DEVELOPMENT OF DWARF MISTLETOE INFECTIONS ON INOCULATED WESTERN HEMLOCK TREES IN SOUTHEAST ALASKA

In the autumn of 1977, 1978, and 1979, mature seeds of hemlock dwarf mistletoe (Arceuthobium tsugense) were placed on needles and twigs of young western hemlock trees growing on a clearcut in Juneau, Alaska to provide information on seed retention and germination, infection development and survival, and generation time. Retention over one winter of 1,956 placed seeds averaged 65 percent while germination of retained seeds was 33 percent. Two hundred and sixty infections developed, 78 percent of which produced dwarf mistletoe shoots; however, over the 11 to 12 years that infections were observed, no seeds were produced and shoots were frequently broken or damaged. Plant damage, branch death, pollination biology, and environmental conditions are discussed as possible reasons for the lack of seed production and failure to complete the life cycle. Comparisons are made to other inoculation studies with A. tsugense. These comparisons indicate that the initial process of infection development, after mistletoe seeds are captured on needles or twigs, does not appear to account for the markedly lower infection levels that have been noted between stands in southeast Alaska and those further south.