Abstract:【Objective】During crossbreeding, there are problems of asynchronous flowering and long-distance hybridization. Pollen storage, which can keep its viability within a period of time, can help overcome the temporal and spatial barriers and solve parental selection problem, contributing a lot to success in the process of crossbreeding. Studies had shown that besides pollen genetic factors, pollen viability is also determined by external environment: low temperature, low relative humidity, low pressure, especially vacuum conditions can be help extend the pollen storage time. Many previous studies probed into plant pollen storage; however, no much attention had been paid to research on pollen storage of carambola fruit trees that is of small quantity in southern China, with only nutrient composition, scanning electron microscopy (SEM) observation and in vitro germination formula of carambola pollen reported. In this study, carambola pollen preservation methods were investigated to provide a theoretical basis for carambola pollen storage and carambola crossbreeding. 【Methods】"Hawaii" carambola, introduced from Hawaii, the United States, has light yellow flesh, sweet flavor, less pomace and ample juice, showing excellent quality. A study found that "Hawaii", with strong fresh pollen viability and resistance during pollen germination could be a good male material for crossbreeding. This study took "Hawaiian" carambola as the experimental material. In the morning, the well-developed flowers that opened that day were picked, and the anthers were taken and wrapped with sulphate paper. The pollen was dried and vacuumed. Drying treatment: put the pollen into 50 mL frozen storage tube and fill it with silica gel desiccant. Vacuum treatment: The pollen is packed into a bag and vacuumed with a vacuum machine (MeGIS MS1160). Untreated pollen was used as CK. The dried, vacuumed and control samples were stored in incubators at 25 ℃ and refrigerators at 4 ℃, -20 ℃ and -40 ℃, respectively. Pollen germination rate and pollen tube length were measured at 0, 3, 7, 15, 30 and 90 d of storage. 【Results】The germination rate of pollen preserved at 25 ℃ were 12.12% and 9.57%, respectively, and those preserved at -40 ℃ were 35.68% and 32.59%, respectively. The germination rate of pollen preserved at 25 ℃ for 10 d was 0, while that of pollen preserved at -40 ℃ for 90 d was over 50%, indicating that low temperature could effectively prolong the viability of carambola pollen. The germination rate of pollen dried by silica gel and CK was 0 at different temperatures for 3 d, indicating that silica gel desiccant had no significant effect on carambola pollen storage. The germination rate of vacuumed carambola pollen was nearly 20% when stored at 25 ℃ for 7 d; the viability of the pollen stored at -40 ℃ for 90 d was more than 50%; the germination rate of the pollen treated without vacuum was 0 when stored at all temperatures for 3 d, indicating that vacuum treatment is an important factor in the effective storage of carambola pollen. In summary, the combination of vacuum treatment and low temperature (-20 ℃ or -40 ℃) can effectively help store carambola pollen. 【Conclusion】At 25 ℃ and 4 ℃, both silica gel desiccant and vacuum treatments are not suitable for long-term carambola pollen preservation. At -20 ℃ and -40 ℃, silica gel desiccant treatment is not suitable for long-term carambola pollen preservation, and vacuum treatment can effectively preserve carambola pollen for up to 90 d. Both vacuum and low temperature can effectively extend the storage period of carambola pollen.
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