Screening of Olive Biodiversity Defines Genotypes Potentially Resistant to Xylella fastidiosa.

Stefano Pavan,Alessio Aprile,Francesca Nicolì,Marzia Vergine,Luigi De Bellis,Andrea Luvisi,Cinzia Montemurro,Chiara Delvento,Michele Antonio Savoia,Carmine Negro,Valentina Fanelli,Vito Montilon,Erika Sabella,Leonardo Susca,Luigi Ricciardi,Franco Nigro,Concetta Lotti

doi:10.3389/fpls.2021.723879

Abstract

The recent outbreak of the Olive Quick Decline Syndrome (OQDS), caused by Xylella fastidiosa subsp. pauca (Xf), is dramatically altering ecosystem services in the peninsula of Salento (Apulia Region, southeastern Italy). Here we report the accomplishment of several exploratory missions in the Salento area, resulting in the identification of thirty paucisymptomatic or asymptomatic plants in olive orchards severely affected by the OQDS. The genetic profiles of such putatively resistant plants (PRPs), assessed by a selection of ten simple sequence repeat (SSR) markers, were compared with those of 141 Mediterranean cultivars. Most (23) PRPs formed a genetic cluster (K1) with 22 Italian cultivars, including ‘Leccino’ and ‘FS17’, previously reported as resistant to Xf. The remaining PRPs displayed relatedness with genetically differentiated germplasm, including a cluster of Tunisian cultivars. Markedly lower colonization levels were observed in PRPs of the cluster K1 with respect to control plants. Field evaluation of four cultivars related to PRPs allowed the definition of partial resistance in the genotypes ‘Frantoio’ and ‘Nocellara Messinese’. Some of the PRPs identified in this study might be exploited in cultivation, or as parental clones of breeding programs. In addition, our results indicate the possibility to characterize resistance to Xf in cultivars genetically related to PRPs.

Highlights

Xylella fastidiosa (Xf ) is a Gram-negative bacterium affecting more than 350 plant species, including tree crops of major economic importance (Zarco-Tejada et al, 2018)
Exploratory missions were carried out in the Province of Lecce (Salento) for a periodical screening of 49 plants reported by local farmers to stand out in orchards heavily infected by Xf (Figure 1)
The distribution of S and C values associated with putatively resistant plants (PRPs) and control plants (CPs) are reported in Supplementary Figure 1

Summary

Introduction

Xylella fastidiosa (Xf ) is a Gram-negative bacterium affecting more than 350 plant species, including tree crops of major economic importance (Zarco-Tejada et al, 2018). Disease symptoms include leaf scorching, leaf and twig wilting and, in a second phase, tree die-back, due to the formation of bacterial biofilms in xylematic vessels (Purcell and Hopkins, 1996). According to spatially explicit economic models, Xylella fastidiosa Resistance in Olive. Xf may impact Italian olive growers from 1.5 to 5.9 billion euros in the 50 years and cause further economic losses by affecting cultural heritage and landscape values (Schneider et al, 2020). It was shown that resistance in ‘Leccino’ and ‘FS17’ is associated with reduced levels of bacterial growth in xylematic vessels (Saponari et al, 2016; Giampetruzzi et al, 2020)

Methods

Results

Conclusion