Introduction
In Salento (Apulia, South Italy), Xylella fastidiosa subsp. pauca (Xf) has caused significant damage to the local economy, highlighting the urgent need for crop renewal aimed at developing new production chains and increasing the biodiversity of the area. To achieve this, it is essential to use species that are considered immune or resistant to the bacterium. The almond tree (Prunus dulcis Mill.) is an excellent candidate, as some varieties have shown resistance to the bacterium and can also grow in conditions of water shortage. Additionally, almond tree cultivation holds significant traditional and economic value in the Apulia region.
Goals
In this work, we report the performance of two almond cultivars, “Filippo Ceo” and “Tuono”, which are presumed to be resistant to Xf. We evaluated changes in various physiological parameters, focusing on the proline content and the expression profiles of genes associated with its metabolism, as proline plays a key role in plant stress responses. Insights from this analysis may reveal stress tolerance mechanisms and support sustainable strategies to combat Xf.
Methodology
his study was conducted in an 18-year-old almond orchard in Veglie (Lecce, Italy), an area that has been affected by Xf since 2015, using a randomized block design with seasonal sampling. The bacterial concentration was measured in CFU/ml (D’Attoma et al. 2019), while the proline concentration was determined using the method developed by Bates et al. (1973). Our gene expression analysis involved RNA extraction with a CTAB-based protocol, cDNA synthesis with TaqMan® reagents, and Real-Time PCR using SYBR Green. Expression levels were calculated using the log2 2−ΔΔCt method.
Results
During the 2023–2024 trial, no trees exhibited significant symptoms of Xf infection. The PCR analyses identified approximately one-third of Xf-positive plants, which showed bacterial concentrations below 10 3 CFU mL −1 . The free proline content was low in healthy uninfected plants but significantly increased in Xf-positive ones of both cvs, with no significant variation across different sampling periods. Moreover, genes linked to proline metabolism were induced by Xf, with notable differences in expression levels between the two cvs.
Conclusions
Proline is a multifunctional amino acid that plays a pivotal role in plant stress responses. In the context of resistance to Xf infection, proline accumulation and its metabolic pathways may provide insights into the mechanisms underlying stress tolerance and adaptation. Such findings may be useful in the development of targeted breeding programs and sustainable management strategies to mitigate the impact of Xf.
