Nonhost resistance genes and race-specific resistance.

Apart from physical barriers, plants have two major types of defense against potential pathogens. In 'race-specific' resistance, plants match single mendelian resistance genes with the 'avirulence' genes possessed by races of a pathogen. Plants also employ the more complex and evolutionarily more robust system of 'nonhost resistance' against a broad range of pathogenic species. In peas, both types of resistance are associated with the expression of a common group of 'resistance response' genes.