Pollen viability and fertility assessment in range edge populations of Alnus glutinosa (L.) Gaertn

Alnus glutinosa (L.) Gaertn is a crucial component of riparian ecosystems. Yet, many of its habitats are currently under threat, particularly in the southern regions of its distribution in Morocco. To effectively address the conservation and management of this species, it is imperative to gain a comprehensive understanding of various aspects of the species’ reproductive biology. The main objective of this study was to assess the viability and fertility of Alnus glutinosa (L.) Gaertn pollen grains using four tests: acetocarmine staining, Alexander staining, 2.3.5-triphenyltetrazolium chloride (TTC), and in vitro germination. Eleven representative populations of this species were carefully selected for analysis. The study revealed that Alnus glutinosa trees produce pollen with good cytoplasmic conformation, as exhibited by the acetocarmine (86.4%) and Alexander staining (74.45%). However, these tests tend to overestimate pollen viability, as estimates by the TTC enzymatic test (48.88%) and in vitro germination (4.5%) are significantly lower. Viability varied significantly both among and within populations. The results suggest that some trees produce sterile pollen. The observed variability in pollen viability between populations appears to be linked to environmental factors.