Introduction: Damping-off caused by Pythium aphanidermatum is one of the major diseases of luffa. Identifying and planting of resistant varieties is an environmentally friendly solution for integrated disease management. This study was conducted to determine the reaction of eight native and non-native luffa genotypes to the disease. Materials and Methods: The pathogen (Pythium aphanidermatum IRAN597C) was obtained from the collection of fungi of the Iranian Institute of Plant Protection Researches. It was inoculated into seedlings of eight luffa genotypes. After the appearance of yellowing symptoms and seedling death, the disease index (DI) and the area under the disease progression curve (AUDPC) were calculated for each genotype. Koch's postulates were carried out to prove pathogenicity and the pathogen was isolated from diseased seedlings. Then, for molecular confirmation of the pathogen, ITS-rDNA sequencing was used. Results: The sequencing of the ITS-rDNA region of the pathogen showed a phylogenetic affinity of 99% with other isolates of P. aphanidermatum. According to the DI, the northern large and the long luffa genotypes were grouped as sensitive genotypes, and other genotypes including northern black seed, northern white seed, toori, Afghani, grooved and Brazilian were grouped as resistant genotypes. Based on the AUDPC, the northern black seed, and northern white seed genotypes showed the lowest level, toori, grooved, Afghani and Brazilian genotypes showed the medium level, and northern large and long luffa genotypes showed the highest AUDPC level. Conclusion: Considering the low values of the DI and AUDPC in the northern black seed and northern white seed genotypes, planting these two genotypes is suggested for management of the disease in luffa.
