Molecular and phenotypic characterisation of French isolates of Diaporthe helianthi / Phomopsis helianthi Munt.-Cvet

Among a French collection of 150 Diaporthe helianthi / Phomopsis helianthi Munt.-Cvet. isolates collected on sunflower since 1995, 4 were chosen for their different characteristics according to their geographic origin and the part of the infected plant where they were sampled (leaf, petiole, capitulum). Phenotypic and molecular characterisation studies were conducted on these isolates. Phenotypic studies corresponded to their linear and ponderal growths, their morphology in culture on agar medium and their aggressiveness on sunflower leaf and stem through artificial contaminations in the field. Molecular characterisation concerned on one hand the whole genome (AFLP) and on the other hand the ITS sequences. The 4 isolates present phenotypic differences in their growth in vitro, their morphology (ability to differentiate perithecia) and their aggressiveness on sunflower. Similar variability was also observed in AFLP analyses of the D./P. helianthi genome. This fungus appears to have a genome of variable size. In contrast, ITS sequences (concerning only a part of the genome) did not show differences between the 4 isolates, confirming that they do belong to probably the same species.