Effector-based selection for the tolerance to Corynespora Leaf Fall: is cassiicolin a good candidate?

Archive ouverte

Pujade-Renaud, Valérie, V. | Ribeiro, Sébastien | Tran, Dinh Minh | Deon, Marine | Garcia, Dominique, D. | Lopez, David | Soumahoro, Mouman | Masson, Aurélien

Edité par CCSD -

International audience. The Corynespora Leaf Fall (CLF) disease of rubber tree, caused by the necrotrophic fungus Corynespora cassiicola, has become an important concern for rubber planters in Asia and Africa. In highly susceptible clones, the defoliation of young leaves induces yield erosion over years. While some plantations try to control the disease with fungicides, others choose to uproot the diseased clones and replace them with less susceptible ones. The selection and development of tolerant clones appears as an interesting strategy to control the disease. To speed up the breeding process, an indirect phenotyping procedure can be used: it consists in testing the sensitivity to the fungal toxins (or effectors) rather than the susceptibility to the fungus itself. This strategy requires precise identification of the effectors responsible for the virulence of a given isolate. Cassiicolin, a small, secreted protein, was for long suspected to play a role in the virulence of isolate CCP in rubber tree. Sensitivity of detached rubber leaves to the purified cassiicolin (extracted from CCP culture filtrate) was found to be correlated to the susceptibility to CCP (inoculated as a spore suspension), on a range of clones.Here we show that deletion of the cassiicolin gene in isolate CCP results in a total loss of virulence. This clearly demonstrates that cassicolin is indeed a necrotrophic effector required for the virulence of isolate CCP in rubber tree. However, we know that a number of C. cassiicola isolates do not have a cassiicolin gene, and that this effector is polymorphic, with potentially seven isoforms. We have thus analyzed the typology of a large set of C. cassiicola isolates collected from various rubber plantations in West Africa. Our results show that isolates carrying the cassiicolin isoform Cas1 are widely represented, but that the most represented type (A/Cas0) are isolates without cassiicolin gene. In conclusion, we think that the necrotrophic effector Cas1 can be an interesting tool for effector-based selection of tolerant clones for African plantations; however, efforts should also be placed on A/Cas0 isolates, in order to identify the necrotrophic effector(s) responsible for their virulence. This would enlarge the potential of effector-based selection.

• Description
• Sujet/Public
• Outil
• Outil d'anticipation
• Mémoire et thèse
• Gestion