CAP: Combining cultural and genetic approaches for grove success to unravel and enhance resistance/tolerance to Huanglongbing
Research by Caroline Roper, Ph.D., Philippe Rolshausen, Ph.D., Danelle Seymour, Ph.D., Jason Stajich, Ph.D., Ashraf El-kereamy, Ph.D., Ute Albrecht, Ph.D., Sarah Strauss, Ph.D., Ramdas Kanissery, Ph.D., Dario Cantu, Ph.D. and Jonathan Kaplan, Ph.D.
Article written by: Caroline Roper, Ph.D.
Article edited by: Ed Stover, Lukasz Stelinski, Peggy G. Lemaux
What is the research objective?
HLB is a major threat to US citrus production. It is highly destructive and lethal to commercial citrus cultivars making it the most serious current citrus disease. In the US, Candidatus Liberibacter asiaticus (CLas), is the primary bacterial species associated with HLB and the primary vector is the Asian Citrus Psyllid (ACP), Diaphorina citri. Despite years of research, there is no cure for HLB, and management practices focus on vector management/exclusion and maintaining tree health through nutrition regimes. Root collapse is an issue in HLB-impacted trees and a 2014 study suggested that CLas colonization leads to fibrous root decline prior to manifestation of above ground symptoms. The research objective of the proposed work is to investigate the root collapse associated with HLB-impacted trees and ways to mitigate it by promoting root health.
What is being done?
This work builds on our previous work that demonstrated that, as HLB severity increases, the microbes associated with the root (microbiome) becomes enriched in soil-borne pathogens (Figure 1). We are conducting experiments to empirically determine if these pathogens exacerbate the HLB-associated root (and canopy) decline. We have integrated field studies that test HLB resistant/tolerant rootstocks and use of soil amendments that promote root health to determine if they suppress pathogenic shifts in the microbiome and prolong tree longevity/productivity under HLB pressure. These field studies include newly planted and established groves to investigate the efficacy of soil ammendments and cover crops in both grove establishment and rehabilitation. To support our field trials and decipher potential mechanisms underlying the interaction of root health, the soil/plant microbiome and soil ammendments we are also conducting microbial community analyses on above and below ground compartments of trees in our field trials. We are integrating this research with a robust extension and outreach program in combination with an economic cost-benefit analysis structured around adoption of treatments that enhance root health into commercial citriculture.
Who is working on this project?
We have a broad team of academic faculty, scientists, postdoctoral scholars, graduate and undergraduate students working together to perform the work that underpins this project. Our techniques include in-field disease assessments and plant/soil sample collection in both California and Florida citrus groves. We are assessing root health below ground using a variety of metrics and specialized equipment, such as the rhizotron, which allows real time observation of root growth. At the microbial level, we are identifying and enumerating citrus root microbial communities by using metagenomics, which allows us to explain how microbial interactions are impacted by HLB. This work will inform us not only of the microbial populations enriched under the particular cultural practices we are testing, but also predict their particular function as possible therapeutics for treating HLB.
Funding source: Unites States Department of Agriculture, National Institute of Food and Agriculture, Specialty Crop Research Initiative, Emergency Citrus Disease Research and Extension (#2020-70029-33202).
