Karyotypic characterization of melon accessions

Abstract

Cucumis melo (melon) is a species from the Iberian Peninsula and is included in the family Cucurbitaceae. Despite the knowledge about the physical structure of melon chromosomes, little is known about the intraspecific karyotype diversity of the species. To study karyotype diversity in eight melon accessions, the following methods were used: Giemsa 3% staining; application of CMA3/DAPI fluorochromes; and location of 45S and 5S rDNA sequences by fluorescence in situ hybridization. Conventional staining analysis revealed stability in the chromosome number, with accessions presenting 2n = 24. There were significant variations in the mean chromosome size between accessions, ranging from 0.98 μm to 1.46 μm for accessions A26 and A18, respectively. Scott-Knott clustering distributed the accessions into two groups. GC-rich heterochromatic blocks (CMA3 + /DAPI-) were observed in pericentromeric regions of all chromosomes in the complement. CMA3 + /DAPIblocks were also located in terminal regions, being specific to satellite regions. Hybridization sites of 45S rDNA probes revealed the presence of a chromosome pair with this locus. In addition, 5S rDNA sites revealed a labeled chromosome pair. No quantitative variation was observed in rDNA sites between the accessions analyzed, indicating these markers as ideal for the verification of karyotypic stability in C. melo.

Chromomycin A3 banding and chromosomal mapping of 45S and 5S ribosomal RNA genes in bottle gourd

“…Chromosomes stained with CMA 3 revealed four bands in terminal regions of chromosomes in this species. Our results of CMA 3 /DAPI staining are in line with those obtained by Lombello and Pinto-Maglio, (2007) and Santos-Sanchês et al, (2019).…”

“…Also FISH with the 45S rDNA probe yielded four signals. In plants, 45S rDNA loci and CMA 3 positive heterochromatic blocks often coincide spatially (Lombello and Pinto-Maglio, 2007;Maragheh et al, 2019;Santos-Sanchês et al, 2019). 5S rDNA sites were not detected by CMA 3 /DAPI banding.…”

“…They found no band on the chromosomes with DAPI staining. Santos-Sanchês et al, (2019) conducted similar work on different melon accessions and reported a DAPI positive band on the metaphase chromosomes. Chromosomes stained with CMA 3 revealed four bands in terminal regions of chromosomes in this species.…”

“…The 5S rDNA genes consist of a nontranscribed spacer and a conserved coding region of 120 bp (Long and Dawid, 1980). 45S and 5S rDNA genes can be present at one or more positions within a set of chromosomes and be used as chromosomal markers (Long and Dawid, 1980;Lombello and Pinto-Maglio, 2007;Han et al, 2008;Heslop-Harrison and Schwarzacher, 2011;Li et al, 2016;Santos-Sanchês et al, 2019). CMA 3 (chromomycin A3), a GC-rich specific fluorochrome, and DAPI (4'-6-diamidino-2-phenylindole), an AT-rich specific fluorochrome, banding techniques can also be useful to differentiate between chromosomes (Kim et al 2002).…”