Conducting Forest Health research abroad

Araucaria humboldtensis is a threatened conifer endemic to New Caledonia, which is a Pacific island known for its unique and highly endemic flora. New Caledonia is considered one of the smallest biodiversity hotspots in the world. Araucaria humboldtensis populations are found growing in Southern New Caledonia and grow at altitudes of ca. 8oo to 1600 min high altitude shrubland, on ultramafic substrate. Over the last several decades, there have been observations of a general decline in populations of A. humboldtensis, which is manifested by massive resin exudation, branch and twig dieback, and eventual mortality. The observed symptoms are typical of a fungal canker disease, but no pathogen has been identified as a primary causal agent. The major objectives of this work are to i) identify primary causal agents of the decline symptoms, ii) elucidate the etiology of this potential disease, and iii) preserve unique genotypes of A. humboldtensis. From a preliminary survey from Mt. Humboldt in December 2014, Fusarium oxysporum, Fusarium solani and Chalara sp., which are known plant pathogens in other pathosystems, were isolated from bleeding cankers of several A. humboldtensis trees. Pathogenicity tests are needed to confirm if these isolated fungi are aggressive pathogens of A. humboldtensis. To understand the etiology of this decline, transects has been established among three populations of A. humboldtensis in Southern New Caledonia, where the health of the trees will be monitored over time. Symptomatic tissues have been sampled for associated fungi. Lastly, we plan to genotype and propagate A. humboldtensis individuals from all known populations. This work will support conservation efforts by identifying potential tolerant populations of A. humboldtensis.