A recent study sheds light on the significant effects of Candidatus Liberibacter asiaticus (CLas), the bacterium responsible for citrus greening disease, on the root systems of grafted 'Valencia' orange trees. The findings reveal that root system reductions caused by the infection are more extensive than the corresponding aboveground declines, underscoring the hidden yet critical impact of the disease below the soil surface.
Huanglongbing (HLB), or citrus greening, is associated with a phloem-limited bacterial pathogen that causes extensive systemic damage to citrus trees that results in low yields, poor fruit quality, and whole tree decline. In Florida, the disease is associated with the putative pathogen Candidatus Liberibacter asiaticus (CLas) and transmitted by the Asian citrus psyllid (Diaphorini citri). Currently, HLB is the most significant threat to the global citrus industry and has already drastically reduced production in Florida, where it is now considered endemic. Although research of HLB has been extensive since the pathogen was first detected in the Americas, the understanding of the movement and distribution of CLas after infection is limited.
Researchers examined the physiological and structural changes in infected trees, emphasizing the challenges of managing citrus greening. While the visible effects of the disease on tree canopies and fruit production are well-documented, this study highlights the disproportionate vulnerability of root systems to the infection. The results suggest that the disease undermines the tree's foundational support and nutrient uptake mechanisms more significantly than previously understood.
This study further highlights the challenges of studying Candidatus Liberibacter asiaticus (CLas) infection in Florida due to the endemic nature of Huanglongbing (HLB). Using infected and noninfected field-grown trees, researchers found that while bacterial loads were higher in leaves, root systems suffered disproportionately greater growth reductions, with fibrous roots experiencing the most loss. This confirms that fibrous root loss is an early consequence of CLas infection, contributing significantly to tree decline. However, the connections between root loss, bacterial colonization, phloem damage, and carbohydrate metabolism remain unclear. The study underscores the importance of protecting young citrus trees from psyllids through insecticides or infection-prevention techniques to ensure healthy growth during early field establishment.
These insights hold vital implications for citrus growers and agricultural scientists. Understanding the belowground impact of CLas infections could guide more effective interventions, improve management strategies, and inform the development of rootstock selections better suited to resist the disease's effects.
According to the author: "We conducted this research as part of our ongoing efforts to help citrus growers manage huanglongbing (HLB, citrus greening) a bacterial disease that has devastated the Florida citrus industry and is affecting citrus production areas around the world. HLB has been known for some time to lead to fibrous root decline, but the extent of the damage occurring belowground had not yet been clearly documented. By using individual protective covers (IPCs) and conducting whole tree excavations, we documented for the first time the damage HLB has been inflicting on the different parts of the root system in relation to the damage occurring aboveground. The study also documents the efficacy of IPCs in preventing HLB in young citrus trees. The findings will be important for citrus growers and other citrus researchers trying to manage HLB."
This study was led and conducted by PhD candidate Caroline Tardivo as part of her
PhD research, her advisor and associate professor Dr. Ute Albrecht, and contributing
authors associate professor Dr. Fernando Alferez, PhD candidate Larissa Nunes, and
former PhD student Dr. Leigh Archer.
Dr. Albrecht is Associate Professor of Plant Physiology, University of Florida Southwest Florida Research and Education Center.
The full article can be found on the ASHS HortScience electronic journal website at: https://doi.org/10.21273/HORTSCI17669-23
Established in 1903, the American Society for Horticultural Science is recognized around the world as one of the most respected and influential professional societies for horticultural scientists. ASHS is committed to promoting and encouraging national and international interest in scientific research and education in all branches of horticulture.
Comprised of thousands of members worldwide, ASHS represents a broad cross-section of the horticultural community-scientists, educators, students, landscape and turf managers, government, extension agents and industry professionals. ASHS members focus on practices and problems in horticulture: breeding, propagation, production and management, harvesting, handling and storage, processing, marketing and use of horticultural plants and products. To learn more, visit ashs.org.
