Effect of temperature on pollen germination and pollen tube growth in longan (Dimocarpus longan Lour.)

- Optimization of a method for longan pollen storage and pollen germination in vitro.
- Determination of the best temperature regime for in vivo pollen germination.
- Differential effect of temperature on pollen germination and pollen tube growth depending on the cultivar.

ABSTRACTLongan (Dimocarpus longan) is a subtropical fruit tree with a long cultivation tradition in South East Asia, and also with a clear potential in other areas of the world. In other plant species, the reproductive phase is most vulnerable to temperature conditions, but information on the effect of temperature on pollen germination and tube growth in longan is still lacking. In order to fill this gap, in this work the effect of temperature on longan pollen germination was assessed both in vivo and in vitro. For this purpose first pollen germination was evaluated in vivo at three temperature regimes, showing the best performance at 23/24 °C. Then an in vitro pollen germination medium was optimized for longan and pollen storage conditions were evaluated, showing good pollen germination in vitro after storage for one year at −20 °C. Finally, the effect of temperature was evaluated in vitro in four cultivars and for two male flower types M1 and M2, differing on the degree of pistil differentiation. Both pollen types behave similarly in all conditions, and all the cultivars studied had good pollen germination in vitro at 30 °C, a temperature higher than that reported as optimum in vivo reflecting a higher sensitivity of the stigma than pollen to high temperatures. However, clear differences between cultivars in their performance at 20 °C and 40 °C were recorded. These results set the basis for reproductive biology studies and breeding in longan, opening a window to select the best cultivars for different temperature conditions.