Genetics of Meloidogyne virulence against resistance Genes from Solanaceous crops
Résumé
The genetic basis of plant-pathogen interaction is built on the gene-for-gene concept (Flor, 1942), which states that for each gene conferring resistance in the host plant, there is a matching or complementary gene in the pathogen, called an avirulence gene. In this hypothesis, both plant resistance gene and pathogen avirulence gene are dominant (Gabriel and Rolfe, 1990), and only the confrontation between both dominant alleles results in the hypersensitive reaction in the plant, often associated with a cascade of other defence responses (Figure 1). The gene-for-gene complementarity occurs most frequently in plant-pathogen interactions involving obligate and biotrophic parasites which are highly specialized and have a narrow host range (Heath, 1981; Keen, 1982). Since Flor’s work in the 1940s, many avirulence genes have been identified by classical genetic studies in plant-pathogen interactions including viruses, bacteria, fungi, insects and nematodes (Sidhu, 1987), but only recently have they been cloned and characterized in the cases of viruses, bacteria, and more recently fungi. The first bacterial avirulence gene cloned was avrA from Pseudomonas syringae (Staskawicz et al., 1984), the first viral avirulence gene cloned was the coat protein gene of the tobacco mosaic virus (Culver and Dawson, 1991), and the first fungal avirulence gene cloned was avr9 from Cladosporium fulvum (Van Kan et al., 1991).