Rapid identification of inflorescence type markers by genotyping-by-sequencing of diploid and triploid F1 plants of Hydrangea macrophylla

Abstract

Background The ornamental crop Hydrangea macrophylla develops highly attractive lacecap (wild type) or mophead inflorescences. The mophead trait, which is mostly favored by consumers, is recessively inherited by the INFLORESCENCE TYPE locus ( INF ). If lacecap cultivars are crossed with mophead cultivars, then either 50% or all progenies develop lacecap inflorescences, depending on the zygosity at the INF locus. For most cultivars, the zygosity at the INF locus is unknown. Furthermore, the determination of the inflorescence type in offspring populations is time-consuming, because seedlings flower the first time in the 2nd year after sowing. Within this study, we aimed to develop DNA-based markers that allow to determine the zygosity at the INF locus of prospective parental plants and to predict the inflorescence phenotype of seedlings already in the non-flowering stage. Results By crossing a mophead and a lacecap cultivar of H. macrophylla , we produced a pseudo-backcross F 1 population consisting of 422 plants. These plants segregated into 279 lacecap, 73 mophead, 3 intermediate and 67 non-flowering plants, differing significantly from the expected 1:1 segregation ratio. Surprisingly, 75% of these plants were triploid, although both parents were diploid. We found that the lacecap parent produced unreduced pollen, which induced the formation of triploids. 380 randomly selected F 1 plants were genotyped by genotyping-by-sequencing (GbS). Using a genome assembly of cultivar ‘Sir Joseph Banks’, we performed subsequently a bulk sequence analysis with pooled GbS data of diploid versus mophead plants. We identified directly 2 markers tightly linked with the INF locus, each of them explaining 99.7% of the inflorescence phenotype. Using a collection consisting of 56 diploid, triploid or tetraploid H. macrophylla varieties, we detected 6 sequence variants for one of these markers. Two variants were associated with the mophead phenotype. Furthermore, we found by marker analysis a co-segregation between the mophead and the non-flowering trait, which indicates a major flowering time locus next to the INF locus. Conclusion Through bulk sequence analysis of pooled GbS data from diploid and polyploid F 1 plants, we identify rapidly tightly linked markers for the inflorescence type, a dominant-recessively inherited trait in the non-model plant species H. macrophylla . Electronic supplementary material The online version of this article (10.1186/s12863-019-0764-6) contains supplementary material, which is available to authorized users.

Targeted generation of polyploids in Hydrangea macrophylla through cross-based breeding

“…In contrast, triploid plants have 2n = 3x = 54 chromosomes, and 2C DNA contents vary between 6.5 and 7.3 pg [6][7][8][9][10][11]. Recently, a cultivar has been found with a 2C DNA content of 8.9 pg, suggesting tetraploidy [12]. About 30 triploid cultivars were reported until now [7][8][9][10].…”

Genome-wide association studies for inflorescence type and remontancy in Hydrangea macrophylla

“…Also, the F1 population may have contained triploids due to unreduced gamete formation in the parents 45 . The presence of triploids in an F1 population has been linked to skewed segregation ratios 46 . Finally, the mismatch of genotype and phenotype could be due to the basic methodology of GBS.…”

“…An insertion of a long terminal repeat retrotransposon into the locus controlling inflorescence type was also proposed by the same research group through an observation of lacecap hydrangea cultivar mutation, but such a finding was not able to be connected to the current study due to limited genomic information. While genetic markers linked to inflorescence type in bigleaf hydrangea have been reported previously 46,50 , the single marker discovered and utilized herein has advantages for use in MAS. The previously published markers must be used in combination for marker-assisted selection while the SNP detailed here can be used alone.…”

Ploidy Level Influences Pollen Tube Growth and Seed Viability in Interploidy Crosses of Hydrangea macrophylla

“…Sympatry of different ploidy levels primarily arises through repeated formation of unreduced gametes by diploids (primary origin) or from secondary contact between previously allopatric diploid and polyploid populations (secondary origin; Petit et al, 1999). H. macrophylla shows both high rates of 2n gamete formation (Tränkner et al, 2019) and weak internal pre-zygotic reproductive barriers between ploidy levels as both diploids and triploids are nearly identical with respect to morphology, phenology, and likely habitat preferences (McClintock, 1957). The current study provides insight into a potential pre-zygotic barrier relating to pollen tube growth, where tubes of pollen from triploid parents grew more slowly than tubes of pollen from diploid parents, regardless of the ploidy level of the female parent.…”

“…macrophylla. An F1 mapping population from two diploid parents contained 103 diploids and 317 triploids (Tränkner et al, 2019). Alexander (2017) showed that controlled crosses using a cultivar known to produce unreduced male gametes resulted in 97% triploid offspring in the progeny.…”