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Thesis started november 1st, 2016. Defended in decembre, 2019 11^th
Funding: Région Bretagne - Agrocampus Ouest
Direction: Christophe Le May, Didier Andrivon

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Abstract:

Any host plant is subjected, throughout its life, to the simultaneous or sequential pressure of infection by various pathogens, whose coexistence leads to competitive interactions able to affect epidemiological dynamics. The main objective of this work is to assess the impact of the coexistence of Peyronellaea (ex Didymella) pinodes (Dp) and Phoma medicaginis var. pinodella (Pmp), two key agents of pea Ascochyta blight, on their epidemic development. Our results suggest that the coexistence of both fungal species derives from three distinct life history and host exploitation strategies. Most Dp strains are ‘pioneer colonizers’, allowing them to develop first on young hosts. These early attacks weaken the plant, and favor later infection by Pmp and rare Dp strains boasting a ‘scavenger’ strategy on vulnerable host tissue. The remaining Pmp and Dp strains display an ‘intermediate’ strategy, and act as opportunists. We also showed that both direct and indirect competition alter these life strategies. However, for each type of competition, host exploitation strategies vary in the same direction irrespective of the kind of competitor, although the intensity of the variation depends on the genetic relatedness between competitors. We therefore show the strong impact of competitive interactions on coexistence and virulence, so that the management of epidemics would benefit from a full understanding and use of underlying mechanisms.

Poster pdf