An innovative integrated approach to characterize coffee resistance mechanisms to Colletotrichum kahawae

Doutoramento em Engenharia Agronómica - Instituto Superior de Agronomia - ULCoffee berry disease, caused by the hemibiotrophic fungus Colletotrichum kahawae, is a major constraint to Arabica coffee production in Africa. Coffee variety Catimor 88, which exhibit field resistance in Kenya, was selected to characterize the resistance to C. kahawae, comparatively to the susceptible variety Caturra. Hypocotyls of both varieties were challenged with C. kahawae (isolate Que2 from Kenya) and samples were collected during infection timecourse, simultaneously for analysis of fungal growth and plant responses (light microscopy), evaluation of enzymatic activities (spectrophotometry, electrophoresis, histochemistry) and gene expression analysis (quantitative real-time PCR). The resistance was characterized by restricted fungal growth associated with the hypersensitive reaction and early accumulation of phenolic-like compounds in the cell walls and cytoplasmic contents. Similar responses were detected in the susceptible variety but in a significantly lower percentage of infection sites. Regarding the genes related to the salicylic acid, jasmonic acid (JA) and ethylene (ET) pathways (phytohormones biosynthesis, reception, and responsiverelated genes), this study suggests the involvement of JA in the resistance while ET seems to be more related with the susceptibility. The expression of genes related to recognition and signaling (RLK, LRR-K, CML, PTL) and cell wall modification genes (PME41, MUR4) was induced in both coffee varieties, at early stages of the infection. However, in the resistant variety, a higher expression of recognition and signaling genes was induced together with the PME41 gene during fungal penetration, and the induction of expression of the Lignin-forming anionic peroxidase-like gene (PER4) was supported by the increase of total peroxidase activity and of an anionic isoform. Peroxidase was localized in the walls and cytoplasmic contents of host cells, at the infection sites. The new data obtained enable to identify potential biomarkers of disease resistance that, once validated, will be useful for marker-assisted selection in coffee breeding programmesN/