Population Structure and Genetic Diversity in Cucurbita spp. Revealed by Microsatellite Markers

Understanding the genetic diversity and population structure of Cucurbita species is essential for effective germplasm conservation and the development of improved cultivars. This study aimed to evaluate the genetic diversity, population structure, and genetic relationships among accessions of C. pepo, C. moschata and C. maxima and their interspecific hybrids (Tetsukabuto hybrid C. maxima × C. moschata). A total of 92 accessions were analyzed using 22 polymorphic simple sequence repeat (SSR) markers selected from previous studies due to their high polymorphic information content (PIC). Genetic diversity parameters were estimated, and population structure was inferred using Bayesian clustering, complemented by dendrogram and principal component analysis (PCA). All markers were successfully amplified in C. pepo, C. moschata, C. maxima, and the hybrids, with polymorphic information content (PIC) values ranging from 0.191 (CMTm232) to 0.448 (CMTm48) and average of 0.274. The AMOVA analysis showed that 50% of the total variation was attributed to differences both within and among groups. PCA revealed clear genetic differentiation among the analyzed species, with C. maxima and hybrid accessions clustering closely and exhibiting lower genetic dissimilarity. In contrast, C. pepo displayed greater genetic divergence, supporting its distinct evolutionary trajectory. According STRUCTURE analysis the accessions can be divided into four subpopulations, which are closely related to the species. PCA and dendrogram showed similar results for genetic structure of Cucurbita germplasm; C. maxima and hybrid accessions clustering closely and C. pepo as a distinct group. These findings provide valuable insights for breeding programs, germplasm management, and conservation strategies aimed at preserving genetic diversity and exploiting interspecific variation.