Figure 4. The receptor-elicitor model of gene-for-gene interactions. The resistance allele of the plant encodes a receptor that recognizes an elicitor produced by the pathogen. Recognition of the pathogen elicitor by the plant receptor initiates plant defense responses that lead to plant resistance. If the pathogen produces the elicitor, it is avirulent. If the pathogen does not produce the elicitor, it is virulent.