Competence of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> from Cruciferous Weeds and Wallflower (<Emphasis Type="Italic">Erysimum cheiri</Emphasis>) to Induce Black Rot in Cabbage

Aphanomyces euteiches Drechsler is an oomycete pathogen of leguminous crops that causes root rot, a severe disease of pea (Pisum sativum L.) worldwide. An improved understanding of the genetic structure of A. euteiches populations would increase knowledge of pathogen evolution and assist in the design of strategies to develop pea cultivars and germplasm with stable disease resistance. Twenty six primers pairs were used to amplify Sequence Related Amplified Polymorphisms (SRAP) among 49 A. euteiches isolates sampled from pea. A total of 190 polymorphic SRAP bands were generated, of which 82 were polymorphic between all the A. euteiches isolates. The percentage of polymorphic bands per primer pair ranged from 22 to 75%. According to the PIC value estimated for each marker, 60% of the SRAP markers were highly to reasonably informative (PIC > 0.25). Genetic structure of A. euteiches populations sampled in different American and French locations showed low to high genetic diversity within populations. The largest variation occurred within countries, with a total estimated genetic diversity of 0.477 and 0.172 for American and French populations, respectively. This was particularly evident from a principal component analysis (PCA) and a Minimum Spanning Networks (MSN) based on genetic profiles of isolates, which generated two different clusters, one corresponding to the French isolates and four American isolates (MV1, MV5, MV7, Ath3), and the other to American isolates. A. euteiches populations from cultivated pea in France appeared as a single unstructured population, whereas American isolates of A. euteiches diverged into three different populations.