Publication Date

Spring 2019

Degree Type


Degree Name

Master of Science (MS)


Environmental Studies


Rachel O'Malley


Avocado, Biodiversity, Colombia, Root Rot

Subject Areas

Agronomy; Agriculture; Environmental management


In recent years, small avocado producers in coastal Colombia returned to their farms after decades of war to discover they must battle the pathogen Phytophthora cinnamomi devastating their trees. While this disease is well-described in the U.S., Australia, and Europe, no previous research has examined environmental correlates of P. cinnamomi in avocado in the diverse tropical agroecosystem of the Colombian Montes de Maria. I used agroecosystem inventory, in-field diagnostics, and disease observations to describe avocado agroecosystem diversity and identify relationships among P. cinnamomi presence, root rot disease, slope, pH, soil compaction, elevation, and distance to the household in remote smallholder farms in the coastal mountains of Colombia. I also evaluated the accuracy of a locally accessible, low-cost bioassay for detecting the pathogen. Although P. cinnamomi proved to be ubiquitous in the region, soil compaction and increasing slope were both negatively related to disease incidence at the farm level, and some infected trees appeared healthy. Furthermore, the low-cost bioassay detected P. cinnamomi equally well as commercial immunostrips. As conflict reparations are negotiated in this remote region, small farmers should be compensated for retaining their highly diversified genetic stock, diverse cropping palettes, and indigenous techniques, as they may provide a refuge for avocado from the heavy disease burden in the steep and rocky growing terrain.