Secondly, any such pathogen race that undergoes an additional mutation to overcome another R gene is likely to be less fit than a race that can overcome only one R gene, because avr gene are likely to encode pathogenicity factors.
Secondly, any such pathogen race that undergoes an additional mutation to overcome another R gene islikely to be less fit than a race that can overcome only one R gene, because avr gene are likely to encodepathogenicity factors.