The necrotic reaction of all lines carrying Pto after spraying of the foliage with Fenthion insecticide (Laterrot and Moretti, 1989) gives rise to two hypotheses: either the existence of a very close linkage between this reaction (the gene responsable for the latter may be referred to as Fen) and the Pto gene, or a shared genetic control of the reaction to Fenthion and resistance to Pseudomonas tomato. A second gene - Pto-2 - which is independent in relation to Pto and which controls bacteria was found in the L. pimpinellifolium accession PI 126430 (Pilowsky and Zutra, 1982, 1986) and was introduced to the species grown.
The necrotic reaction to Fenthion of PI 126430 (batch received from the Volcani Centre in 1981) which was observed in our tests, followed by the same reaction of the line 'Volcani 2671' obtained from PI 126430 (Lapushner et al., 1988), caused us to carry out an allelism test between the 'Volcani 2671' and 'Ontario 7710' (received from Simcoe Station) carrying the Pto gene.
The test was carried out in two stages, one with P. tomato, the other with Fenthion. The first part of the test was carried out in glasshouses on 18-day-old plantlets by spraying with an inoculum made up of a mixture of 5 isolates collected in France by B. Rat (INRA-Angers). The second part of the test was carried out in glasshouses on 16-day-old plantlets by spraying with the liquid commercially-available product, "Lebaycid", at a concentration of 1.5 ml/l of liquid Lebaycid. Three pairs of 'Volcani 2671' and 'Ontario 7710' plants served as the basis of the test which can thus be considered as covering 3 repetitions.
The results are given in Table 1. Classification of the plants for their reaction to the bacteria one week after the inoculation was simple as the test was only slightly agressive and very discriminating. The plants showed either no symptoms in the case of the resistant lines, or 3-to-20 typical lesions in the susceptible Monalbo control. Classification of necroses caused by Fenthion was carried out 4 days after spraying.
No segregation was apparent, whether in relation to P. tomato or after spraying with Fenthion. This was true for the F2 populations but also for the plants obtained by crossing the F1 plants with the susceptible line, 'Monalbo'. It can thus be accepted that the 'Volcani 2671' line carries the same Pto gene as the 'Ontario 7710' line.
Literature cited :
Laterrot, H. and A. Moretti 1989. TGC Report 39 : 21-22
Lapushner, D.M., M. Pilowsky , G. Nehama, W.H. Lindhout and R. Frankel, 1988. TGC Report 38 : 28
Pilowsky, M. and D. Zutra 1982. TGC Report 32 : 42
Pilowsky, M. and D. Zutra, 1986. Phytoparasitica 14 (1) : 39-42
Table 1. Response (number of plants) of plant populations and lines after inoculation with Pseudomonas tomato and after spraying with Fenthion insecticide
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P. tomato test Fenthion test
Populations or lines Healthy Diseased No symptoms Necrosed
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F1 (Ontario 7710 x Volcani 2671)1 16 - - 8
F1 (Ontario 7710 x Volcani 2671)2 29 - - 16
F1 (Ontario 7710 x Volcani 2671)3 32 - - 16
F1 (Monalbo x Ontario 7710) 26 - - 23
F2 (Ontario 7710 x Volcani 2671)1 30 - - 30
F2 (Ontario 7710 x Volcani 2671)2 47 - - 30
F2 (Ontario 7710 x Volcani 2671)3 45 - - 30
(F1 (Ont 7710 x Volcani 2671)1) x
Monalbo 47 - - 30
(F1 (Ont 7710 x Volcani 2671)2) x
Monalbo 48 - - 30
(F1 (Ont 7710 x Volcani 2671)3) x
Monalbo 42 - - 30
Ontario 7710 34 - - 24
Volcani 2671 48 - - 34
Monalbo (P. tomato susceptible
control) - 41 24 -
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