Pollen Viability of Fraxinus excelsior in Storage Experiments and Investigations on the Potential Effect of Long-Range Transport

Fragmented ash populations due to ash dieback may lead to a limited gene flow and pollination success. Therefore, the viability of ash pollen plays a major role for the survival of the species. The extent to which the long-distance transport of pollen affects pollen viability was investigated with experiments in a climate chamber using ash pollen samples from a seed orchard in Emmendingen, Germany. Furthermore, experiments with a volumetric pollen trap were conducted. A suitable storage temperature for ash pollen was determined by using four viability tests; TTC test, pollen germination, Alexander's stain and Acetocarmine. An optimization of the germination medium was performed. We found a strong influence of prevailing temperatures on pollen viability, which decreased faster under warmer conditions. At moderate temperatures, viable pollen could still be observed after 28 days. Thus, a possible successful pollination can also be associated to long-range transported pollen. Storage experiments showed that pollen viability could be maintained longer at temperatures of -20 degrees C and -80 degrees C than at 4 degrees C. In particular, the TTC test has proven to be suitable for determining viability. Therefore, properly stored pollen can be used for breeding programs to support the survival of Fraxinus excelsior.

Automated summary

This study investigates the impact of long-distance transport on pollen viability in fragmented populations of ash trees affected by ash dieback. The viability of ash pollen is crucial for the survival of the species. The experiments conducted in a climate chamber and with a volumetric pollen trap show that prevailing temperatures have a significant influence on pollen viability, with warmer conditions causing faster decline. Optimal storage temperature and germination medium were determined, and properly stored pollen can be used for breeding programs to support the survival of Fraxinus excelsior.