Effects of two storage methods on pollen viability of Carambola (Averrhoa carambola L.) under different temperature conditions

Abstract:【Objective】During crossbreeding, there are problems of asynchronous flowering and longdistance hybridization. Pollen storage, which keeps its viability for a period of time, helps to overcome the temporal and spatial barriers and enables free parental selection, contributing a lot to success in crossbreeding. Studies have shown that besides pollen genetic factors, pollen viability is also determined by external factors including low temperature, low relative humidity and low pressure. Vacuum conditions can help to extend the pollen storage time. Although there have been many studies probing into plant pollen storage, not much attention have been paid upon the storage of pollen of carambola, which is a minor fruit crop produced in southern China. There have been some studies related to nutrient composition, scanning electron microscopy (SEM) observation and in vitro germination of carambola pollen. In this study, carambola pollen preservation methods were investigated for storage of carambola pollen for crossbreeding.【Methods】“Hawaii”carambola, introduced from Hawaii, has light yellow flesh, sweet flavor, less pomace, ample juice and excellent quality. A previous study found that fresh“Hawaii”pollen had high viability and resistance and could be a good pollen parent for cross-breeding. This study used“Hawaiian”carambola as the experimental material. Well-developed flowers were collected in the morning, and their anthers were taken and wrapped with sulphate paper. For drying treatment, the pollen grains were put into 50 mL frozen storage tube and filled with silica gel desiccant. For vacuum treatment, pollen grains were packed in a bag and vacuumed with a vacuuming machine (MeGIS MS1160). Pollen grains without drying and vacuum treatment were used as the control (CK). The dried, vacuumed and control samples were stored in incubators at 25 ℃ or in refrigerators at 4 ℃, -20 ℃ or -40 ℃. Pollen germination rate and pollen tube length were measured at 0, 3, 7, 15, 30 and 90 d of storage.【Results】In the drying treatment and control, the germination rates of pollen preserved at 25 ℃ for 1 day were 12.12% and 9.57%, respectively, and those preserved at -40 ℃ for 1 day were 35.68% and 32.59%, respectively. The germination rate of pollen preserved at 25 ℃ for 10 d was 0 in vacuum treatment, 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 rates of pollen in drying treatment and control were 0 under 25 ℃ for 3 day, 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 was 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 improve storage of carambola pollen.【Conclusion】At 25 ℃ and 4 ℃, both silica gel desiccant and vacuum treatments fail to prolong carambola pollen preservation. At - 20 ℃ and -40 ℃, silica gel desiccant treatment does not help long-term carambola pollen preservation, while 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.