Day, P.
The system of naming physiologic races adopted for potato late blight (Black et al., Euphytica 2:173, 1953) and tomato late blight (Gallegly & Marvel, Phytopath. 45:103, 1955) can also be used for Cladosporium fulvum. The table below show the old and new race names. The new names are based on the tomato gene symbols proposed by Butler in TGC 3.
Tomato
Genotype Races of C. fulvum
Old 1 2 5 9 8 (10) 7 6
New 0 1 2 3 1,2 (1,3) 2,3 1,2,3
Cf+ s s s s s s s s
Cf\1 - s - - s s - s
Cf\2 - - s - s s - s
Cf\3 - - - s - s s s
Cf\1\Cf\2 - - - - s - - s
Cf\1\Cf\3 - - - - - s - s
Cf\2\Cf\3 - - - - - - s s
Cf\1\Cf\2\Cf\3 - - - - - - - s
- = resistant S = susceptible
The new race names reveal the elements of the gene-for-gene relationship
likely to be involved in this host-parasite association. Thus with n
resistance genes, 2^n races are possible. With the 3 genes now used to define
races of C. fulvum we know 7 of the 8 possible races. Race 10 or 1,3 is
hypothetical. The system is essentially a shorthand notation for physiologic
races illustrating their dependance on the host genes which define them. It
can be applied to a wide variety of crop plants and pathogens. When more than
4 or 5 host genes are involved the system is unwieldly. However in studying
the segregations of a few genes at a time, as is common in resistance breeding
programs, if the key races are named in relation to the genes under study
experimental data and thinking may be simplified.