Initial Analysis of Plant Soil for Preliminary Characterization of the Possible Etiology of Disease of Seedling from <em>Ocotea monteverdensis</em>

Seedlings of the ecologically important and “critically endangered” tree, Ocotea monteverdensisis, are experiencing high mortality in the cloud forests of Monteverde, Costa Rica at the onset of the wet season, yet no previous work has been conducted to determine the disease etiology. Here, healthy and diseased Plant Root and adjacent Bulk soils were analyzed for total organic carbon and nitrogen (N), respiration, nitrate, and ammonium, and DNA sequence-based bacterial and fungal community composition. All N metric levels were greater in Diseased vs. Healthy Plant Root soils, which could enhance pathogen growth and pathogenic mechanisms. Greater DNA percentages from several potential pathogens were found in Diseased vs. Healthy Plant Root soils, suggesting a root pathogen etiology. The DNA percentage of the fungus Mycosphaerella was present at greater levels in the Diseased Plant Root soils than other potential pathogens (about 11.7% vs. &lt; 3.2%). Mycosphaerella causes similar diseases in other plants, including coffee, often after onset of the wet season. Similarly, the O. monteverdensis disease occurs in seedlings planted within or near former coffee plantations often at wet season onset. Although fungal pure culture isolation and transmission studies are needed, this is the first evidence of a potential etiologic agent of this disease.