Cytogenetic variation among Cucumis accessions revealed by fluorescence in situ hybridization using ribosomal RNA genes as the probes

抄録

Cucumis melo, one of the most important horticultural crops in Cucumis genus, has great variation in fruit sizes and shapes. Although comparative karyotype in Cucumis species has been conducted by several researchers, detailed information on molecular cytogenetic variation in relation to centromeres and ribosomal DNA (rDNA) loci within C. melo groups and other Cucumis species are still limited. Here, we conducted physical mapping of centromeric DNA (Cmcent), and two rDNAs (5S and 45S) on C. metuliferus, C. hystrix, and nineteen accessions of C. melo that were classified into subspecies melo and agrestis. Fluorescence in situ hybridization (FISH) using 5S and 45S rDNA probes revealed cytogenetic variation among C. melo accessions. C. melo subsp. melo and agrestis showed high conservation in terms of the number of 5S and 45S rDNA loci. However, the 45S rDNA signal intensities and the 5S rDNA locations are variable among C. melo species tested. Most of the accessions in agrestis group had two pairs of 45S rDNA with similar FISH signal intensities, except P90. Great variations were observed in melo group where some of the accessions showed similar patterns to subsp. agrestis while others showed two pairs of 45S rDNA loci with variable signal intensities. Our findings provide useful information for distinguishing C. melo accessions using centromeric DNA and rDNA probes, which would be important for breeding programs in melon.