Abstract
Vegetative disorders similar to those associated with the presence of ‘Candidatus Liberibacter solanacearum’ (CaLsol) were observed in carrot plants in Kairouan, Tunisia from 2014 to 2016. Symptoms including leaf curling, yellowing, bronze and purplish discoloration, stunting of plants and roots, and proliferation of secondary roots, affected 20 to 40% of the carrots in some plots. In order to determine if these symptoms were associated with the presence of CaLsol, and/or ‘Ca. Phytoplasma spp.’ and/or Spiroplasma citri, real-time PCR analyses were conducted using specific primers for these pathogens. CaLsol was detected for the first time in Tunisia and for the first time its haplotypes D and E were detected co-infecting a carrot plant. Furthermore, three samples of carrot seed produced in Kairouan tested positive for the haplotype D, showing a high percentage (35 to 63%) of viable bacterial cells after treatment with propidium monoazide. However, all the tests were negative for ‘Ca. Phytoplasma’ spp. as well as for S. citri. The results highlight that several CaLsol haplotypes are emerging carrot pathogens in new areas.
Highlights
Carrot is one of the most important crops in Tunisia
Many negative and positive samples were tested by the Teresani et al (2014) assay, or with the Plant Print kit with the same results, with the exception of eight clear positive samples by Li et al (2009) that were only detected by Teresani et al (2014) in late cycles
The emerging bacterium Ca. L. solanacearum’ (CaLsol) is associated with socioeconomically important diseases in many crops (Munyaneza 2012; Haapalainen 2014)
Summary
Carrot is one of the most important crops in Tunisia. The average production is about 215,000 tons per year, from an area of 6319 ha (http://www.agriculture.tn, dates from 2015). The main production area of approximately 1730 ha is located in the centre of the country (Governorate of Sidi Bouzid). In 2014, 2015 and 2016, symptoms similar to those associated with the presence of ‘Ca. L. solanacearum’ (CaLsol) were observed in the Governorates of Kairouan and Sidi Bouzid and, to a lesser extent, in several other carrot-growing areas such as Fahes (Governorate of Zaghouan) and Chott-Mariem (Governorate of Sousse). There were around 20% symptomatic plants during 2014, that. S. Ben Othmen and F.E. Morán are first authors
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