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The Am Gene Controlling Resistance to Alfalfa mosaic virus in Tomato Is Located in the Cluster of Dominant Resistance Genes on Chromosome 6

April 2004 , Volume 94 , Number  4
Pages  345 - 350

Giuseppe Parrella , André Moretti , Patrick Gognalons , Marie-Laure Lesage , George Marchoux , Kashay Gebre-Selassie , and Carole Caranta

First, second, fourth, and seventh authors: Institut National de la Recherche Agronomique (INRA), Genetics and Breeding of Fruits and Vegetable; and third, fifth, and sixth authors: INRA, Plant Pathology, Dom. St Maurice, BP94, F-84143 Montfavet Cedex, France

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Accepted for publication 26 November 2003.

The dominant gene Am from Lycopersicon hirsutum f. sp. glabratum PI134417 confers resistance to most strains of Alfalfa mosaic virus, including the recently identified necrotic strains. The phenotypic response includes a lack of symptom development following mechanical inoculation of leaves. To study the resistance mechanism controlled by Am, biological (back-inoculation to susceptible hosts), serological (double-antibody sandwich, enzyme-linked immunosorbent assay), and molecular (reverse transcription-polymerase chain reaction and hybridization with specific riboprobes) methods of virus detection have been conducted on mechanically inoculated PI134417 leaves. The virus was never recovered, indicating that Am acts by an inhibition of viral accumulation during the early events of the virus life cycle. Am has been mapped genetically to the short arm of tomato chromosome 6 in the resistance hotspot, which includes the R-genes Mi and Cf-2/Cf-5 and the quantitative resistance factors Ty-1, Ol-1, and Bw-5.

Additional keywords: disease resistance, gene clustering, gene mapping, introgression lines, resistance mechanism.

© 2004 The American Phytopathological Society