Several Japanese lines, like IRB 301-31, show a high level of resistance to the Fusarium oxysporum f. sp. radicis lycopersici (= FORL) This resistance comes from L. peruvianum PI 126944 and was introduced by backcrosses into cultivated tomatoes at the same time as the Tm-2 resistance gene to TMV (Yamakawa et al. 1987). This resistance to FORL is controlled by a gene for which the symbol Frl has been proposed (Vakalounakis 1988). A linkage between the resistance to FORL and the resistance by hypersensibility to TMV was demonstrated in cases of Tm-2 (Elkind et al. 1988) and Tm-2^nv and Tm-2^2 (Laterrot and Couteaudier 1989).
In order to check whether the resistance to FORL of IRB 301-31 and that of the lines Tm-2 and T^2 is controlled by the same gene, Frl, two allelism tests were carried out. The results are given in Tables 1 and 2.
The tests of resistance to FORL were carried out using a rapid method. The 18 day-old plantlets from sowing in steam-disinfected peat mould were pulled up and their roots were washed under tap water. The roots and the hypocotyl were then dipped for 5 minutes into a FORL conidia inoculum (106 conidia per ml of distilled water). The plantlets were then planted out in seed pans containing steam-sterilized silica sand and grown in a temperature-controlled chamber set for 22 D/16 N for 5 days, then 25 D/16 N, with 14 hours of light per day and fertilized watering (solution of Knop).
Five days after inoculation, the susceptible controls began to wither. Classification is carried out on the tenth day after inoculation. The plants were pulled up and the underground parts were washed. They were then classified into 5 categories as represented by the following classification scale on the hypocotyl:
Class of attack :
0 = healthy plant
1 = some necrotic specks
2 = many necrotic specks
3 = many specks plus some necrotic patches
4 = many necrotic patches
5 = plant dead, or almost dead
Depending on the agressivity of the isolates inoculated, the intensity
of the attack varied on the susceptible control plants, and also on the
resistant control plants and on the heterozygous resistance plants.In Table 1 are given the findings of an initial test concerning the links between resistance of the Moperou 161 line carrying Tm-2 and obtained from L. peruvianum PI 126926 (Laterrot 1987) and the gene Frl of IRB 301-31. Inoculation was carried out using a French isolate of FORL obtained by Y. Couteaudier (INRA-Dijon). Three pairs of Moperou and IRB 301-31 plants served as the basis of the test which can thus be considered as covering 3 repetitions. Not one susceptible plant was found among the 120 F2 plants (Moperou x IRB 301-31), nor among the 120 plants which resulted from the crossing of the F1 (Moperou x IRB 301-31) with the susceptible variety, Monalbo. A second test carried out with another French isolate which was less agressive, obtained by the GRISP (INRA-Avignon), gave similar results. Thus, the allelism of the resistant gene of Moperou and Frl can be concluded.
In Table 2 are given the findings of a test between Momor carrying the Tm-22 gene and obtained from the 630818 Alexander line, which had been in turn obtained from L. peruvianum PI 128650 (Laterrot 1987), and the Moperou line. Inoculation was carried out using a French isolate of FORL obtained by the GRISP (INRA-Avignon). As in the initial test, the study is based on the crossing of 3 pairs of plants. This test, which was carried out using an agressive isolate, did not reveal susceptible plants among the 120 F2 plants (Momor x Moperou), nor among the 120 plants resulting from the crossing of the F1 (Momor x Moperou) with the susceptible line, Monalbo. The same result was obtained in another test carried out using another, highly agressive, isolate. Thus, the allelism of the resistant genes of Momor and Moperou can be concluded.
It can thus be accepted, until proof to the contrary is forthcoming, that the resistance to FORL in Moperou and the gene in Momor are the gene Frl carried in IRB 301-31.
Literature cited :
Elkind, Y., N. Kedar, Y. Katan, Y. Couteaudier and H. Laterrot 1988. TGC Report 38:22
Laterrot, H. 1987. TGC Report 37:91
Laterrot, H. and Y. Couteaudier 1989. TGC Report 39:21
Vakalounakis, D.J. 1988. Plant Pathology 37 : 71-73
Yamakawa, K., H. Yasui, T. Mochizuki, K. Hida and S. Komochi 1987. Bull. Natl. Res. Inst. Veg. Ornam. plants and tea. Japan, Ser. A, N_ 1 : 1-37.
Table 1. Response of plant populations and lines after inoculation with FORL. Relation between Moperou and IRB 301-31 regarding resistance to FORL
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Populations or lines Number of plants by class
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0 1 2 3 4 5 Total
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F1 (Moperou x IRB 301-31) - 10 - - - - 10
F1 (Moperou x Monalbo) - 10 - - - - 10
F1 (Motelle x IRB 301-31) - 10 - - - - 10
F2 (Moperou x IRB 301-31) 1 - 38 2 - - - 40
F2 (Moperou x IRB 301-31) 2 - 32 8 - - - 40
F2 (Moperou x IRB 301-31) 3 - 40 - - - - 40
(F1(Moperou x IRB 301-31)1) - 38 2 - - - 40
x Monalbo
(F11(Moperou x IRB 301-31)2) - 39 1 - - - 40
x Monalbo
(F1(Moperou x IRB 301-31)3) - 40 - - - - 40
x Monalbo
Moperou - 10 - - - - 10
IRB 301-31 - 10 - - - - 10
Motelle - - - - 5 510
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Table 2. Response of plant populations and lines after inoculation with FORL.
Relation between Moperou and Momor regarding resistance to FORL.
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Population or lines Number of plants by class
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0 1 2 3 4 5 Total
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F1 (Momor x Moperou) - - 18 2 - - 20
F1 (Momor x Motelle) - 3 13 4 - - 20
F1 (Moperou x Monalbo) - - 8 12 - - 2
F2 (Momor x Moperou) 1 - 4 36 - - - 40
F2 (Momor x Moperou) 2 - 3 33 4 - - 40
F2 (Momor x Moperou) 3 - 10 30 - - - 40
(F1 Momor x Moperou) 1) - 26 14 - - - 40
x Monalbo
(F1 Momor x Moperou) 2) - - 25 15 - - 40
x Monalbo
(F1 Momor x Moperou) 3) - - 36 4 - - 40
x Monalbo
Momor - 10 9 1 - - 20
Moperou - 4 16 - - - 20
IRB 301-31 - 9 3 8 - - 20
Monalbo - - - - - 16 16
Motelle - - - - - 20 20
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