A Fast and Easy Method to Study Virulence upon Transient Gene Expression or Gene Silencing in Leaves.

is a devastating soil-borne bacterial pathogen that causes disease in multiple host plants worldwide. Typical assays to measure virulence of in laboratory conditions rely on soil-drenching inoculation followed by observation and scoring of disease symptoms. Here, we describe a novel inoculation protocol to analyze the replication of upon infiltration into the leaves of , in which gene expression has been altered using . The protocol includes five major steps: 1) growth of plants; 2) infiltration of ; 3) inoculation; 4) sample collection and bacterial quantitation; 5) data analysis and representation. The transient gene expression or gene silencing prior to inoculation provides a straightforward way to perform genetic analysis of plant functions involved in the interaction between pathogen and host, using the appropriate combination of and strains, with high sensitivity and accuracy provided by the quantitation of bacterial numbers in plant tissues.