Cytogenetic characterization of Hydrangea involucrata Sieb. and H. aspera D. Don complex (Hydrangeaceae): genetic, evolutional, and taxonomic implications

Abstract

The subsection Asperae of genus Hydrangea L. (Hydrangeaceae) has been investigated for three reasons: several ambiguous classifications concerning Hydrangea aspera have been published, unexpected differences in genome size among seven accessions have been reported Cerbah et al. (Theor Appl Genet 103:45-51, 2001), and two atypical chromosome numbers (2n=30 for Hydrangea involucrata and 2n=34 for H. aspera) have been found when all other species of the genus present 2n=36. Therefore, these two species and four subspecies of Hydrangea in all 29 accessions were analyzed for their genome size, chromosome number, and karyotype features. This investigation includes flow cytometric measurements of nuclear DNA content and bases composition (GC%), fluorochrome banding for detection of GC-and AT-rich DNA regions, and fluorescent in situ hybridisation (FISH) for chromosome mapping of 5 S and 18 S-5.8 S-26 S rDNA genes. In the H. aspera complex, the genome size ranged from 2.98 (subsp. sargentiana) to 4.67 pg/2C (subsp. aspera), an exceptional intraspecific variation of 1.57-fold. The mean base composition was 40.5% GC. Our report establishes the first karyotype for the species H. involucrata, and for the subspecies of H. aspera which indeed present different formulae, offering an element of discrimination. FISH and fluorochrome banding revealed the important differentiation between these two species (H. involucrata and H. aspera) and among four subspecies of the H. aspera complex. Our results are in agreement with the Chinese classification that places the groups Kawakami and Villosa as two different species: Hydrangea villosa Rehder and Hydrangea kawakami Hayata. This knowledge can contribute to effective germplasm management and horticultural use.

Pollen viability and meiotic behaviour in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group x subsp. sargentiana

“…sargentiana (clone 188), and their hybrids (Crespel et al 2012). Significant architectural differences were observed between these two subspecies and their hybrids in agreement with their level of genetic differentiation revealed both by cytogenetic and/or ISSR analysis (Mortreau et al 2010, Crespel et al 2012. These hybrids were of horticultural interest because of their plant habit and the shape of their inflorescences.…”

“…They can be attributed to chromosome pairing problems due to their lack of homology and are the expression of the typical behaviour of non-paired or univalent chromosomes. In addition to the different number of chromosomes (Cerbah et al 2001), Mortreau et al (2010) have shown significant differences in the chromosome organization between subsp. aspera Kawakami group and sargentiana, especially at the caryotypic level and that of the organization of heterochromatins and ribosomic sequences, confirming discrepancies between chromosomes and suspected pairing problems in our case.…”

“…The quantity of nuclear DNA and the ploidy level of the parents were previously assessed by Cerbah et al (2001) and Mortreau et al (2010) and are, respectively, equal to 4.67 pg/2C and 2n = 2x = 36 for Plant Breeding, 133, 536-541 (2014) …”

“…Because this method is difficult to implement, it was only used for three hybrids (H1, H2 and H3). Chromosomes were counted in squashed, actively growing root tips, as described by Mortreau et al (2010). Root tips were pretreated in a 0.025% colchicine solution for 24 h at 4°C, then fixed in a mixture of absolute alcohol and glacial acetic acid (3 : 1) and stored at 4°C.…”

“…McClint.) and has already been characterized both genetically and morphologically.In-depth genetic characterization was based on cytogenetic observations such as measurement of the quantity of nuclear DNA and karyotyping (Cerbah et al 2001, Mortreau et al 2010, as well as intersimple sequence repeats (ISSR) molecular markers (Mortreau et al 2003, Crespel et al 2012. To further understand genetic relationships within the H. aspera species complex, hybridizations were carried out, notably between the subsp.…”