Biological Control of Pierce’s Disease of Grape by an Endophytic Bacterium

Abstract

Effective preventive measures and therapies are lacking for control of Pierce’s disease of grape caused by the xylem-colonizing bacterium Xylella fastidiosa responsible for serious losses in grape production. In this study we explored the potential for endophytic bacteria to alter the disease process. While most endophytic bacteria found within grape did not grow or multiply when inoculated into mature grape vines, Paraburkholderia phytofirmans strain PsJN achieved population sizes as large as 106 cells/g and moved 1 m or more within 4 weeks after inoculation into vines. While X. fastidiosa achieved large population sizes and moved extensively in grape when inoculated alone, few viable cells were recovered from plants in which it was co-inoculated with strain PsJN and the incidence of leaves exhibiting scorching symptoms typical of Pierce’s disease was consistently greatly reduced from that in control plants. Suppression of disease symptoms occurred not only when strain PsJN was co-inoculated with the pathogen by puncturing stems in the same site in plants, but also when inoculated at the same time but at different sites in the plant. Large population sizes of strain PsJN could be established in both leaf lamina and petioles by topical application of cell suspensions in 0.2% of an organo-silicon surfactant conferring low surface tension, and such treatments were as effective as direct puncture inoculations of this biocontrol strain in reducing disease severity. While inoculation of strain PsJN into plants by either method at the same time as or even 4 weeks after that of the pathogen resulted in large reductions in disease severity, much less disease control was conferred by inoculation of PsJN 4 weeks prior to that of the pathogen. The expression of grapevine PR1 and ETR1 within 3 weeks of inoculation was substantially higher in plants inoculated with both X. fastidiosa and strain PsJN compared with that in plants inoculated only with the pathogen or strain PsJN, suggesting that this biological control agent reduces disease by priming expression of innate disease resistance pathways in plants that otherwise would have exhibited minimal responses to the pathogen. Strain PsJN thus appears highly efficacious for the control of Pierce’s disease when used as an eradicant treatment that can be easily made even by spray application.

Secondary Metabolites in Xylella fastidiosa–Plant Interaction

“…In addition, maintaining healthy microbiota and the presence of cultivar-specific microbes may support the resilience of the resistant olive cultivar Leccino to Xf infection [ 38 ]. This evidence was also confirmed in other pathosystems where experimental evidence suggests that plant colonization by specific bacterial endophytes is marked by a change in the expression of key genes in central metabolic and by priming expression of innate disease resistance pathways in plants that result in the reduction of disease [ 39 , 40 ]. At the same time, endophytic fungi can influence the plant’s metabolism by increasing the content of antioxidant compounds in the host [ 41 ].…”

Induction of systemic resistance to Agrobacterium tumefaciens by endophytic bacteria in grapevine

“…Concerning the priming concept, increased phytoalexin accumulation in leaves and stems of A. tumefaciens‐ inoculated plantlets after root treatments with Sn48 and Sa14 suggests a pathogen‐dependent activation of defence responses. In line with this concept, Baccari et al (2019) reported priming expression of the innate disease resistance pathway mediated by Paraburkholderia phytofirmans PsJN in grapevine inoculated with Xylella fastidiosa . Our findings revealed that Sn48 colonized grapevine roots but not aboveground plant parts, and enhanced trans ‐resveratrol, trans ‐piceid, and δ‐viniferin accumulation in all plant tissues of plantlets inoculated by A. tumefaciens .…”

The Effect of Plant Genotype, Growth Stage, and Mycosphaerella graminicola Strains on the Efficiency and Durability of Wheat-Induced Resistance by Paenibacillus sp. Strain B2

“…PGPR-mediated ISR enhances the formation of physical barriers such as callose and lignin, the synthesis of plant defense chemicals as reactive oxygen species (ROS), phytoalexins and phenolic compounds (Benhamou, 1996; Samain et al, 2017), but certain PGPR do not induce PR proteins (Hoffland et al, 1995). On the other hand, the upregulation of genes, known as SAR pathway markers, such as PR2, chitinases and PR1 , have been observed with PGPR including the genera Bacillus, Pseudomonas, Paenibacillus , and Paraburkholderia (Park and Kloepper, 2007; Samain et al, 2017; Baccari et al, 2019). The overexpression of PR1 induced by PGPR might be explained by the abiotic stress as a response to root colonization by bacteria (Timmusk and Wagner, 1999).…”