Question

. Why a plant pathogen carries a avirulent gene

Answer 1

Answer:

There is strong indirect evidence that many, if not nearly all, Avr proteins are secreted from pathogenic bacteria, enter plant cells and signal a response phenotype, usually associated with a hypersensitive defense response (HR). ...

Answer 2

Answer:

Avr genes have dual functions: Pathogens containing Avr genes are avirulent to plants carrying the matching R genes, while they are virulent in race, strain, pathovar or species-specific way to plants without carrying the matching R genes