Insights on plant and plant pathogen interactions led to great advances in understanding the mechanisms of disease resistance and susceptibility Plants and their pathogens have an intricate web of communications that affects the outcome of their interactions. Sometimes the pathogen is successful and can cause disease, while often the host plant displays successful resistance. Flor discovered a pattern of resistance known as the gene-for-gene concept in which a single gene of the plant pathogen corresponds to a single resistance gene of the host. This knowledge has proven invaluable in plant breeding where researchers use combinations of resistance genes to build cultivars resistant to the most dangerous strains of particular plant pathogens.