Progress towards Sustainable Control of Xylella fastidiosa subsp. pauca in Olive Groves of Salento (Apulia, Italy)

Abstract

Xylella fastidiosa subsp. pauca is the causal agent of “olive quick decline syndrome” in Salento (Apulia, Italy). On April 2015, we started interdisciplinary studies to provide a sustainable control strategy for this pathogen that threatens the multi-millennial olive agroecosystem of Salento. Confocal laser scanning microscopy and fluorescence quantification showed that a zinc-copper-citric acid biocomplex—Dentamet®—reached the olive xylem tissue either after the spraying of the canopy or injection into the trunk, demonstrating its effective systemicity. The biocomplex showed in vitro bactericidal activity towards all X. fastidiosa subspecies. A mid-term evaluation of the control strategy performed in some olive groves of Salento indicated that this biocomplex significantly reduced both the symptoms and X. f. subsp. pauca cell concentration within the leaves of the local cultivars Ogliarola salentina and Cellina di Nardò. The treated trees started again to yield. A 1H-NMR metabolomic approach revealed, upon the treatments, a consistent increase in malic acid and γ-aminobutyrate for Ogliarola salentina and Cellina di Nardò trees, respectively. A novel endotherapy technique allowed injection of Dentamet® at low pressure directly into the vascular system of the tree and is currently under study for the promotion of resprouting in severely attacked trees. There are currently more than 700 ha of olive groves in Salento where this strategy is being applied to control X. f. subsp. pauca. These results collectively demonstrate an efficient, simple, low-cost, and environmentally sustainable strategy to control this pathogen in Salento.

Agro-active endo-therapy treated Xylella fastidiosa subsp. pauca-infected olive trees assessed by the first 1H-NMR-based metabolomic study

“…pauca cell concentration in olive trees 7 . Treated plants continue to vegetate and keep their productivity 8 , 9 . In addition to assessing disease control by quantitative PCR analyses, upon the foliar treatments with the biocomplex, OQDS biomarkers and metabolic pathways re-programming have been investigated by 1 H NMR-based metabolomics 8 .…”

“…Treated plants continue to vegetate and keep their productivity 8 , 9 . In addition to assessing disease control by quantitative PCR analyses, upon the foliar treatments with the biocomplex, OQDS biomarkers and metabolic pathways re-programming have been investigated by 1 H NMR-based metabolomics 8 . This methodology, based on spectroscopic analyses of xylematic extracts obtained from leaves, enabled the identification of specific disease-related metabolites.…”

Trunk Injection as a Tool to Deliver Plant Protection Materials—An Overview of Basic Principles and Practical Considerations

“…'Tree Tech ® OTC' is an oxytetracycline calcium complex registered for use in crop-bearing peaches and pears for bacterial blast, blossom blight, and fire blight management, and X-disease of peaches; however, there are few other bactericides registered for injection in crop-bearing trees. Oxytetracycline Effective [136,161] Most recently, injection experiments have extended beyond fungicides, insecticides, and bactericides to include other compounds such as plant defense activators [114,161,174], RNA [28,175], plant growth regulators [176], nanoparticles [177][178][179], novel antimicrobial molecules [180], essential oils [181], biofertilizers [182], nutrients [183], nano-carrier treatments [97], and bacteria [157,[184][185][186]. However, none are currently used on a commercial basis.…”

Transmission and distribution of Xylella fastidiosa subsp. pauca in olive trees as a parameter for managing olive quick decline syndrome

“…The management of diseases in crops caused by the systemic bacterium X. fastidiosa is a challenge based on the complexity of interactions between bacterium and hosts (vectors and plants) and the environment (Sicard et al, 2018). Although published experiments have shown some positive effects of delivered molecules reducing symptom development and bacterial multiplication (Muranaka et al, 2013;Navarrete & De La Fuente, 2014;Scortichini et al, 2021), there is currently no control measure available to eliminate the bacteria from a diseased plant in open field conditions (Bragard et al, 2019;Kyrkou et al, 2018;Morelli et al, 2021). On the other hand, one example of successful management of disease caused by X. fastidiosa is for CVC (Coletta-Filho et al, 2020), where the main actions for control included the exclusion of the pathogen from propagative vegetative material, inoculum reduction in the field by uprooting diseased plants and/or pruning of branches with symptoms, plus the systematic control of vectors (Bassanezi et al, 2021;Gravena, 1998).…”