at Bonanza Creek and other sites. Leaves were Diseases in Alaska specifically tested for phytoplasma and several viruses using PCR (polymerase chain reaction) technique. Nancy Robertson, Research Plant Pathologist, USDA Preliminary results were positive for ilarviruses (a Agricultural Research Service; Lori Winton, Pathologist, specific viral genus) and negative for phytoplasmas. Forest Health Protection Further molecular analysis (genetic sequencing) and characterization are ongoing for definitive viral Aerial survey and site visit reports in Southcentral taxonomic identification. Once identified, ecological and Interior Alaska have noted birch branch dieback, and epidemiological studies of the virus(es) would drought stress damage, and a general decline in tree help to ascertain their importance to the overall health condition since at least 2005. Like other tree declines, condition of birch trees and birch decline in Alaska. there is no obvious single cause for the gradual death of birch trees in Alaska, and it may be caused by a Historically, there has been limited research combination of drought and diseases or insects. In concerning viruses of forest trees, and documentation northeastern North America, birch decline has been usually involved viruses that were commonly found attributed to environmental changes. Recently, birch in horticultural trees and shrubs. Viruses of birch in decline has been observed in several birch forests in the USA include only the following three fruit tree Canada and the northern United States. While the viruses: Prune dwarf virus (PDV), Prunus necrotic symptoms of decline may be subtle initially, the most ringspot virus (PNRSV), and Apple mosaic virus obvious and damaging birch diseases in Alaska are (ApMV). Three additional viruses, Tobacco necrosis caused by fungi that produce highly visible conks or virus (TNV), Tobacco rattle virus (TRV), and Cherry mushrooms. The most common fungal pathogens leaf roll virus (CLRV), have been documented on of birch are: birch conk (Piptoporus betulina), birch trees from the United Kingdom. Interestingly, false tinder conk ( igniarius), cinder conk none of these viruses are transmitted by insects/mites (Inonotus obliquus), tinder conk (), - the first group of viruses (PDV, PNRSV, ApMV) and yellow cap mushroom (Pholiota spp.). is strictly transmitted by pollen or seed, TNV by a , and TRV and CLRV by specific nematodes. In 2012, unhealthy birch trees were observed in In Alaska, ApMV has been confirmed in susceptible Southcentral and Interior Alaska, with abnormalities apple tree cultivars and TRV has been detected in of varying types and severities. The most noticeable two ornamental perennials, peonies (Paeonia sp.) and and striking symptoms were numerous large brooms bleeding-heart (Dicentra sp.). Studies regarding the (concentrated, prolific branching) growing off the presence of the other four viruses in Alaska have not main stems of birch trees (Figures 30 and 31) in the been conducted. Work on the species identities and Bonanza Creek Experimental Forest and along the roles of viruses on birch in Alaska will continue, with Parks Highway in Denali State Park. The leaves on more results anticipated in the coming year.  brooms were relatively small, and displayed virus-like symptoms that included line and oak-leaf patterns, ringspots, and mottling (Figure 32). In general, broom symptoms are attributed to infection by specific parasitic plants or viral, phytoplasmal, or fungal pathogens. Several fungal species in the genus Taphrina are known to cause broom symptoms on birch trees, but have not been officially confirmed in Alaska.

Assays were implemented for detection and confirmation of viruses and phytoplasmas. Collections were made from trees with broom and/or leaf mottle/mosaic symptoms Figure 30. A birch broom at Porcupine Campground on the Kenai Peninsula. 32 U.S. Forest Service Alaska Region, State & Private Forestry DISEASES: ESSAY

Figure 31. Birch brooms at Bonanza Creek Experimental Forest.

Figure 32. Virus-like symptoms on birch leaves collected from a broom.

Forest Health Conditions in Alaska - 2012 33