Genetic structure of the pine needle pathogen Lecanosticta acicola in Lithuania and northern Poland

Abstract

AbstractBrown spot needle blight, a disease of pine trees caused by the pathogenic fungus Lecanosticta acicola, has been known in Lithuania since 2009 and in Poland since 2014, but data on the distribution and population genetics of this needle pathogen were lacking. In order to investigate the genetic diversity, population structure and reproductive mode of L. acicola, 93 isolates were isolated from Pinus mugo needles in 2017–2019 and analysed using 11 microsatellite and two mating‐type markers. This study revealed 47 unique multilocus haplotypes among all investigated isolates; two genetically distinct populations of L. acicola (LIT‐E and LIT‐W) were identified in Lithuania and one population (POL‐N) in the coastal region of northern Poland. The most genetically diverse population was the LIT‐E population occurring in the eastern continental part of Lithuania, followed by the LIT‐W population spreading along the western Baltic Sea coast. All populations in both countries are characterized by low genetic diversity and contain clones, with the northern Polish population having the lowest mean genetic diversity and the greatest clonal fraction. Both mating types are present in the Lithuanian populations, demonstrating that sexual reproduction is possible, whereas only one mating type is present in the Polish population. However, the sexual stage (teleomorph) has not yet been found on infected needles, and asexual reproduction predominates. High gene flow from the eastern Lithuanian population to the northern Poland population was found, suggesting that the Polish coastal population may have been introduced from the central part of Lithuania and did not spread naturally along the Baltic Sea coast from the western Lithuanian population.