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Although many Agrobacterium radiobacter strains have already been identified, only a few genomes of strains belonging to genomovar G4 have been sequenced so far. In this study, we report the first virulent genome sequence of Agrobacterium radiobacter strain tun 183, which is highly virulent to almond specie. The genome size was estimated to be 5.53 Mb, with 57.9%GC content. In total, 6486 genes encoding proteins and 61 genes encoding RNAs were identified in this genome. Comparisons with the available sequenced genomes of genomovar G4 as well as with other A. sp. were conducted, revealing a hexapartite genome containing circular and linear chromosomes in addition to two accessory plasmids and a tumor inducing plasmid (pTi) in strain tun 183. The phylogenetic analysis of recA gene clearly showed the clustering of tun 183 strain within genomovar G4, supporting the monophyly within this genomovar.

This study was conducted to understand the high incidence of viruses previously reported in Tunisian olive groves. Forty three cultivars, native and introduced, under different cultivation regimes, were sampled in Tunisia, one of the countries with the highest levels of olive viruses. All olive-infecting viruses were tested. Total nucleic acids were extracted from 280 olive trees and their use as template for RT-PCR resulted in several non-specific products. Alternatively, dsRNAs were also extracted and 229 sampled trees showed dsRNAs molecules, suggesting the presence of viruses. However, RT-PCR tests using dsRNA as template, allowed to identify viruses in 209 samples. Olive mild mosaic virus (OMMV), Olive latent virus 1 (OLV-1), Olive leaf yellow associated virus (OLYaV) and Tobacco necrosis virus D (TNV-D) were detected. OLYaV was the most prevalent (63.0%), followed by OLV-1 (42.9%), TNV-D (21.80%) and OMMV (9.50%). The highest infection levels were observed in the northwest and centre east regions of Tunisia. Native cultivars presented higher virus incidences, mostly due to the most widespread cultivars in Tunisia: Chemlali (87%), Chetoui (94%), Meski (94%). Among the introduced cultivars, Picholine, Arbequina and Koroneiki presented the highest virus levels (88%, 79% and 64%, respectively). Considerable differences in virus presence were observed in samples from olive trees under different modes of management where levels were significantly (p > 0.05) higher in intensive orchards, regardless of the region and cultivar. To our knowledge, this was the first time that OMMV and TNV-D were detected in Tunisia and that such a complete analysis was performed.

Three hundred and eighteen symptomatic potato samples were collected from the main potato growing provinces of Tunisia, in main and late season crops (respectively spring and autumn 2013). Double antibody sandwich ELISA (DAS-ELISA) was used to assess the presence of the five most common potato viruses [Potato virus A (PVA), Potato virus X (PVX), Potato virus Y (PVY), Potato leafroll virus (PLRV) and Potato virus S (PVS)]. According to ELISA results, the highest overall percentage of infected samples was observed in the late season (84.5%), in comparison to the main season (30.7%). PVY was dominant in all infected plots with detection rates ranging from 20% in the North region (main season) to 100% in Cap Bon (late season). PLRV was the second most detected virus, with 4.3% distributed in the North West and Sahel during the main season, but was not detected in the late season. PVX was found with even lower detection rates of 0.6% and 1.3% in main and late seasons, respectively. No infection by PVA or PVS was detected in these two periods. Positive PVX detection results were confirmed by Reverse Transcription PCR using total RNA extracted from infected leaves. The near-complete nucleotide sequences of three PVX isolates were determined using an Illumina MiSeq sequencer. Phylogenetic analyses on full genome sequences or on coat protein (CP) gene sequences show that Tunisian PVX isolates belong to low diversity clade I.