Studies On Backcross Breeding Of F₁ Hybrids Between Primula Saxatilis And Primula Sieboldii

Primula species distant hybridization breeding is an important research direction of this genus of plants. Primula saxatilis, belonging to Sect. Cortusoides of Primula in Primulaceae, is included in the list of key protected wild plants in Beijing. It forms an umbel with 1-2 whorls of flowers which are small and loose. The corolla of P.saxatilis is purple red and the flower diameter can be up to 35mm. and the flowering period can last for more than three months. P.sieboldii, also belonging to Section Cortusoides of Primula in Primulaceae, has an umbel with 1 whorl of light red or purple red flowers which is tight and has a small flower diameter. And the flowering period of P.sieboldii lasts to around one month. To take full advantage of wild Primula resources and to combine the benefits of P.saxatilis and P.sieboldii and to obtain new Primula specie with large and tight flowers and also a long last flowering period, this research took the Fi generation of the hybrids of P.saxatilis and P.sieboldii as research object and used phenotypic evaluation and fertility evaluation on them. Based on the fertility evaluation, this research backcrossed by using F1 hybrids as female parent and the parent P.sieboldii as male parent to obtain F2 hybrids by embryo rescue technique. After that, the F2 hybrids were expanded and identified. Here are the main conclusions.1. After the phenotypic traits of 4 strains of P. saxatilis × P sieboldii F1 hybrids were evaluated and analyzed, it could be found that different hybrid plants showed consistency on phenotypic characteristics, which are significantly different from their parents. The Fi hybrids had tighter flowers than parents and showed characteristics of their parents on aspects of leaf shape, leaf margin, petiole color and flower eye. The hybrids’ flower diameter was 1.49-2.38cm which was between their two parents’, and the flowering period was earlier and longer than their male parents. SS-53 had a flowering period starting at early November and lasting to late February of the next year, while SS-18, SS-28 and SS-39’s flowering period lasted from early December to early February of the next year. P. saxatilis×P. sieboldii Fi hybrids showed some improvement characters on flower diameter and flowering period which made them could be used as the intermediate germ plasm to cultivate new target varieties.2. The fertility of P. saxatilis×P. sieboldii F1 hybrids was evaluated by observing pollen morphology feature and meaturing pollen viability and tigma receptivity. The results showed F1 hybrids’ anthers and pollen had serious abortion problem.4 lines of pollen germination rate were only 0%, 1.26%,0.76%, and 3.13% which meant they almost had no vitality and could not be used as male parents. The stigma of F1 hybrids had a certain degree of stigma receptivity which made them could be used as the female parents of further interspecific hybridization breeding.3. Backcross experiments were based on the results of fertility evalution.4 different type of pollination backcross combination were set up and 380 flowers were pollinated, there was a certain degree of enlargement on ovaries from each combination, which is positively correlated with the stigma receptivity of the female parents.But the ovaries all got abortion within 35-42 days after pollination and seeds cannot be naturaly produced which means there is a serious reproductive isolation.37-40 days after pollination is an appropriate embryo rescuing time for the hybrids with short style Fi as female parents and P. saxatilis as male parents.4. Having P. saxatilis×P. sieboldii Fi hybrids as female parents and P. saxatilis as male parents, 154 ovaries with almost 8000 ovules were rescued and ten of the ovules germinated.7 plants of F2 hybrids were obtained by embryo rescuing. SSR molecular identification technique was used to 4 strains of F2 hybrids. Combining the morphological features, backcross-3 and backcross-5 could be substantially identified as true hybrids while backcross-1 and backcross-7 need further identifications.This research made full use of endangered wild P.saxatilis to obtain backcross generation with F1 hybrids of P.saxatilis and P.sieboldii as female parent and P.sieboldii as male parent and laid the foundation for cultivating new Primula species with large flowers, compact inflorescence and long flowering period.