Internal hyphae in young, symptomless needles of Picea abies: electron microscopic and cultural investigation

Abstract

Results from cultural investigations were correlated with scanning electron microscope observations and give an introduction to the interaction of endophytic hyphae of Lophodermium piceae (Fckl.) Höhn. and other fungi with living tissues of green, symptomless needles of Norway spruce (Picea abies Karst.). The frequency of endophytic needle fungi was determined by the culture of surface-sterilized needles harvested from two trees. Lophodermium piceae was found to be the most important colonizer of symptomless needles; the infection rates ranged from about 3 to 7%. The presence of fungal hyphae in living needle tissues of symptomless, current year and older Norway spruce needles was demonstrated by scanning electron microscopy. The observed mycelia were both intercellular and intracellular. The hyphal diameters varied significantly and striking swellings of unknown function were observed along internal hyphae. The observed needle colonization is discussed in connection with the spreading of fungal endophytes in the host tissues during the endophytic phase of L. piceae in Norway spruce needles.