SNC Disease Cycle

Infection of needles takes place in late-spring and early-summer, when ascospores are discharged from mature fruiting bodies (pseudothecia) on infected needles. Spore release coincides with the emergence and elongation of new foliage from buds, and newly formed needles are highly susceptible to infection (little or no infection of older needles occurs). Ascospores are wind and water-splash dispersed, and cause infection when they land on susceptible foliage, germinate, and enter needles through needle stomates. The threadlike body of the fungus (hyphae) continues to grow in the intercellular (between cells) space within the needle over many months, and fruiting bodies begin to develop in stomatal cavities (the epistomatal chamber). Under “ideal” conditions, immature pseudothecia may be visible on needles within 6 months of infection. Infection by one spore may result in the development of many pseudothecia on a single needle, because the fungus is able to expand within leaves in the months and years following infection. The lifecycle is completed when pseudothecia mature, and release ascospores in the spring. Because infection can increase on infected needles over several years, relatively more fungal biomass and fruiting bodies are present within/on older needles compared to younger needles. As a higher proportion of stomates on a needle become blocked by the fungal fruiting bodies, there is increase likelihood that the needle will be shed.