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Ex situ conservation of American chestnut (Castanea dentata (Marsh.) Borkh.) and butternut (Juglans cinerea L.), a review by Ken McIlwrickl, S. Wetze12, T. ~e a r d m o r e~ and K. ~o r b e s~ Two tree species native to North America, American chestnut (Castanea dentata (Marsh.) Borkh.) and butternut (Juglans cinerea L.), which have experienced rapid declines in their populations due to similar stressors (disease and changes in land use), are used as examples of how these species would benefit from ex situ conservation efforts. Current and past ex situ and in situ conservation efforts for these species are discussed and the focus of this review is on two key research areas: 1) what needs to be preserved (genetic information) and 2) how to preserve these trees or germplasm.Key words: butternut, American chestnut, Cryphonectria parasitica, Sirococcus clavigignenti-juglandacearum, ex situ conservation Deux espkces arborescentes indigknes de 1'Amtrique du Nord, le chstaignier amtricain (Castanea dentata (Marsh) Borkh.) et le noyer cendrt (Juglans cinerea L.), qui ont connu une diminution rapide de leur population suite A des stress similaires (la maladie et les changements dans l'utilisation du territoire), sont utilistes pour illustrer comment des espkces pourraient bCnCficier des efforts de conservation ex situ. Les efforts actuels et antkrieurs de conservation ex situ et in situ dans le cas de ces espkces sont discutts et le point central de cette revue porte sur deux domaines de recherche courante: 1) ce qu'il faut prtserver (information gCnCtique) et 2) comment prtserver ces arbres ou leurs germoplastes.

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Butternut (Juglans cinerea L.), an early successional riparian hardwood species native to Canada and the United States, is under serious threat from a nonnative fungal pathogen, Ophiognomonia clavigignenti-juglandacearum. Since it was first reported in Canada in 1990, this fungal pathogen has spread rapidly and established in New Brunswick in 1997. Apart from the first report in 1997 and another in 2004, no surveys have been conducted to assess the spread of the pathogen in the province. The purpose of this research was to survey butternut throughout its range in New Brunswick, evaluate disease occurrence as well as tree health, and investigate the impact of different topographic and tree health factors on canker incidence. Results showed that the disease has spread throughout the range of butternut in New Brunswick. The disease likely only recently (2007) spread to the northeastern-most populations, given that lower rates of canker occurrence and higher health ratings are found further away from the point of initial occurrence of the disease. Although canker incidence is high throughout the province, tree dieback is minimal, and trees still producing nuts could support opportunities for ex situ conservation. Because of the rate of pathogen spread in the province, implementing a tree improvement strategy might be the only means for maintaining the butternut genome on the landscape.