Among the sources of resistance to Fulvia fulva (= Cladosporium fulvum) which were exposed to more than a hundred isolates of the fungus, 2 lines received from E.A. Kerr in 1980 show a similar reaction which suggests the existence of an allelic relationship between the resistance factors of these 2 lines. The lines concerned are Ontario 792 (Cf-10) and Ontario 798 (Cf-12).
We carried out an allelism test, the results of which are given in Table 1. The test was carried out using a Cladosporium isolate belonging to race 0 and which was isolated in 1986 from open field grown tomatoes at Sarrians, in south-eastern France. This isolate is highly sporulant. Three pairs of Ontario 792 and Ontario 798 plants served as the basis of the test which can thus be considered as covering 3 repetitions.
Out of the 178 F2 plants (ONT 792 x ONT 798), 10 susceptible plants were observed. Thus the two factors are not allelic and these results suggest that the factors are independent (X^2 = 0.11; P = 0.75, taking as hypothesis 15 resistant plants : 1 susceptible plant), contrary to the deductions which can be drawn from the notes of Kanwar et al. (1980a, b), which were questioned by Kerr (1982).
Table 1 : Response of plant populations and lines after inoculation with a race 0 Cladosporium isolate
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Populations or lines Number of plants by class
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I B BS S SS SSS TOTAL
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F1 (ONT 792 x ONT 798) 1 16 - - - - - 16
F1 (ONT 792 x ONT 798) 2 16 - - - - - 16
F1 (ONT 792 x ONT 798) 3 7 - - - - - 7
F2 (ONT 792 x ONT 798) 1 55 1 - - - 4 60
F2 (ONT 792 x ONT 798) 2 52 4 1 - - 3 60
F2 (ONT 792 x ONT 798) 3 54 - 1 - 1 2 58
Ontario 792 (Cf-10) 15 1 - - - - 16
Ontario 798 (Cf-12) 7 4 - - - - 11
Monalbo (susceptible line) - - - - - 13 13
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Class of attack: I : no symptoms
B : white specks with abundant mycelium
BS : the same as B plus some sporulation
S : moderate sporulation
SS : heavy sporulation
SSS : very heavy sporulation
Literature cited :Kanwar, J.S., E.A. Kerr and P.M. Harney 1980 a. TGC Report 30. 20-21
Kanwar, J.S., E.A. Kerr and P.M. Harney 1980 b. TGC Report 30 : 22-23
Kerr E.A., 1982. TGC Report 32 : 19