These genotypes were mechanically inoculated with 12 different strains of PVY isolated from various hosts collected from various geographical locations (Legnani 1995). For each experiment ten, twenty one day old plants of each accession were inoculated and DAS ELISA tests were performed 15 days after inoculation on each plant. These experiments were repeat twice.   We propose to name the different pathotypes according to the triplet code nomenclature described by Limpert et al 1994. According to these results, 7 degrees of virulence of PVY are revealed with the range of tomato used. The strain CAA 16 (isolated from Pepper in Italy) is not able to infect the tested tomato lines. Until now this is the first report of a strain of PVY unable to infect tomato. This strain is the sole member of pathotype tentatively named 0.0. The strain LYE 90 (Tomato, California) is able to infect Momor but not the other tested genotypes. This strain is the sole member of the pathotype tentatively named 1.0. The strain SOTOR (Potato, France) is able to infect Momor, PI 134417, Micro Tom but not the other tested genotypes. This strain is the sole member of the pathotype tentatively named 7.0. The strain NIG 1 (Tobacco, California) is able to infect Momor, PI 134417 and PI 128660 but is not able to infect Micro Tom, Sweet 100, Sweet Million, PI 126410, Angela 18.1 and PI 247087. This strain is the sole member of the pathotype tentatively named 3.1. The strain SOT 10 (Potato, Morocco) is able to infect Momor, PI 134417, Micro Tom, PI 128660 but is unable to infect Angela 18.1. This strain is also the sole member of the pathotype tentatively named 7.1. The strains SOTNV1 (Potato, France), SOTNTNLb (Potato, Liban), LYE 66 (Tomato, France), LYE 82N (Tomato, France), LYE 84 (Tomato, Cannary Islands) infect all genotypes except PI 247087. These strains belonged to the pathotype tentatively named 7.3. The strains LYE 84.2 (Tomato, France) and LYE 190 (Tomato, France) are able to infect all tested genotypes (Legnani 1995). These strains belonged to the pathotype tentatively named 7.7. These two strains were isolated from infected plants of selected lines obtained from PI 247087. To our knowledge this is the first report of a strain of PVY able to overcome the mechanism of resistance (cell to cell movement) expressed in 21 day old plants of L. hirsutum PI 247087. However, a previously described mechanism of resistance to long distance movement expressed in 45 day old plants of PI 247087 (Legnani et al 1995) is efficient against pathotype 7.7.

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