A recent study sheds light on the significant effects of Candidatus Liberibacter asiaticus (CLas), the bacterium responsible for HLB, 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. That finding underscores the hidden yet critical impact of the disease below the soil surface.
Researchers with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) examined the physiological and structural changes in infected trees, emphasizing the challenges of managing HLB. 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 was previously understood.
The study further highlights the challenges of studying CLas infection in Florida due to the endemic nature of 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.
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 HLB’s effects.
The study’s authors stated that they 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. They added that the study also documents the efficacy of individual protective covers in preventing HLB in young citrus trees.
Ph.D. candidate Caroline Tardivo and her advisor Ute Albrecht led and conducted this study. Contributing authors are Associate Professor Fernando Alferez, Ph.D. candidate Larissa Nunes and former Ph.D. student Leigh Archer. Albrecht is associate professor of plant physiology at the UF/IFAS Southwest Florida Research and Education Center.
See the full article here.
Source: American Society for Horticultural Science
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