Analysis of Assertion A

Assertion A states that horizontal resistance is durable because it is non-race specific.

• Horizontal resistance (also known as non-specific or quantitative resistance) involves multiple genes and provides a general defense against a broad range of pathogen strains.
• Because it targets multiple pathogen functions or is based on general plant defense mechanisms, it is much harder for the pathogen to overcome quickly.
• This makes horizontal resistance generally more durable over time compared to race-specific resistance.

Therefore, Assertion A is correct.

Analysis of Reason R

Reason R states that race-specific resistance puts pressure on the pathogen to evolve more virulent races.

• Race-specific resistance (often controlled by single R genes) provides defense against particular races or strains of a pathogen that possess matching avirulence genes.
• When such resistance is deployed widely, pathogen populations that happen to have mutations allowing them to overcome that specific resistance are strongly selected for.
• This selection pressure drives the evolution of new, potentially more virulent or aggressive pathogen races capable of overcoming the host's specific defense.

Therefore, Reason R is correct.

Relationship between Assertion A and Reason R

While both statements are factually correct:

• Assertion A explains the durability of horizontal resistance based on its non-race-specific nature.
• Reason R explains a consequence (pathogen evolution pressure) associated with race-specific resistance.
• Reason R does not explain *why* horizontal resistance is durable. The durability of horizontal resistance stems from its broad-acting, multi-gene nature, not from the evolutionary pressures exerted on pathogens by race-specific resistance.

Thus, Reason R is not the correct explanation for Assertion A, even though both are true statements.