Sunflower downy mildew: a persistent threat

This work was funded by inter-unit funding from LabEx TULIP-FRAIB.

Translation from : https://www.inrae.fr/actualites/mildiou-du-tournesol-menace-persistante

The evolutionary history of sunflower downy mildew...

Sunflowers are an important oilseed crop in Europe, particularly in France. The species originated in North America, where Native Americans cultivated it extensively before its relatively recent conversion to a field crop in Eastern Europe. The rise of sunflowers in France dates back to the 1960s. However, their cultivation has been largely limited by numerous pathogens introduced from their native range in the United States, particularly an oomycete, Plasmopara halstedii, which causes downy mildew.

Sunflower downy mildew: 1) Symptoms of the disease: stunted plant with mosaic patterns and white sporulation on the leaves
2) Sporulation of Plasmopara halstedii downy mildew at a leaf stomata
(scanning electron microscopy) © L. Godiard – INRAE

… serving crop resilience

In this study, the team traced the evolutionary history of Plasmopara halstedii in France using genome analysis of the 16 currently recognized reference pathogen families and records of their presence in fields since the 1960s. Analysis of this data enabled the identification of the founding strains and their recombinant strains, as well as the genomic regions associated with the circumvention of sunflower resistance genes.

The results shed light on the evolutionary mechanisms underlying the adaptation of plant pathogens to their hosts. In the case of sunflower downy mildew, the importance of sexual reproduction, which allows genetic mixing between recurrently introduced strains, becomes apparent, something that had never been clearly demonstrated before. This could play a role in the management of the pathogen, which until recently was still considered a regulated organism.

This work also illustrates the consequences of deploying crop resistance on pathogen adaptation. More broadly, it can serve as a reference for the sustainable management of crop resistance for sunflowers, but also for other crops affected by pathogens.

Confronted with intensifying environmental pressures in agriculture, this study highlights the need for a more sustainable and rational deployment of resistance genes present in plants, which would also limit the use of plant protection products.