• Biological Control via Hypovirulence: Hypovirulence refers to a stable, transmissible reduction in virulence of fungal pathogens, famously observed in the chestnut blight fungus Cryphonectria parasitica.
• Molecular Basis: Hypovirulent strains harbor persistent fungal mycoviruses (family Hypoviridae) that consist of double-stranded RNA (dsRNA) elements residing in the fungal cytoplasm.
• Mechanism: These unencapsidated dsRNA elements suppress fungal expression of virulence factors (such as laccase, oxalic acid, and pheromones), converting aggressive blight strains into benign saprophytic strains that transmit hypovirulence to virulent strains via hyphal anastomosis.
• Conclusion: Hypovirulent strains contain double-stranded RNA elements (Option 2).

Correct option: (2) Double stranded RNA elements

• The Phenomenon of Cross-Protection: Cross-protection (or pre-immunization) is a systemic plant phenomenon in which prior systemic infection of a plant with a mild strain of a pathogen protects the host from subsequent severe disease induced by a challenge infection with a severe, related strain.
• Group of Pathogens: Cross-protection is predominantly and classically observed in plant viruses (e.g., Citrus tristeza virus, Papaya ringspot virus, Tobacco mosaic virus).
• Mechanism: The mild viral strain accumulates coat protein or produces specific viral siRNAs via RNA silencing that immediately target and degrade incoming closely related viral genomes upon entry.
• Conclusion: Cross-protection is most common in viruses (Option 2).

Correct option: (2) Viruses

• Hormonal Cross-Talk in Plant Immune Signaling:
• Statement (I) is true: The Salicylic Acid (SA) signaling pathway (activated by biotrophic pathogens) and the Jasmonic Acid (JA) pathway (activated by necrotrophs and chewing insects) exhibit classic mutual antagonism. Activation of the SA pathway via NPR1 down-regulates JA-responsive genes (e.g., PDF1.2), preventing excessive energy expenditure on redundant defenses.
• Statement (II) is true: Salicylic acid and Auxin signaling are mutually antagonistic. Auxin signaling promotes disease susceptibility by stimulating expansins and cell-wall loosening (favoring bacterial colonization); SA actively represses auxin receptor expression (TIR1) and stabilizes Aux/IAA repressors to boost plant immunity.
• Conclusion: Both Statement (I) and Statement (II) are true (Option 1).

Correct option: (1) Both Statement (I) and Statement (II) are true.

• Pathogen-Derived Resistance (PDR) in Transgenic Crops:
• Sanford and Johnston Hypothesis (1985): Concept that expressing pathogen-derived genetic sequences in a host plant confers durable genetic resistance.
• The Papaya Ringspot Virus Triumph: The most celebrated commercial success of PDR is Rainbow and SunUp papaya developed by Dennis Gonsalves and colleagues in Hawaii (1998) to manage devastating Papaya Ringspot Virus (PRSV) by engineering plants with the viral coat protein gene, which saved the Hawaiian papaya industry through RNAi-mediated protection.
• Conclusion: Papaya Ringspot is managed through Pathogen-Derived Resistance (Option 3).

Correct option: (3) Ring Spot of papaya