Ascochyta blight of chickpea

Ascochyta blight is caused by the fungus Ascochyta rabiei, which belongs to the kingdom Fungi. It is a highly specialized pathogen that specifically affects chickpeas and survives in crop debris and infected seeds.

The life cycle of the pathogen involves the production of pycnidia, which contain numerous pycnidiospores. These spores serve as the primary source of inoculum that spreads the disease during the growing season.

The fungus thrives in cool, moist conditions with temperatures optimal around 15–25°C. Spores are primarily disseminated by rain splashes, wind, and movement of equipment or animals through the field.

Ascochyta rabiei exhibits significant genetic variability, which poses a constant challenge for breeding disease-resistant chickpea cultivars. The pathogen can attack all parts of the plant at any developmental stage.

Identification is primarily based on the visual appearance of necrotized lesions containing tiny, dark, pin-point structures known as pycnidia, which are diagnostic for this fungus.

The pathogen infects all aerial parts of the chickpea plant, including leaves, stems, pods, and seeds. Heavy infection results in rapid defoliation and severe stunting of the entire plant.

Lesions on the stems often cause them to break, leading to lodging of the crop. This not only reduces the potential yield but also interferes with mechanical harvesting operations.

Infection of pods leads to shriveled, deformed, or entirely sterile seeds. Infected seeds act as the primary carrier, spreading the disease to new planting areas in subsequent seasons.

Severe outbreaks can lead to total crop failure. Beyond yield loss, the quality of harvested grains is compromised, often rendering the crop unsuitable for commercial use.

Secondary infections occur rapidly in conducive weather, causing further rotting of plant tissues and potentially destroying vast areas of the field within a short timeframe.

Early symptoms appear as small, circular or oval spots on leaves, characterized by a light center surrounded by a dark brown margin. Over time, these spots coalesce into larger, irregular necrotic areas.

Stem lesions are elongated and brown, often leading to girdling of the stem. This weakens the structural integrity of the plant, frequently resulting in breakage at the site of infection.

Pod symptoms appear as circular, sunken brown lesions. If the infection reaches the seeds within, they develop dark, necrotic blotches, which significantly reduce seed germination rates.

During periods of high humidity, the centers of the lesions produce a white to greyish mass of spores, which can be easily observed under microscopic examination or with a hand lens.

Infected seedlings may die shortly after emergence if the seeds were contaminated. This leads to poor stand establishment and uneven growth patterns throughout the field.

The primary control measure is the use of disease-free, certified seed. Treating seeds with effective fungicides is essential to eliminate internal and external inoculum before planting.

Implementing a rigorous crop rotation schedule (at least 3–4 years without chickpeas) is crucial for reducing the amount of soil-borne inoculum and breaking the pathogen's life cycle.

Spatial isolation of new fields from previous chickpea areas prevents long-distance spore dispersal. Deep plowing of crop residues helps accelerate the decomposition of infected debris.

Fungicide application during the growing season is necessary when environmental conditions favor disease development. Preventive measures are more effective than reactive treatments.

• Selection of resistant or tolerant chickpea cultivars.
• Use of high-quality fungicide-treated seeds.
• Proper field hygiene and management of crop residues.
• Scouting for early symptoms to optimize fungicide timing.