Introduction: Awareness of the extent of genetic diversity based on molecular markers is a rapid method that plays an important role in breeding programs. Cucumis melo L. is the scientific name for a melon that belongs to the Cucurbitaceae family (Kirkbride, 1993). This plant is a popular garden crop in warm and temperate climates across the globe, and Iran ranks fourth in the world in terms of output (FAOSTAT, 2019). Although several studies were conducted on the genetic structure of Iranian melons using various molecular markers including RAPD molecular markers (Feizian, 2004), ISSR (Maleki et al., 2018) and SSR microsatellite markers (Moayedi Nejad et al., 2010; Raghami et al., 2014) in recent years, due to the history of planting and the presence of huge genetic resources of melon, which makes Iran as one of the main centers of diversity of this crop in the world, research is inadequate.
Materials and Methods: Forty native melon stands used in this research were prepared from the melon germplasm of Iran Gene Bank. 4-5 leaves from each plant at the two- to three-leaf stage were collected and kept in a freezer at -80°C until DNA extraction. Their genomic DNA was extracted using the ZandBio plant kit. The markers used in this research were selected based on previous studies that were suggested by different researchers. Gradient PCR Vapo Protect thermocycler was used for polymerase chain reaction. PCR products were electrophoresed on 1.8% agarose gel in 1X TBE buffer and at 85 V for one hour. Observation and photographing of the gel was done with the help of UV-2100 geldoc device. Bands were scored as zero (not seeing a band) and one (observing a band). Evaluation of cluster analysis and genetic parameters such as observed heterozygosity, expected heterozygosity and number of effective alleles were obtained through Ntsys 2.1 and Popgene 1.32 software. To estimate the number of subpopulations (K) and distinguish pure and mixed genotypes, it was done using Structure software version 2.3 and using the Bayesian method (Pritchard et al., 2000).
Results and Discussion: All gene loci except CMCT44 primer were polymorphic. A total of 25 alleles with an average of 1.93 alleles per microsatellite gene locus were observed. The highest amount of polymorphic sites (84.62%) belonged to KC-357009 genotype.. The high amount of polymorphic sites confirms the effectiveness of SSR molecular markers in the genetic analysis of the investigated indigenous populations. The average content of polymorphism and expected heterozygosity information was obtained as 0.24 and 0.23, respectively. The observed high homozygosity values with an average of 0.84 indicate the low diversity within the investigated populations, which is a proof of the low level of variation between the populations and the high level of inbreeding. In the investigation of the genetic structure of the populations, the investigated populations were divided into two groups (sub-populations). The results of population structure analysis based on Bayesian method and UPGMA clustering showed that the classification of studied genotypes is independent of their geographical origin.
Conclusion: According to the values obtained from the above parameters, among the studied primers, gene locations CMCCA145, CMGA172 and CMCT134b are recommended for the analysis of melon germplasm collections in future research.
The results of this study can be used in hybridization programs. Crossing between the figures that have the least similarity will lead to the best results in achieving hybrids or achieving maximum separation in the generations after F1. Although genetic distance is not the only effective factor in identifying suitable parents for hybrid production and factors such as compatibility and genetic distance based on morphological traits should also be considered.