Reducing tree decline of Casuarina equisetifolia in Guam through replacement of bacterial wilt infected trees and research into the bacterial microbiomes of trees and associated termites

Project Overview

Project Type: Research and Education
Funds awarded in 2019: $304,273.00
Projected End Date: 12/31/2022
Host Institution Award ID: G259-19-W7500
Grant Recipients: University of Guam; University of Hawaii; Louisiana State University
Region: Western
State: Guam
Principal Investigator:
Dr. Robert Schlub
University of Guam

Information Products


  • Additional Plants: trees


  • Crop Production: agroforestry

    Proposal abstract:

    Ironwood (Casuarina equisetifolia), recognized as an important tree species by the Natural Resources Conservation Service (NRCS) are under attack. Ironwood is one of the dominant, naturally occurring and propagated agroforestry species in the Pacific due to its ability to withstand salt spray, typhoon strength winds, and poor soil conditions. The importance of ironwood is underscored by the fact that it has been on Guam for thousands of years and is tightly integrated into the island’s environment and its many ecosystems.  Guam’s NRCS Environmental Quality Incentives Program rewards applications for planting ironwood as a riparian forest buffer or windbreak, and as a source of ironwood needle organic mulch. In a 2002 forestry inventory, it was reported that Guam’s tree population was healthy and numbered 116,000. In a survey funded by WSARE in 2008, it was estimated that 51% of the trees were showing signs of a progressive dieback now referred to as ironwood tree decline (IWTD). The Guam Department of Agriculture ceased its yearly 25,000 seedling give-away program in large part due to IWTD. The seedling program provided trees to farmers, the public, and government agencies for windbreaks, riparian buffers, erosion control, land reclamation, and island beautification. In Guam’s 2010-2015 Statewide Forest Resource Assessment and Resource Strategy report it was stated that ironwood decline was impacting the health of Guam’s forests and that determining its cause and finding solutions should be a priority for the future. Bacterial wilt will be reduced as a result of tree plantings, increasing genetic diversity of tree population, advancing scientific discovery, and education of the public and scientific community. Seven hundred trees of four off-island cultivars will be out planted in 25 agroforestry projects on producer’s farms and given to the public and government agencies. Various biological components of Ralstonia solanacearum and wetwood bacteria will be examined to determine the origin of these bacteria. Since termites are significantly associated with IWTD, we will investigate whether they carry ironwood bacteria in their guts as a first step to elucidate their potential role as vectors. Over the course of the project, two ½ day workshops will be offered to the public, farmers and foresters, where they will receive instructions on tree care practices such as disinfecting pruning tools to reduce the spread of bacteria. They will also learn that the common termite species found in ironwood trees is Nasutitermes, which is not a threat to homes. Researchers will be brought to Guam for a 4-day workshop, and roundtable discussion about bacterial wilt and bacterial wetwood, and implications for Guam and the Pacific Islands if R. solanacearum were to move from ironwood into other tree species. Currently Guam is the only US location were R. solanacearum occurs in trees whereas in China bacterial wilt disease occurs in Casuarina, Olea, Morus, and Eucalyptus. Some rank bacterial wilt disease as the most important disease in China due to its wide distribution and cumulative losses on trees, ornamentals, medicinal plants and many crops.

    Project objectives from proposal:

    Obj 1 Yr 1-2:UOG: Restoring ironwood as an agroforestry species in Guam by planting new agroforestry projects, restoring projects decimated by bacterial wilt, and establishing conditions for natural incorporation of new genes into Guam’s ironwood tree population.

       Obj. 1 Sub-obj. 1: UOG: Test trees for bacterial wilt in 10 deteriorating agroforestry projects, those that test positive flag for replacement with
        150 trees of mixed cultivars.

       Obj. 1 Sub-obj. 2: UOG:  Construct 15 new ironwood agroforestry projects using 150 trees consisting of a mixture of tree cultivars.

    Obj. 2 Yr 1-2: UH: Restoring ironwood as an agroforestry species in Guam through research into the bacterial wilt pathogen to determine the origin of Guam’s infection and its genomic biology.

    Obj. 3 Yr 1-2-3: UH and LSU: Restoring ironwood as an agroforestry species in Guam through research into the bacterial flora of ironwood trees and the guts of termites.

       Obj. 3 Sub-obj. 1: UH: Determine the role of vascular colonization of R. solanacearum and wetwood bacteria species Klebsiella sp. in IWTD.

       Obj.3 Sub-obj. 2:UH: Determine bacterial flora of ironwood trees and their likely role in IWTD.

        Obj.3 Sub-obj. 3: LSU: Determine if termites carry ironwood bacteria and thus, might be responsible for their movement.

    Obj. 4 Yr 2-3:UOG: Restoring ironwood as an agroforestry species in Guam through awareness and action of the local and scientific communities.

       Obj. 4 Sub 1:UOG: Through two ½ day workshops, attendees will learn about the care of the ironwood trees and its uses in agroforestry. A total of   
        400 trees will be given away.

       Obj. 4 Sub 2: UOG/UH/LSU: PI and Extension/outreach representative in the third year will conduct a four-day workshop/conference on
       bacterial wilt and other components of IWTD. Proceedings of the meeting will be added as an appendix to the Guam Ironwood Tree guide.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.