Twenty-two wild Helianthus species and eight interspecific hybrids were evaluated for resistance to the leaf spot disease coused by Alternaria helianthi. Cultural characteristics of the fungal pathogen at temperature range of 20-30℃ and on medium with different carbohydrates were also studied. Colony growth of Alternaria helianthi was maximum on sunflower leaf extract medium (SLEM) devoid of carbohydrates while the maximum spore concentration with the largest conidiophore length (154.9 um) was obtained on SLEM with 2% sucrose. Temperature had significant effect on the colony growth but had no influence on the spore concentration and spore size. A simple, rapid and reliable laboratory technique using detached leaves for screening germplasm against Alternaria leaf spot has been developed to assist the field-based selection for resistant types. Significant differences were detected between various species for their reaction to Alternaria as measured by the percentage of leaf area infected. All diploid annuals and their hybrids were found highly susceptible. Maximum resistance was conferred by H. mollis, H. maximiliani, H. divaricatus, H. pauciflorus, H. tuberosus, H. resinosus and H. simulans. Field evaluation under artificial epiphytotic conditions revealed a close agreement in the reaction of the wild sunflowers to A. helianthi under both laboratory and field conditions.