Genetic diversity assessment of a winter squash and pumpkin (Cucurbita maxima Duchesne) germplasm collection based on genomic Cucurbita-conserved SSR markers

- The genetic diversity study of Cucurbita maxima is reported.
- SSR markers developed for Cucurbita moschata and Cucurbita pepo were tested for C. maxima.
- A set of highly informative SSR markers for C. maxima genotyping was selected.
- C. maxima accessions were grouped according to the horticultural groups.

Molecular marker examinations of genetic diversity are valuable for assessment of within-species diversity and relationships, genotype identification, to assist selection for crop improvement programs, and to handle coherently germplasm collections. Cucurbita maxima is a highly diverse cucurbit crop, but its genetic diversity at the molecular level is inadequately characterized. Presently, genomic simple sequence repeat (SSR) markers that were described and employed for Cucurbita moschata and Cucurbita pepo were screened on C. maxima. A set of 23 highly informative SSRs was selected to evaluate genetic diversity within a collection of 85 C. maxima accessions. This collection contained cultivars and breeding lines from Europe, North America, Asia, Australia, and New Zealand, of six horticultural groups. Based on the genotyping results and statistical analyses, a fundamental division was observed in C. maxima above the level of horticultural groups. One major cluster was comprised between accessions from the Banana, Buttercup, and Hubbard horticultural groups. The other major cluster was divided in two sub-clusters, the larger of which included all accessions of the Mammoth (Show) Pumpkin horticultural group and the smaller, more outlying cluster was comprised of accessions of the Australian Blue horticultural group, with the one representative of the Turban group most outlying. Generally, the horticultural groups formed sub-sub-clusters, as most accessions within these respective groups showed close affinity. The selected set of 23 Cucurbita-conserved SSR markers is expected to be of great value for further germplasm characterization in this species and for taxonomical identifications within the genus Cucurbita.