Effect of high temperature on the production of 2n pollen grains in diploid roses and obtaining tetraploids via unilateral polyploidization

Abstract

To integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high-temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest. Key words: 2n gametesRose is the most economically important ornamental crop worldwide because of its popularity as a garden, landscape and potted plant, and as cut flower (Gudin 2000). The genus Rosa subgenus Rosa comprises ten sections and more than 200 species (Wissemann 2003, Foug ere-Danezan et al. 2015. Ma€ ıa and Venard (1976) and Berninger (1992) showed that <10 species belonging to three sections are at the origin of roses (Rosa hybrida L.) cultivated today. Many cultivated roses are tetraploid (2n = 4x = 28), whereas many wild species are generally diploid (2n = 2x = 14).Rose breeders have attempted to enrich the variability of the gene pool of cultivated roses by introducing germplasm of new diploid wild species. Many interspecific hybridizations between tetraploid rose cultivars and wild diploid species were carried out, but produced triploids that were generally sterile, making it very difficult to generate additional generations (Wylie 1955). To integrate the variability of diploid species into the gene pool of cultivated roses, a haploidization programme of cultivated roses was developed in the 1990s by Meynet et al. (1994) that consisted of reducing the ploidy level of cultivated rose from tetraploid to diploid. This programme involved three steps: (i) producing dihaploids (diploid) from tetraploid rose cultivars, (ii) creating progeny of interspecific diploid hybrids developed by crossing dihaploid cultivated rose cultivars with wild diploid species and (iii) returning to the tetraploid level (ploidy level most frequently encountered in the cultivated rose) (Crespel and Meynet 2003).Only the first two steps of this programme were carried out. Dihaploids of tetraploid rose cultivars were obtained by parthenogenesis in situ induced by irradiated pollen and immature embryo rescue techniques in vitro (Meynet et al. 1994). The study of their gametogenesis revealed different meiotic anomalies such as abnormal spind...

The strong competitive role of 2n pollen in several polyploidy hybridizations in Rosa hybrida

“…High heterozygosity of the FDR-type gametes determines their ability to transfer parent heterozygosity and epistatic efficiently, and therefore have a higher utilization value in breeding. The production of 2n pollen based on a series of meiosis observations that focused on FDR-types was previously discussed, including the cellular processes of the dyad products of the parallel spindles and the triad products of the vertical spindles [29, 31, 34]. The hybridization offspring of two lily cultivars ( L. auratum × L. henryi ) produced a number of 2n gametes and were crossed with another lily hybrid (the Oriental hybrid) to produce triploid offspring [40].…”

“…As a successive type of meiosis, potatoes produce normal dyads, and chromosome bridges and lagging chromosomes were found in anaphase I and II [52]. A parallel spindle resulted in abnormal meiosis in rose [29, 34], whereas other studies suggest that the parallel spindle is a common process in the formation of normal tetrads, and a fused spindle indicates abnormal meiosis [53]. In our study, the fusion spindle and the triple spindle developed from the vertical spindle, and thus it was proposed that the 2n pollen was mainly generated from two abnormal division methods in rose.…”

“…The 2n pollen of ‘Old Blush’ was identified using the method of Crespel et al [29]. Briefly, the pollen diameters were measured after Alexander staining under the microscope, and more than 500 pollen grains were measured for each sample.…”

“…The diploid species R. wichurana produced 2n pollen in the ratio of 1.10~24.50% under various high temperature treatments and exhibited specific morphological variation in the amount of colpis and ectexine deposition, resulting in less striated structures as observed by scanning electron microscopy [28]. High temperatures led to increases in the number of 2n pollen from the diploid rose ‘HW154’, with the probability of dyads, triads, or polyads ranging from 0 to 6.20%, and 40 tetraploid hybrids among the 95 offsprings which generated from the crosses of diploid male parents with tetraploid female parents and analyzed by flow cytometry [29].…”

Flow cytometry – a modern method for exploring genome size and nuclear DNA synthesis in horticultural and medicinal plant species

“…Polyploids (usually tetraploids) are most often obtained in vitro or ex vitro by treatment with an antimitotic agent, and plants of desirable ploidy are selected using FCM. This approach was successfully performed for 3 Hibiscus species, Rhododendron hybrid R. × kosterianum, Syringa vulgaris × S. pinnatifolia, a few Rosa species, Gerbera jamesonii, Hemerocallis × hybrida, and Petunia axillaris (Rose et al, 2000;Väinölä, 2000;Van Huylenbroeck et al, 2000;Allum et al, 2007;Crespel et al, 2015;Podwyszyńska et al, 2015;Regalado et al, 2017). The induction of artificial polyploidy can also increase the production of important medicinal compounds and for this reason was introduced into Ocimum basilicum, Thymus persicus, and Trachyspermum ammi (Omidbaigi et al, 2010;Tavan et al, 2015;Noori et al, 2017).…”