ldentification of Two Genes Required in Tomato for Full Cf-9-Dependent Resistance to Cladosporium fulvum

Mutagenesis was used to identify and characterire plant genes required for fungal disease resistance gene function in tomato. Seed of a stock homozygous for the Cf-9 gene for resistance to Cladosporium fulwum were treated with ethyl methanesulfonate, and 568 M2 families were screened for mutations to C. fulvum sensitivity. Eight mutants with reduced resistance were isolated. Four mutations, all of which mapped to the Cf-9 gene, lost both resistance and response to the race-specific AVRS elicitor. The other four mutations partially lost resistance and response to the AVRS elicitor. Cyto-logical analysis revealed that a unique host cell staining pattern accompanied the reduced-resistance phenotype in three mutants. Two of the mutants with reduced resistance mapped to Cf-9, and two mapped to two distinct loci designated Rcr-7 and Rcr-2 mequired for Cladosporium yesistance) that are unlinked to Cf-9