Karyotyping of commercial cultivars of melon (Cucumis melo L.)

Background This study on cultivars of melon (Cucumis melo L.) marketed in Brazil was conducted to obtain information to be used in breeding programs of this species. Little is known about the karyotype variability among C. melo L. cultivars targeted at the consumer market. The objective of the present study was to verify the karyotype variability in eight commercial melon cultivars used in the Brazilian market. Methods and results Slides were stained with 2% Giemsa and assembled with Neomount to perform chromosomal morphometry. GC-rich heterochromatin was observed by CMA(3)/DAPI staining. 5 S rDNA, centromeric satellite DNA (SatDNA), and telomeric sites were visualized using fluorescence in situ hybridization. All images were captured on an Olympus BX41 microscope equipped with a 5 M Olympus DP25 digital camera and DP2-BSW software. The cultivars showed symmetrical karyotypes with significant differences in total chromosome length and average chromosome size. Heterochromatic CMA(3)(+) blocks were observed in terminal regions related to satellites (secondary constrictions), as well as in centromeric and pericentromeric regions. A single chromosomal pair of 5 S rDNA sites was observed in all cultivars, but at distinct locations. Centromeric satellite sequences, tested for the first time in melon, revealed only centromeric sites. Telomeric sites were observed in all the chromosomes of the cultivars. Conclusions Karyotype variation was observed in cultivars of melon, which were analyzed for chromosomal morphology and localization of GC-rich heterochromatin, as well centromeric SatDNA, rDNA, and telomeric chromosomal markers. Hence, these cultivars can be used in future breeding programs.