The tomato Cf-4 and Cf-9 genes confer resistance to the leaf mould pathogen Cladosporium fulvum and map at a complex locus on the short arm of chromosome 1. It was previously shown that the gene encoding Cf-4, which recognizes the Avr4 avirulence determinant, is one of five tandemly duplicated homologous genes (Hcr9-4s) at this locus. Cf-4 was identified by molecular analysis of rare Cf-4/Cf-9 disease-sensitive recombinants and by complementation analysis. The analysis did not exclude the possibility that an additional gene(s) located distal to Cf-4 may also confer resistance to C. fulvum. We demonstrate that a number of Dissociation-tagged Cf-4 mutants, identified on the basis of their insensitivity to Avr4, are still resistant to infection by C. fulvum race 5. Molecular analysis of 16 Cf-4 mutants, most of which have small chromosomal deletions in this region, suggested the additional resistance specificity is encoded by Hcr9-4E. Hcr9-4E recognizes a novel C. fulvum avirulence determinant that we have designated Avr4E.
Takken, F. L. W., Thomas, C. M., Joosten, M. H. A. J., Golstein, C., Westerink, N., Hille, J., ... Jones, J. D. G. (1999). A second gene at the tomato of Cf-4 locus confers resistance to Cladosporium fulvum through recognition of a novel avirulence determinant. Plant Journal, 20, 279-288. https://doi.org/10.1046/j.1365-313X.1999.00601.x