat Rusts:

Symptoms:

• Appearance of reddish-brown or yellowish-brown pustules on leaves, stems, and grains.
• These pustules can rupture, releasing powdery rust spores that can easily be rubbed off with a finger.
• Severely infected leaves can turn yellow, wither, and die, reducing photosynthesis and affecting yield.
• Three types of Rusts:
• Stem rust: elongated reddish-brown pustules on stems and leaves.
• Leaf rust: small, roundish pustules causing yellowish appearance on leaves.
• Stripe rust: yellow stripes of pustules on leaves.

Etiology:

• Caused by fungal pathogens of the genus Puccinia.
• Stem rust: Puccinia graminis f. sp. tritici.
• Leaf rust: Puccinia triticina.
• Stripe rust: Puccinia striiformis.

Disease Cycle:

• Rust pathogens survive on alternate hosts or as dormant spores on crop debris.
• Urediniospores (spores) are produced on infected plants.
• When environmental conditions are conducive, spores (urediniospores) are produced on infected plants and spread by wind to infect healthy plants.
• Infection occurs when spores land on susceptible plant tissues and germinate.

Management:

• Cultural Practices:
  • Resistant Varieties: Plant rust-resistant wheat cultivars or hybrids that are less susceptible to rust infections.
  • Timely Sowing: Opt for timely sowing to avoid the peak period of rust infection.
  • Avoid Continuous Cropping: Practicing crop rotation with non-host crops helps break the disease cycle.
• Sanitation Measures:
  • Crop Residue Removal: Clear the field of infected crop residues after harvest to reduce the source of inoculum.
  • Weed Control: Control weeds that can serve as alternate hosts for rust pathogens.
• Chemical Control:
  • Fungicides: Application of appropriate fungicides can effectively manage rust infections, especially during high disease pressure periods.
  • Application Timing: Apply fungicides preventively or as soon as rust symptoms are observed.
• Integrated Disease Management:
  • Resistant Varieties + Fungicides: Utilize both rust-resistant varieties and fungicides for a more comprehensive approach.
  • Monitoring: Regularly scout the crop to detect early rust symptoms for timely intervention.
• Early Sowing: Early sowing can reduce disease severity by escaping the period of high rust incidence.
• Crop Rotation: Rotate wheat with non-host crops to break the disease cycle.
• Farm Hygiene: Ensure farm equipment used in rust-infested fields is properly cleaned before moving to uninfested fields.

Wheat Loose Smut:

Symptoms:

• Inflorescence Transformation: Loose smut primarily affects the wheat inflorescence (flowering part). Infected heads are replaced by masses of dark brown, powdery spores (smut balls) that contain fungal spores.
• Smuts at Maturity: At maturity, smut balls disintegrate, releasing large quantities of spores that can infect healthy plants.

Etiology:

• Pathogen: Loose smut is caused by the fungus Ustilago tritici.
• Infection and Transmission: The fungus overwinters in infected seeds (smut balls). These infected seeds, when sown, result in the growth of infected plants.

Disease Cycle:

1. Seed Contamination: Infected seeds (smut balls) are sown in the field.
2. Systemic Infection: The fungus penetrates young seedlings as they germinate and grows systemically within the plant.
3. Smut Ball Formation: During flowering, the fungus replaces the wheat head with smut balls.
4. Spore Dispersal: At maturity, smut balls rupture, releasing vast numbers of spores.
5. Infection of Healthy Plants: Spores land on healthy plants, germinate, and penetrate through the stomata, starting the infection cycle anew.

Management:

• Use Certified Seed: Use certified, disease-free seed to avoid introducing smut into the field.
• Seed Treatment: Treat seeds with fungicides to reduce the risk of infection. Fungicides like Thiram, Captan, Carbendazim etc.
• Hot Water Treatment: Immersion of seeds in hot water (52°C for 15 minutes) can help eliminate smut spores from the seed surface.
• Crop Rotation: Rotate wheat with non-host crops to reduce inoculum buildup in the field.
• Eradication of Volunteer Plants: Remove volunteer wheat plants that may serve as a source of infection.
• Resistant Varieties: Plant resistant wheat varieties to reduce the risk of smut infection.
• Systematic Survey: Regularly monitor the crop for smut symptoms and take necessary measures if detected.

Karnal bunt

Symptoms:

• External Symptoms: The most noticeable symptom is the presence of black masses of spores (smutted bunt balls) that replace kernels in the wheat spikelet.
• Internal Symptoms: Infected kernels are partially or completely replaced by spores, resulting in a smutty odor and discolored flour.

Etiology:

• Pathogen: Karnal bunt is caused by the fungus Tilletia indica.
• Infection and Transmission: The fungus survives in the soil as teliospores, which can infect young wheat plants during germination.

Disease Cycle:

1. Soil Contamination: Teliospores in the soil are the primary source of inoculum.
2. Seedling Infection: The fungus infects the seedling as it germinates and establishes itself systemically within the plant.
3. Systemic Growth: The fungus remains latent in the plant until the reproductive stage.
4. Bunt Ball Formation: Infected kernels are replaced by bunt balls filled with dark brown spores.
5. Spore Dispersal: Ruptured bunt balls release spores into the environment.
6. Infection of Healthy Plants: Spores infect healthy plants, and the cycle continues.

Management:

• Use Certified Seed: Plant certified, disease-free seed to prevent introducing the pathogen into the field.
• Seed Treatment: Apply fungicidal seed treatment to protect germinating seedlings.
• Crop Rotation: Avoid planting wheat in consecutive seasons in contaminated fields.
• Early Sowing: Early sowing can help escape the period of high disease pressure.
• Resistant Varieties: Planting resistant wheat varieties is an effective way to manage the disease.
• Sanitation: Remove and destroy volunteer wheat plants to reduce inoculum sources.
• Quarantine Measures: Ensure that seed and machinery are not contaminated with bunt spores.
• Hot Water Treatment: Infected seeds can be treated with hot water (52°C for 15 minutes) to kill the bunt spores.

Powdery Mildew:

Symptoms:

• White Powdery Growth: Powdery mildew appears as white, powdery fungal growth on the leaves, stems, and heads of wheat plants.
• Chlorosis: Infected leaves may show yellowing (chlorosis) due to reduced photosynthesis.
• Stunted Growth: Severe infections can lead to stunted growth and reduced grain yield.

Etiology:

• Pathogen: Wheat powdery mildew is caused by several species of the fungal genus Blumeria (formerly Erysiphe).

Disease Cycle:

1. Overwintering Structures: The fungus overwinters as dormant structures in crop residues.
2. Initial Infection: In spring, spores (conidia) are produced on infected residues and are wind-dispersed to new growth.
3. Infection and Colonization: Conidia land on wheat leaves, germinate, and produce specialized structures called appressoria to penetrate the leaf surface.
4. Fungal Growth: The fungus grows within the leaf, forming a powdery mycelium.
5. Spore Production: As the mycelium matures, it produces more conidia that spread to other parts of the plant and neighboring plants.

Management:

• Resistant Varieties: Planting resistant wheat varieties can significantly reduce disease severity.
• Timely Planting: Early planting can help avoid peak disease pressure.
• Fungicides: If the disease risk is high, timely application of fungicides can suppress powdery mildew.
• Cultural Practices: Adequate spacing between plants, good air circulation, and proper irrigation can reduce humidity levels that favor disease development.
• Crop Rotation: Rotate wheat with non-host crops to reduce the carryover of inoculum.
• Sanitation: Remove and destroy crop residues after harvest to eliminate overwintering structures.
• Monitoring: Regular scouting for disease symptoms can help determine the need for fungicide application.

Ear cockle

Symptoms:

• Swollen Kernels: Infected wheat spikes develop swollen and distorted kernels instead of normal grains.
• White to Pink Color: Infected kernels are often white or pinkish in color and lack the typical grain structure.
• Reduced Quality: The presence of ear cockle reduces the overall quality and market value of wheat.

Etiology:

• Pathogen: Wheat ear cockle is caused by the fungus Anguina tritici, which is a seed-borne pathogen.

Disease Cycle:

1. Infested Seeds: The fungus survives within the seeds of the wheat plant.
2. Infection of Floral Organs: During flowering, the fungus infects the floral organs of the wheat plant.
3. Nematode Transmission: The fungus is vectored by a nematode (parasitic worms found in plants) called the wheat seed gall nematode (Anguina tritici), which feeds on the infected floral parts.
4. Gall Formation: The nematode feeding causes the development of galls within the floral organs, leading to the characteristic swollen kernels.
5. Propagation: Infected seeds with swollen kernels produce nematode-infested seeds that continue the disease cycle.

Management:

• Use Certified Seed: Plant certified disease-free seeds to avoid introducing infected material into the field.
• Crop Rotation: Rotate wheat with non-host crops to reduce the nematode population in the soil.
• Early Planting: Plant wheat early to avoid peak nematode activity and reduce the chances of infection.
• Nematicides: Soil-applied nematicides may help reduce nematode populations, but their efficacy can vary.
• Sanitation: Remove and destroy infected plant residues after harvest to minimize the carryover of nematodes.
• Resistant Varieties: Some wheat varieties have shown resistance to the nematode vector; planting these can reduce the disease's impact.
• Monitoring: Regular field monitoring and scouting can help identify the presence of swollen kernels and take appropriate action.

Gram:

Wilt

Symptoms:

• Wilting and Yellowing: Infected gram plants exhibit wilting and yellowing of leaves, starting from the lower leaves.
• Leaf Drop: Infected leaves may drop prematurely.
• Stunted Growth: Plants infected at an early stage may show stunted growth.
• Brown Vascular Tissues: The vascular tissues of infected plants turn brown due to the pathogen's invasion.

Etiology:

• Pathogen: Gram wilt is caused by the soil-borne fungus Fusarium oxysporum f. sp. ciceri.

Disease Cycle:

1. Soil Infestation: The pathogen persists in the soil as chlamydospores and mycelium.
2. Root Infection: The pathogen infects the root system of gram plants through wounds or natural openings.
3. Vascular Invasion: Once inside the plant, the pathogen invades the vascular tissues, causing blockage and disruption of water and nutrient transport.
4. Wilting and Yellowing: As the vascular tissues are affected, the plant experiences wilting and yellowing symptoms.
5. Spread: The pathogen spreads through infected soil, contaminated tools, and infected plant debris.

Management:

• Resistant Varieties: Plant resistant or tolerant gram varieties that have shown reduced susceptibility to wilt.
• Crop Rotation: Practice crop rotation with non-host plants to reduce pathogen populations in the soil.
• Sanitation: Remove and destroy infected plant residues to minimize the source of inoculum.
• Seed Treatment: Treat seeds with fungicides before planting to reduce the chances of initial infection.
• Soil Treatments: Application of soil fungicides can help reduce soilborne pathogen populations.
• Proper Irrigation: Avoid excessive moisture, as wet conditions can favor the pathogen's spread.
• Avoid Infected Soil: Avoid planting in fields with a history of gram wilt to prevent disease recurrence.

Ascochyta blight

Symptoms:

• Lesions on Leaves: Infected leaves develop small, circular lesions with dark centers and reddish-brown margins.
• Necrotic Spots: Lesions coalesce, leading to large necrotic spots on leaves.
• Leaf Drop: Severe infections can cause defoliation, leading to reduced photosynthesis.
• Pod Infection: Pods may also be infected, showing circular, dark lesions with raised centers.

Etiology:

• Pathogen: Ascochyta blight is caused by the fungus Ascochyta rabiei.

Disease Cycle:

1. Survival: The pathogen overwinters in infected plant debris and seeds.
2. Spore Production: In spring, conidia (spores) are produced on infected debris.
3. Spread: Conidia are wind-dispersed and can infect leaves through stomata.
4. Infection: Conidia germinate on leaves, forming appressoria and penetrating through stomata.
5. Lesion Development: The fungus grows within the leaf tissues, causing lesions.
6. Secondary Spores: New conidia are produced on lesions, and rain or wind can splash or disperse them.
7. Pod Infection: Conidia can also infect pods, causing lesions and reducing seed quality.

Management:

• Resistant Varieties: Plant resistant or tolerant varieties that have shown reduced susceptibility to Ascochyta blight.
• Crop Rotation: Practice crop rotation with non-host plants to reduce pathogen populations in the soil.
• Seed Treatment: Treat seeds with fungicides before planting to reduce the chances of initial infection.
• Sanitation: Remove and destroy infected plant residues to minimize the source of inoculum.
• Foliar Fungicides: Application of fungicides can help manage disease during the growing season.
• Proper Plant Spacing: Maintain proper plant spacing to promote air circulation and reduce humidity.
• Early Planting: Planting early can help escape disease pressure in some regions.