关键词: 丁香属, 花粉形态, 花粉活力, 离体培养基, 贮藏温度, 繁育方式

Abstract:

Objective: The aim of this study is to clarify the pollen morphology and pollen germination methods in vitro of three Syringa species, compare the effects of different storage temperatures on pollen viability, and estimate the pollen/ovule ratio (P/O) and out crossing index (OCI), so as to provide reference for cross breeding of Syringa. Method: S. oblata, S. oblata var. alba and S. × persica were used as experimental materials, and the pollen morphology was observed using scanning electron microscopy. In vitro culture methods were used to study the suitable media for pollen germination, and the effect of different storage temperatures on pollen lifespan was explored. A blood cell counter method was used to calculate the P/O ratio and the out crossing index was estimated through measuring flower traits. Result: All three Syringa species had medium sized pollens, ellipsoidal in shape, with three germination grooves and clear network carvings. The ratio of pollen polar axis length to equatorial axis length (P/E) value ranged from 1.45 to 1.83, and the volume index ranged from 28.24 to 38.82. The contents of sucrose, boric acid, CaCl₂, GA₃, and 6-BA in the culture medium all had effects on pollen germination in vitro. The suitable medium composition for the pollen germination of three Syringa species was as follows: 15 g·L⁻¹ sucrose, 50 mg·L⁻¹ boric acid, 50 mg·L⁻¹ calcium chloride, and 25 mg·L⁻¹ 6-BA for S. oblate, 15 g·L⁻¹ sucrose + 50 mg·L⁻¹ boric acid + 50 mg·L⁻¹ calcium chloride + 50 mg·L⁻¹ GA₃ for S. oblata var. alba and S. × persica. Conclusion: According to the number, position and character (NPC) system of pollen classification, the pollen of all three Syringa species belongs to the N3P4C5-type, which can be identified based on pollen volume, P/E ratio, and extine pattern of pollen. The viability of pollens stored at room temperature can only be maintained for about 14 days. The pollens stored at –80 ℃ maintains high pollen viability, making it the optimal method for preserving pollens. The P/O ratio estimation suggests that the three Syringa species have outcrossing breeding system, whereas the OCI results suggest that the breeding modes of the three Syringa species are partial self-compatible, insect-pollination outcrossing.

Key words: Syringa, pollen morphology, pollen viability, in vitro germination medium, storage temperature, breeding mode