The use of grafted seedlings in Cucurbits has increased in recent years as interspecific hybrids between Cucurbita maxima Duch. and Cucurbita moschata Duch. have become the preferred rootstock for watermelon, melon and cucumber. The interspecific hybrid seed production of C. maxima x C. moschata mainly depends on genotype compatibility. In this study, different interspecific hybridization combinations were evaluated in order to obtain C. maxima x C. moschata rootstocks. The field experiment of this study was carried out in the Carsamba district of Samsun Province in 2009. The initial genetic materials were inbred and purified up to the Ss generation. These genotypes were selected based on plant vigor, hypocotyls characteristics and seed yields. A total of 234 pollinations of different combinations between twelve C. maxima lines and eleven C. moschata lines were performed. 79 interspecific hybrid fruits were obtained from these hybridizations. Crossing incompatibility was found to be highest in the MO8 lines (C. moschata) in all combinations. The MA4, MA9 and MA12 winter squash (C. maxima) lines were determined to be promising ones for obtaining hybrid seed yield. In conclusion, the MA9 x MO8, MA12 x MO2 and MA4 x MO8 hybrid combinations were the most promising candidates for rootstock breeding. As a result of this study, these selected combinations will be used in the development of promising new rootstock cultivars. (C) 2012 Elsevier B.V. All rights reserved.