Thesis started octobre 1st, 2011, defended in april 10^th 2015
Fund: Grant from the French Ministry of Higher Education and Research
Direction: Sylvain Fournet, Eric Petit and Jean-François Arnaud

Abstract:

Nowadays, favored methods of control of pest populations involve environmentally friendly methods, such as genetic resistances. The genetic diversity of field populations is one factor that may be considered for the development and use of sustainable resistances because it will condition pathogen population ability to disrupt resistance genes. Genetic diversity of crop phytoparasites results from the combination of their evolutionary history on historical wild host plants and of current gene flow occurring between wild hosts and crop fields and among field populations. Wild pathogen populations may therefore have a strong influence on genetic diversity and on their adaptation potential to resistances genes.

The Heterodera schachtii and Heterodera betae/Sugar beet complex is particularly suited to investigate this question. Indeed, both nematode species are damaging sugar beet crops in Europe but are also growing on the wild sea beet Beta maritima, which is distributed all along the Atlantic coastline from the south of Spain to the north of Sweden. This wild beet is the main source of resistance used by beet seed companies, and is supposed to be one of the historical hosts of both species. Preliminary studies carried out on wild nematodes populations collected on Beta maritima have shown that H. betae and H. schachtii populations do not exhibit similar genetic structures on their wild host, which may have consequences for the durability of resistances developed against these pests. In this context, we (1) develop a comparative phylogeographic approach to study the differences in the genetic diversity and distribution of both nematodes species in wild and field populations, and (2) investigate the factors (gene flow, reproduction mode, etc) involved in those differences.