Phenotypic and genetic characterization of Pseudomonas syringae strains associated with the recent citrus bacterial blast and bacterial black pit epidemics in Tunisia

Abstract

In the spring of 2012, symptoms of a disease resembling citrus blast and citrus black pit were observed in some orchards in Tunisia. The epidemic spread rapidly in the following years. Twenty‐four commercial citrus orchards from four Tunisian regions showing characteristic symptoms of bacterial diseases were surveyed during a 3‐year study. Eighty‐eight Pseudomonas‐like bacterial isolates were successfully obtained from the northeast and west of Tunisia. No isolates were recovered from the central region. Overall, 46 isolates were identified as Pseudomonas syringae pv. syringae and most of them showed similar phenotypic and genetic profiles. The virulence of three selected isolates differed from one plant cultivar to another as well as from the type of plant organ used for the inoculation. In a bioassay test, all isolates produced syringomycin, which was confirmed by molecular detection based on the syrB and syrD genes. Only EC122 possessed syrD but not syrB. DNA fingerprints, based on repetitive sequence‐based polymerase chain reaction (rep‐PCR) and PCR melting profile (PCR MP), were used to determine the potential genetic diversity among strains. Clustering of PCR MP fingerprinting data matched with rep‐PCR fingerprinting data. The generated distribution tree showed that Tunisian isolates were closely related to the citrus reference strain LMG5496. In contrast, EC112, isolated from citrus, and the almond isolate EC122 were distantly related to the type strain LMG1247T isolated from lilac. Such studies have not been reported until now for P. syringae from citrus.

Bacterial etiology of necrotic spots on leaves and shoots of grapevine (Vitis vinifera L.) in Poland

“…The lack of one or two genes can be explained by their absence or a mutation in the genes that did not allow for their amplification (Ferrante et al 2015). In contrast to our results, in the studies of Abbasi et al (2013), Gilbert et al (2009), and Abdellatif et al (2017) all Pss strains had the syrB gene. This gene was also identified in the majority of Pss strains in studies of Scortichini et al (2003), although (weakly) pathogenic strains from zucchini, magnolia and avocado also lacked the gyrB gene Renick et al (2008) detected the syrD gene only in approximately 60% of pathogenic Pss strains.…”

Phylogenetic, genetic, and phenotypic diversity of Pseudomonas syringae pv. syringae strains isolated from citrus blast and black pit in Tunisia

“…However, EC20, EC33, EC201, EC229, and LMG5496 clustered in separate groups, while EC112 and EC122 clustered separately. The clustering based on the concatenated dataset was similar to one previously determined and published using rep‐PCR analysis on the same set of Pss strains (Abdellatif et al ., 2017).…”

“…Of them, two strains originated from C. sinensis (orange), 40 from C . limon (lemon), and one from Prunus amygdalus (almond; Abdellatif et al ., 2017). Additionally, one strain, LMG5496, isolated from C .…”

“…For MLSA, 13 out of the 42 Tunisian Citrus strains, the Tunisian almond strain, and the LMG5496 Citrus strain from Greece (15 in total) were selected as representatives of 10 previously distinguished clades, based on dendrograms generated from fingerprinting profiles from rep‐PCR and PCR‐MP (Abdellatif et al ., 2017).…”

“…To date, the genetic diversity of the P. syringae populations from Citrus crops remains poorly studied. Recently, in Tunisia, we reported the occurrence of Pss causing bacterial blast and black pit of orange and lemon (Abdellatif et al ., 2015, 2017). This pathogen was also reported on mandarin in Montenegro by Ivanović et al .…”