Plant pathogens are specialized organisms that can manipulate and/or suppress plant immunity. Effectors are small-secreted proteins that are induced during plant infection and are essential factors for the manipulation of plant immunity. Verticillium dahliae is a soil-borne fungus that causes Verticillium wilt disease in a more than 200 plants. V. dahliae strains are assigned to ¿pathotypes¿ based on their virulence on a particular host. For instance, V. dahliae strains that are highly virulent and cause rapid and severe defoliation on cotton (Gossypium hirsutum) and olive (Olea europaea) are referred to as strains of the defoliating (D) pathotype; the strains that are less virulent and only induce wilting symptoms without defoliation on the same host are referred as non-defoliating (ND) pathotype.
In the last few years, several V. dahliae genomes were sequenced in order to identify the gene causing defoliation on cotton and olives tree. In 2012, a research activity was initiated by the project lead in Thomma`s group at the Laboratory of Phytopathology of the Wageningen University (the Netherlands), which led to the identification of the causal gene for defoliation (D-gene) in cotton upon Verticillium dahliae infection. Subsequently, homologues to the V. dahliae D-gene were identified in other Verticillium species like V. alfalfae and V. longisporum and in more unrelated soil-borne pathogens belonging to Fusarium spp.
Soil-borne pathogens are notoriously difficult to eradicate from the soil and few fungicides can be applied to control the related disease. Therefore, the most used strategy to manage soil-borne pathogen is to breed for resistant plants. The project aims to the understanding of the role of the D-gene during Verticillium and Fusarium infection, its way of action in plant and, therefore, exploit the knowledge to suggest a breeding strategy against fungal species carrying the D-gene.
Wilt diseases caused by Verticillium and Fusarium are hardly controlled with fungicides; these are generally ineffective to eliminate the fungus from infected plants once it has entered xylem vessels. Moreover, these pathogen produces long-term resistance structures ensuring its resilient survival in the soil. Therefore, resistant plants are the only solution to the control these two pathogens.
Resistance genes are widely used to controll Fusarium wilt disease on different crops including melon, cucumber and water melon. However, R gene confers resistance to a restricted spectrum of Fusarium oysporum races. For example, the resistance gene Fom-1 of melon confers resistance to Fusarium oxysporum f. sp. melonis race 1 while Fom-2 protein confer resistance to race 2. Similarly, three R genes against F. oxysporum f. sp. niveum have been identified in watermelon but all of them are ineffective against the new emerging F. oxysporum f. sp. niveum race 3. Additionally, all effectors recognized by these resistance proteins are formae speciales and race specific.
In contrast to race specific effector that are recognized by different R proteins, the D protein is an uquitinious effector that may target the same protein in all cucurbit plants. The confirmation to this hypotesys would allow a new breeding strategy where breeders would select for plant with variant of the D protein target. This would allow for broad spectrum resistance against Fusarium ff. spp. by breeding only a single gene.