Architectural and genetic characterization of Hydrangea aspera subsp. aspera Kawakami group, H. aspera subsp. sargentiana and their hybrids

Abstract

Hydrangea macrophylla (Thunb.) Ser. and H. paniculata Sieb. are the two most economically important species within the genus Hydrangea, and have been used as ornamental garden plants for a long time. However, other species such as H. aspera D. Don are of horticultural interest, particularly for the color of their inflorescences and plant shape. This species is composed of four sub-species and has previously been characterized both genetically and morphologically. The previous morphological characterization was qualitative, but was based mainly on leaf and inflorescence parameters outlined by UPOV, and provided little information about plant shape. To better characterize the shape of H. aspera, an architectural analysis was applied to the two most distantly related sub-species at the cytogenetic level:subsp. sargentiana (Redher) E.M. McClint. (clone 188) and subsp. aspera Kawakami group (clone 352). This method made it possible to reveal significant differences between these clones, both at the axis and the growth unit (GU) scale, in agreement with the high level of genetic differentiation (Jaccard dissimilarity index equal to 0.97) revealed between the two clones by Inter simple sequence repeats markers. Because this method is difficult to apply to a large population of individuals, a qualitative architectural characterization was tested on ten progenies derived from hybridization of the two clones, on the basis of their most discriminating architectural components. The hybrid nature of the progeny was confirmed by the architectural analysis. The architectural components of the hybrids are therefore a combination of those of the parents, with a predominance of clone 352, the female parent. Architectural differences between hybrids were clearly revealed by the length of the first vegetative GU (VGU1), the presence or the absence of VGU2 and the length of the floral GU of the A2 axis, and GU branching, allowing us to define five architectural profiles. These differences are supported by the average Jaccard dissimilarity index (0.33). This method, based on a qualitative description of the main architectural components of the plant, proved to be useful for characterizing the shape of H. aspera subsp. sargentiana, and subsp. aspera Kawakami group, and their hybrids. It could be extended to other sub-species of H. aspera and to their respective hybrids, providing an efficient L. Crespel (

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

“…aspera Kawakami group (clone 352) and subsp. 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.…”

“…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 architectural and ISSR analysis recently applied to these two subspecies support the high level of genetic differentiation revealed by cytogenetic observations (Crespel et al 2012). Assumed reductions in association and abnormal chromosome distribution produce unbalanced and generally sterile pollen grains.…”

“…It was confirmed in the hybrids H1, H2 and H3 by counting chromosome in this study. The relative quantity of nuclear DNA of hybrids H4 to H10 is within the range of hybrid values H1 to H3 (Crespel et al 2012); their ploidy level can therefore be estimated at 2n = 2x = 35.…”

“…aspera Kawakami group (clone 352) and subsp. sargentiana (clone 188) was determined beforehand by ISSR profiling and relative quantification of nuclear DNA (Crespel et al 2012). The relative quantities of nuclear DNA of hybrids were intermediate to that of the parents; their ploidy level should therefore be equal to 2n = 2x = 35.…”

“…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.…”