Résumé
Black Leaf Streak Disease is a major leaf disease of banana caused by the airborne ascomycete Pseudocercospora fijiensis. A better understanding of the disease epidemiology would help to find alternatives to fungicides. According to empirical knowledge, plant infection is mainly due to the inoculum from outside the plot (external inoculum, supposedly ascospores) whereas the inoculum within the plot (internal inoculum, supposedly mainly conidia) plays a minor role. We propose to implement two complementary and original experimental approaches to (i) characterize and quantify the external and internal inocula of a plot, and (ii) to identify which leaves are infected by each inoculum. The study is carried out in Guadeloupe, on two experimental plots planted either with a susceptible or a partially resistant cultivar to reduce ascospore production. For the first aim, we install six Burkard multi-vial cyclone samplers above and under canopy to catch respectively the external and internal inocula. Then, we quantify conidia by microscopy and ascospores with quantitative PCR. For the second aim, we describe the leaf infection due to the external and internal inocula by comparing with image analysis the number of lesions produced on leaves, protected or not from the inocula with spore proof nets. The inocula and infection dynamics will be related to the cultivar and the microclimate. This study is the first contribution to understand the role of each inoculum in the leaves' infection.