Diversity of the Pythium community infecting crown and roots apple in Tunisia

The genus Pythium is important in agriculture, since it contains many plantpathogenic species. Little is known about the diversity of Pythium species causing appledicline. Therefore, the aim of the study was to characterize 21 Pythium isolates collectedfrom root and collar rot apple trees in Tunisia from 2006 through to 2009. The isolateswere characterized morphologically as well as through sequence analyze of the internaltranscribed spacer region (ITS). Three Pythium species were identified in this study P.rostratifingens, P. undulatum and P. sterilum. In virulence assays on excised apple twigsand in the fields, representative isolates of the different Pythium species isolated werepathogenic on the Anna, Lorka and Meski varieties and the MM106 rootstock. Resultsobtained show the great susceptibility of the MM106 rootstock to the infections for thedifferent Pythium species tested.