Citizen Science Uncovers Phytophthora ramorum as a Threat to Several Rare or Endangered California Manzanita Species

Abstract

<jats:p> The Sudden Oak Death or SOD Blitzes consist of yearly surveys led by citizen scientists designed to map the distribution of Phytopthora ramorum, causing the forest disease called SOD, across Northern California. During the 2017 Santa Cruz County SOD Blitz, six rare or endangered Arctostaphylos (manzanita) species were found to be possibly symptomatic for the first time. Symptoms included branch cankers and associated canopy mortality, and affected multiple individuals per species. Isolates of Phytophthora ramorum were obtained from each of the six species and through a 30-day long inoculation experiment on live plants, Koch’s postulates were completed for each one of them, conclusively determining that they all are hosts of this pathogen. Two additional manzanita species were later found to be apparently symptomatic in Marin County. Inoculations on detached branches using an isolate of P. ramorum obtained from one of the six rare species from Santa Cruz County were successful, suggesting these two species may also be hosts of P. ramorum. Detached leaves of all eight species were also successfully inoculated at U.C. Berkeley in the Fall of 2018 and then again in the Spring of 2019. In these cases, the same isolate was used for all inoculations, in order to obtain information on the comparative susceptibility of the eight species in question. Both branch and leaf inoculations identified significant interspecific differences in susceptibility. The production of sporangia was low on all species, but it was not zero, suggesting that sporulation may cause within-plant and limited across-plant contagion, especially in rainy years. </jats:p>

Citizen science can add value to Phytophthora monitoring: five case studies from western North America

“…Given the very large number of samples collected and tested, it is no surprise that the SOD blitzes identified innumerable new outbreaks, although only one was in a county where P. ramorum had yet to be identified, resulting in a change in State and Federal policies (Garbelotto et al, 2021a). Likewise, several Arctostaphylos species were added to the list of federally regulated plant species thanks to the SOD blitzes (Garbelotto et al, 2020). The 2020 SOD blitzes identified the EU1 lineage, previously unreported in California forests, in a forest in Del Norte County (Garbelotto et al, 2021a).…”

Citizen Science and Monitoring Forest Pests: a Beneficial Alliance?

“…Citizen science can also be a cost-effective way of gathering specimens from across a wide geographic range, with further biological analysis undertaken by professionals. In this way, new hosts for Phytophthera ramorum were identified from samples obtained during the Sudden Oak Death Blitz in California [ 82 ].…”

“…Furthermore, citizen scientists can crowd-source the collection of physical samples for laboratory analysis, e.g. inoculation studies [ 82 ] or DNA analysis. Professionals can optimise sampling design, and in collaboration with citizen scientists (in terms of co-design), pest monitoring by citizen scientists can provide high-quality data.…”