Patterns of genetic diversity resulting from bottlenecks in European black pine, with implications on local genetic conservation and management practices in Bulgaria

In the present study, we investigated the genetic structure and diversity of P. nigra populations in Bulgaria, using simple sequence nuclear repeats. Among-population structure was studied with distance and Bayesian frequency methods, assuming geometric distance and a “non-admixture” model. The “NJ” and “non-admixture” clusters confirm the “mountain effect” hypothesis of the black pine genetic structure in the study region. The analyses showed moderate among-population divergence (13.31 %; AMOVA) and evidence of genetic bottlenecks. The coalescent analyses suggest that P. nigra has survived for a long period (thousands of generations) under strong selection pressure and that its populations continued to be exposed to stochastic factors like climate fluctuation, forest fire and disease. The combination of recent and historic changes is responsible for the present population size and genetic diversity. Our results suggest that conservation and management practices should strive to maintain this genetic differentiation, specifically by emphasising reforestation efforts with stocks from local provenances to avoid non-local introductions.