The effect of pollination type on offspring vitality in small population of black poplar

Populus nigra L. is an ecologically important floodplain tree species whose declining and increasingly fragmented populations are exposed to the increased risk of inbreeding. This paper aimed to study mating processes that can occur in such populations. Offspring of mother trees with different levels of inbreeding and three types of pollination (inbred, outbred, and open pollination) were compared based on their vitality, assessed through seed germination and growth characteristics, over three consecutive years. Inbred crosses produced offspring that were the worst in most of the studied traits and in all observation years, demonstrating inbreeding depression. A negative association between inbreeding coefficients and the studied characteristics was confirmed in most cases. Parentage analysis of open-pollinated seedlings using eight microsatellite loci identified up to 49% of seedlings originating from spontaneous inbreeding of different levels. Moreover, pollen flow was predominantly short‑distance, with 66% of seedlings pollinated within 100 m of their maternal tree. These findings highlight the importance of maintaining genetic connectivity for the regeneration and long-term viability of black poplar populations.