What characterizes race-specific resistance in plants?

Race-specific resistance in plants refers to the ability of certain plant varieties to defend themselves against specific strains or races of pathogens while being susceptible to others. This type of resistance is often governed by specific plant genes that interact with corresponding avirulence genes in the pathogen. When a pathogen strain expresses the relevant avirulence gene, the plant recognizes the pathogen and mounts a defensive response, effectively thwarting the infection.

This form of resistance is vital for plant breeding programs, as it helps to maintain high levels of crop yield in the face of specific pathogen challenges. However, because it is tailored to specific pathogen races, it can lead to the vulnerability of the plant if the pathogen evolves or if a new race emerges that is not recognized by the plant's defenses. Understanding these dynamics is crucial for effective pest management in agricultural systems, as it can guide the selection of plant varieties for crop production.

The other options describe different attributes of resistance that do not fit the definition of race-specific resistance. Resistance to multiple races indicates a broader defensive capability, while resistance that develops over time suggests a change in the plant's response rather than a specific genetic interaction. Broad-spectrum resistance implies a wider range of effectiveness against various pathogens, contrasting with the targeted nature of race-specific resistance.