Characterization of the mycobiome of Pinus sylvestris L. seedlings damaged by forest animals, with an emphasis on pathogenic species

In Poland, red deer, roe deer and elk cause great damage to pine stands, and pine is the predominant forest-forming tree species in Polish forests. Pine seedlings planted adjacent to agricultural fields face heightened risk of damage from nocturnal foraging by game animals, which retreat to forested areas during the day. This damage creates openings for fungal entry, particularly by concerning plant pathogens, such as Fusarium species, which are prevalent in agricultural settings. This study aimed to analyze the mycobiome of pine seedlings damaged by forest animals, focusing on the presence of concerning pathogens in infested pine seedlings collected from ten forest plantations at various distances from rural areas. Samples of pine seedlings bitten by forest animals were taken from 10 forest plantations at different distances from rural areas. Selected diversity indices were determined to compare the fungal populations. Mycological analysis of the gnawed pine shoots using culture and qPCR methods revealed 746 fungal colonies. The most frequently isolated species were: Fusarium avenaceum, Alternaria alternata, Botrytis sp., Cladosporium cladosporioides, representatives of the genus Penicillium, Rhizopus nigricans and Fusarium oxysporum, which were found in samples from all study plots and are thus ubiquitous. Species that are typical pathogens of agricultural crops, such as Fusarium avenaceum, F. culmorum, F. poae, F. sporotrichioides and F. tricinctum, were also isolated from damaged seedling tissue in forest plantations neighbouring agricultural fields. Spearman’s rank correlation analysis showed that the importance of secondary pathogens, represented by species of the genus Fusarium, decreased with increasing distance from agricultural fields, while the importance of primary pathogens increased. Younger pine seedlings exhibited lower species diversity and a higher prevalence of specific secondary pathogen species, coupled with heightened susceptibility to infection compared to older seedlings when subjected to tissue damage by forest animals. These findings underscore not only variations among plantations in proximity to agricultural fields but also suggest potential inter-land spread of fungi, emphasizing the need for integrated management strategies across agricultural and forestry domains.