Olive Cultivars Susceptible or Tolerant to Xylella fastidiosa Subsp. pauca Exhibit Mid-Term Different Metabolomes upon Natural Infection or a Curative Treatment

Abstract

Xylella fastidiosa subsp. pauca, is a bacterial phytopathogen associated with the “olive quick decline syndrome” (OQDS) causing severe economic losses to olive groves in Salento area (Apulia, Italy). In a previous work, we analyzed by 1H-NMR the metabolic pattern of naturally infected Ogliarola salentina and Cellina di Nardò susceptible cultivars untreated and treated with a zinc-copper citric acid biocomplex and we observed the treatment related variation of the disease biomarker quinic acid. In this study, we focused also on the Leccino cultivar, known to exhibit tolerance to the disease progression. The 1H-NMR-based metabolomic approach was applied with the aim to characterize the overall metabolism of tolerant Leccino in comparison with the susceptible cultivars Ogliarola salentina and Cellina di Nardò under periodic mid-term treatment. In particular, we studied the leaf extract molecular patterns of naturally infected trees untreated and treated with the biocomplex. The metabolic Leccino profiles were analyzed for the first time and compared with those exhibited by the susceptible Cellina di Nardò and Ogliarola salentina cultivars. The study highlighted a specificity in the metabolic response of the tolerant Leccino compared to susceptible cultivars. These differences provide useful information to describe the defensive mechanisms underlying the change of metabolites as a response to the infection, and the occurrence of different levels of disease, season and treatment effects for olive cultivars.

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

“…For the untreated samples, a higher relative content of phenolic compounds such as tyrosol and hydroxytyrosol moieties of oleuropein and its aldehydic forms and quinic acid were observed in the second sampling for all the analyzed cultivars, consistent with previous findings [39,50]. The analyses of the specific influence of the sampling period on metabolic profiles for infected cultivars indicated a specific rank (i.e., Leccino > Cellina di Nardò > Ogliarola salentina) for the observed discrimination between the two sampling periods [46]. Reproduced from [40].…”

“…The metabolic profiles evaluation focused in a specific time span (six months treatment April to September after six months suspension), with the aim to evaluate any possible memory effects due to previous treatments persisting after suspension periods. Therefore, metabolomic analyses were performed on leaf sample extracts from infected and untreated trees in two specific samplings (March, before the start and October after the end of treatments) over the last treatment year [46].…”

“…pauca, treated with Dentamet ® or healthy. Based on [39,40,46]. Note quinic acid as a biomarker for naturally infected trees, and mannitol for treated and healthy Leccino trees.…”

“…The tree crown nebulization of Dentamet ® (a biocomplex containing zinc, copper, and citric acid) during spring, summer, and early autumn significantly reduced both the symptoms (i.e., twig and branch wilting) and the bacterial cell density within the leaves of the sensitive olive cultivars Ogliarola salentina and Cellina di Nardò as measured by quantitative real-time PCR [33,34]. Dentamet ® treatments resulted in a rapid reprogramming of some indicative metabolic pathways, as observed by metabolomics, which re-established a more normal tree physiology [39,40,46]. The yearly amount of copper released in the environment by means of this control strategy satisfies the current requirements aimed at avoiding the accumulation of copper in the soil [73].…”

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

“…In Italy, the central-southern territory is largely dedicated to olive cultivation. Apulia (South-East Italy) is the region with the largest production and olive oil is among the most important sources of income for the local economy 2 . In addition, century-old olive trees represent a unique landscape part of the cultural heritage of the region with high touristic value.…”