Wild species of sunflower (Helianthus annuus) play an important role in the genetic improvement of this oleaginous crop since they have different characters of economic importance to be transferred into the cultivated form using interespecific hybridization. The purpose of our present research program is to preserve and characterize the genetic resources of both naturalized and exotic wild sunflowers having an agronomic interest. One of the first steps was to describe different accessions of annual wild species for biotic stress in order to detect potential resistance sources. H. petiolaris is one of the wild sunflower species that can be found in Argentina and we had selected before a certain number of these species on the basis of their Sclerotinia sclerotiorum responses on leaves and stems. This genetic material was then inoculated on leaves and stems but with Phomopsis helianthi, a fungus which produce stem canker in sunflower. This work shows the variability of brown necrotic responses after Phomopsis inoculations on H. petiolaris leaves and stems. Some half-sib families were detected to have good disease tolerance to Phomopsis as well as Sclerotinia and they will be backcrossed in order to increase the diversity for this disease resistance in the cultivated germplasm.