पादप रोग विज्ञान

Analysis of plant quarantine legislation:

• 1914: The primary Destructive Insects and Pests Act (DIP Act) was passed in 1914.
• 1947: Independence year, Directorate of Plant Protection, Quarantine and Storage was formed in 1946.
• 1993: Earlier amendment year.
• 2003: The comprehensive 'Plant Quarantine (Regulation of Import into India) Order, 2003' (PQ Order 2003) was notified by the Ministry of Agriculture under the DIP Act 1914 to regulate import of plants and plant materials.

Analysis of viroid characteristics:

• Discovered by Theodor Otto Diener: T.O. Diener discovered viroids in 1971 while studying potato spindle tuber disease.
• Consist of small circular RNA: Made up of short (246–467 nucleotides), single-stranded circular RNA molecules.
• Lack protein coat: Unlike viruses, viroids completely lack any protein coat (capsid).
• All the above statements are correct: Since statements (A), (B), and (C) are all accurate, option (4) is correct.

Analysis of plant parasitic nematodes:

• Heterodera avenae: The Cereal Cyst Nematode (CCN), causal agent of the serious 'Molya disease' affecting wheat and barley crops in light sandy soils of Rajasthan and Punjab.
• Anguina tritici: Wheat seed gall nematode causing ear-cockle disease.
• Globodera pallida: Pale potato cyst nematode attacking solanaceous crops in the Nilgiris.
• Meloidogyne incognita: Root-knot nematode causing root galls.

Analysis of nutrient-disease interactions in rice:

• Zinc: Deficiency causes Khaira disease; not directly linked to blast resistance.
• Silicon: Silicon deposits as a thick silica-cellulose double layer beneath the cuticle in epidermal cells, acting as a physical shield against appressorial penetration by Magnaporthe oryzae (Pyricularia oryzae); hence higher silicon confers greater blast resistance (inverse relationship with susceptibility).
• Nitrogen: Directly increases blast susceptibility when applied in excess.
• Boron: Minor micronutrient.