Fungi associated with shoot dieback of Pinus mugo subsp. mugo in the Polish Tatra Mountains

Abstract

Dieback of dwarf pine scrub (Pinus mugo subsp. mugo) shoots can limit the growth of this species in subalpine areas of the Carpathian Mountains. In July 2023, extensive shoot decline was observed in P. mugo patches in the West Tatra Mountains in southern Poland. Symptomatic shoots showed shoot tip dieback and red-brown needle discoloration. Internal symptoms included dark discoloration of the pith parenchyma and necrotic lesions in shoot periderms. In this study, we described the symptoms of P. mugo shoot dieback and surveyed the culturable fungi from asymptomatic and symptomatic P. mugo shoots, as well as the bases of needles growing from shoots. In addition, we conducted phylogenetic analyses to distinguish between potential cryptic species of Sydowia polyspora. The dwarf pine scrub shoots and needles were sampled from four patches in the Polish Tatra Mountains. In total, 128 distinct taxa were identified. Ascomycota was dominant, representing 96.6% of the isolates. Among the taxa identified, Sydowia polyspora crypt. sp. I, Lachnellula calyciformis, Mollisia sp. 8, Tympanis sp., Epicoccum mezzettii, E. nigrum, Infundichalara sp., Lophium mytilinum, Cytospora sp., Soosiella sp., Cladosporium westerdijkiae and Hendersonia pinicola were most frequently isolated. In most cases, tissue type and sample site significantly affected the abundance and composition of colonizing fungi. Only S. polyspora was found consistently in all sample types, suggesting that this fungus may be responsible for the shoot dieback of P. mugo. Phylogenetic analyses demonstrated that S. polyspora should be treated as a species complex containing at least four cryptic species (referred to as groups I–IV), that are highly host-specific to different conifer species. We also found several other well-known pathogens, namely Allantophomopsis pseudotsugae, Botrytis cinerea, Cytospora sp., Fusarium sp., Sirococcus conigenus and Tympanis sp., which may cause considerable damage to Pinus spp. shoots. Among them, only Cytospora sp., and Tympanis sp. were found often. This is the first comprehensive survey of the fungi associated with extensive shoot dieback of P. mugo in the Carpathian Mountains, and this research led to the discovery of numerous new fungal species associated with P. mugo.