Biology subjects

Ioos, R.

Publications and source records attributed to Ioos, R..

3 recordsLinked to original sources

bioRxiv2020

Ecological differentiation and incipient speciation in the fungal pathogen causing rice blast

Many invasive fungal species coexist as multiple lineages on the same host, but the factors underlying the origin and maintenance of population structure remain largely unknown. Here, we analyzed genetic and phenotypic diversity in isolates of the rice blast fungus (Pyricularia oryzae) covering a broad geographical range. We showed that the four lineages of P. oryzae were found in areas with different prevailing environmental conditions and types of rice grown, indicating niche separation. Pathogenicity tests revealed that specialization to rice subspecies contributed to niche separation between lineages, and differences in repertoires of putative virulence effectors were consistent with differences in host range. Experimental crosses revealed that female sterility and early post-mating genetic incompatibilities acted as strong barriers to gene flow between these lineages. Our results demonstrate that the spread of a pathogen across heterogeneous habitats and divergent populations of a crop species can lead to niche separation and reproductive isolation between distinct invasive lineages.

evolutionary biology↗

bioRxiv2019

Landscape epidemiology of ash dieback

Ash dieback caused by Hymenoscyphus fraxineus, an invasive alien pathogen, has been severely damaging European ash populations. Nevertheless, a large range of disease severities was observed at the landscape scale in the field. Several studies suggested that environment, such as climate, site conditions or local tree cover strongly affects ash dieback. We characterized the landscape epidemiology of the disease at two stages of the invasion process with spatio-temporal models using Bayesian models fitted by Integrated Nested Laplace Approximation (INLA). We first analyzed the effect of landscape features on the disease arrival and establishment stage at the scale of a village in NE France in 2012, 2 years after first report of the disease in the area and then, on the disease development stage in 2016-18. Landscape features had little impact on the disease at the establishment stage but strongly determined it further development. The local fragmentation of the tree cover was the most important factor with trees isolated or in hedges in agricultural settings far less affected then trees in forest environment. We showed that they were subjected to different microclimate with higher crown temperatures unfavorable to the pathogen development. Furthermore, host density was important for disease development with ash at low density far less affected by ash dieback. Presence of ashes in the vicinity affected local disease severity up to several hundred meters. These results may help to develop management strategy for the disease.

epidemiology↗

bioRxiv2017

The ash dieback invasion of Europe was founded by two individuals from a native population with huge adaptive potential

Accelerating international trade and climate change make pathogen spread an increasing concern. Hymenoscyphus fraxineus, the causal agent of ash dieback is one such pathogen, moving across continents and hosts from Asian to European ash. Most European common ash (Fraxinus excelsior) trees are highly susceptible to H. fraxineus although a small minority (~5%) evidently have partial resistance to dieback. We have assembled and annotated a draft of the H. fraxineus genome which approaches chromosome scale. Pathogen genetic diversity across Europe, and in Japan, reveals a tight bottleneck into Europe, though a signal of adaptive diversity remains in key host interaction genes (effectors). We find that the European population was founded by two divergent haploid individuals. Divergence between these haplotypes represents the 'shadow' of a large source population and subsequent introduction would greatly increase adaptive potential and the pathogen's threat. Thus, EU wide biological security measures remain an important part of the strategy to manage this disease.

genomics↗