First report of ‘Candidatus Liberibacter solanacearum’ and its vectors Bactericera trigonica and B. nigricornis in Tunisia
In 2014-2016 symptoms similar to those associated with the presence of ‘Ca. L. solanacearum’ (EPPO A1 List, Solanaceae haplotypes) 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). 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 and caused significant yield losses. Symptoms were observed both in fields sown with locally produced seed and imported seed. Laboratory analyses by real-time PCR on samples taken from carrot fields in Kairouan detected ‘Ca. L. solanacearum’ haplotypes D and E. this is the first time haplotypes D and E were detected co-infecting a carrot plant. Three samples taken from field for carrot seed production tested positive for haplotype D.
Surveys on vectors were conducted between May 2014 and April 2015 in the governorates of Kairouan, Zaghouan, Monastir, Manouba, Beja, Gafsa and Sousse and showed that Bactericera trigonica and B. nigricornis (both Hemiptera: Triozidae) were present in all symptomatic fields. The authors note that both species were not previously known to be present in Tunisia and consider that they are likely to be the vectors of ‘Ca. L. solanacearum’ as reported in other Mediterranean countries. Bactericera trigonica and B. nigricornis were also observed on other crops from the Apiaceae family as well as on tomato and potato.
The situation of ‘Candidatus Liberibacter solanacearum’ in Tunisia can be described as follows: Present, only on carrot crops (haplotypes D and E).
Sources
Ben Othmen S, Morán FE, Navarro I, Barbé S, Martínez C, Marco-Noales E, López MM (2018) ‘Candidatus Liberibacter solanacearum’ haplotypes D and E in carrot plants and seeds in Tunisia. Journal of Plant Pathology 100(2), 197–207. https://doi.org/10.1007/s42161-018-0045-7
Ben Othmen S, Abbes K, El Imem M, Ouvrard D, Rapisarda C, & Chermiti B (2018). Bactericera trigonica and B. nigricornis (Hemiptera: Psylloidea) in Tunisia as potential vectors of ‘Candidatus Liberibacter solanacearum’ on Apiaceae. Oriental Insects, 1–13. https://doi.org/10.1080/00305316.2018.1536003