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

Diseases of Field & Horticultural Crops & Their Management-II 3(2+1)

Unit-I

Syllabus
Wheat and pulses crops: Symptoms, etiology, disease cycle and Management of the following diseases:

Wheat: Rusts, Loose smut, Karnal bunt, Powdery mildew, and Ear cockle; 
Gram: wilt, and Ascochyta blight; 
Lentil: rust

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.

Lentil

Rust

Symptoms:

• Yellow to Orange Pustules: Rust-infected lentil plants develop yellow to orange pustules on the lower leaf surface.
• Spore Release: The pustules rupture, releasing powdery spores that can rub off on fingers.
• Lesions on Pods: Pustules may also appear on pods, causing discoloration and reduced seed quality.

Etiology:

• Pathogen: Rust in lentil is caused by the fungus Uromyces viciae-fabae.

Disease Cycle:

1. Survival: The fungus overwinters on infected plant debris.
2. Spore Production: In spring, uredinia (rust pustules) develop on leaves and pods, producing urediniospores.
3. Spore Dispersal: Urediniospores are wind-dispersed and can travel long distances.
4. Infection: Spores germinate on wet leaves, forming infection structures and penetrating through stomata.
5. Lesion Development: The fungus grows within leaf tissues, causing pustules to develop.
6. Secondary Spores: New urediniospores are produced on pustules, continuing the disease cycle.

Management:

• Resistant Varieties: Plant lentil varieties that are resistant to rust to reduce disease impact.
• Crop Rotation: Rotate lentil with non-host crops to reduce pathogen buildup in the soil.
• Sanitation: Remove and destroy infected plant residues to reduce overwintering inoculum.
• Foliar Fungicides: Application of fungicides can help manage disease during periods of high infection risk.
• Timely Planting: Plant lentil at the appropriate time to avoid peak disease conditions.
• Monitoring: Regularly monitor fields for early signs of rust and take action if necessary.

Integrated disease management practices, including the use of resistant varieties, proper planting practices, and fungicides, can help control rust in lentil and minimize its impact on yield and quality.