Disease EMergence in an isolated Environment : understanding Transmission to control Epidemics in Rice – DEMETERice

Disease outbreaks are a major threat to humans, animals and plants. In the absence of treatments, vaccines or resistant varieties, preventing the transmission of pathogens appears to be the main alternative to control their spread, limit their impact and to prevent new introductions. Rice is one of the most important cereals feeding half of the world. Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae (Xoo) threatens rice production. Although BLB has been extensively studied, little is known about Xoo life cycle. It is generally accepted that wind, water and wounds participate to its dispersal but has never been investigated. Moreover, the possibility of its transmission by seed has never been formally demonstrated. In 2019, we have reported the first identification of BLB in Madagascar, a country where 90% of agricultural activity relies on rice production. Preliminary microsatellites genotyping of Malagasy strains strongly suggests a role for seeds in the introduction and the rapid dispersal of the disease at country level. In this context, this project aims to assess the role of seed transmission at a multidimensional scale in the emergence and spread of a major rice disease. The epidemiological context of BLB in Madagascar will serve as a model because (i) the recent and unique introduction of the bacteria will allow to monitor in real time pathogen dispersal and its evolutionary potential to adapt to contrasted environment, (ii) an island provides an interesting isolated system to study epidemics, (iii) according to the socio-economic importance of rice cultivation in Madagascar, it is urgent to generate knowledge that could guide an integrated control of BLB. Specifically, this project aims to experimentally validate the ability of Xoo to be transmitted by seeds, to evaluate the role of seeds in disease spread at the national level and to determine the importance of seed transmission relative to other modes of transmission.