Plant Pathology- ICAR JRF/SRF 2024

• Etiology of Black Mould of Onion: Black mould of onion bulbs in field and storage is caused by the deuteromycetous/ascomycetous fungus Aspergillus niger.
• Symptoms and Characteristics: The fungus produces dense black, powdery crusts of conidia between the dry outer scales and on inner fleshy scales of the onion neck and bulb, causing softening and secondary bacterial rots.
• Other Aspergillus Species:
• Aspergillus flavus: Produces aflatoxins on groundnuts, maize, and stored grains.
• Aspergillus fumigatus: Thermotolerant human opportunistic pathogen.
• Aspergillus nidulans: Model genetic fungus.
• Conclusion: Aspergillus niger is the causal agent of black mould of onion (Option 1).

Correct option: (1) Aspergillus niger

• Epidemiology and Biology of Peach Leaf Curl (Taphrina deformans):
• is true: The fungus overwinters and carries over from season to season as resistant blastoconidia (yeast-like budding conidia) on the bark and dormant bud scales of peach trees.
• is true: Taphrina deformans is an ascomycete that produces naked asci lining the leaf surface, each containing eight primary ascospores that bud into conidia.
• is false: Leaf curl development is favored by cool, wet, rainy weather ($10-15^\circ\text{C}$) during bud break, NOT hot and humid climate.
• is false: Conidia are disseminated by rain splash and wind, NOT by psyllids.
• Conclusion: Features (A) and (C) only are true (Option 3).

Correct option: (3) (A) and (C) only.

• Diseases Caused by Phytophthora citrophthora:
• Citrus Gummosis (Foot Rot / Collar Rot): Caused primarily by Phytophthora citrophthora (and P. nicotianae var. parasitica).
• Symptoms: The pathogen attacks the bark near the soil line, causing water-soaking, brown rotting of the cambium, longitudinal bark cracking, and profuse exudation of dark amber-colored gum (gummosis), girdling the trunk and causing tree decline.
• Other Diseases: Mahali / Koleroga of arecanut is caused by Phytophthora meadii / P. heveae.
• Conclusion: Phytophthora citrophthora causes Gummosis (Option 3).

Correct option: (3) Gummosis

• Integrated Management of Purple Blotch of Onion (Alternaria porri):
• Cultural and Chemical Practices:
• Long crop rotation: Alternaria porri survives on infected crop residues; adopting a 2–3 year crop rotation with non-allium crops deprives the pathogen of host tissues.
• Well-drained field: Dense foliage and standing water promote leaf wetness; good field drainage and optimum spacing lower canopy humidity.
• Seed treatment with Thiram / Mancozeb: Eradicates seed-borne conidia and protects seedlings during emergence.
• Exclusion: Roguing individual plants in large field plantations is impractical against airborne conidia.
• Conclusion: Management involves (A), (C), and (D) only (Option 2).

Correct option: (2) (A), (C) and (D) only.