Studies on the transmission of the sugar beet disease syndrome of ‘basses richesses’ by insect vectors
In France, a new disease of sugar beet of complex etiology and called ‘syndrome des basses richesses’ was first observed in Bourgogne in 1991 (EPPO RS 2002/017 and 2002/084). A similar syndrome was also reported from Hungary in 2005 (EPPO RS 2006/085). The disease is mainly characterized by low sugar content in the roots of affected plants. Earlier studies have revealed the presence of a stolbur phytoplasma (‘Candidatus Phytoplasma solani’) and a bacterium-like organism related to ‘Candidatus Phlomobacter fragariae’* (herein called SBR bacterium for convenience) in diseased sugar beet plants. It has also been shown that an insect vector which was first identified as Pentastiridius beieri but now confirmed as Pentastiridius leporinus (Homoptera: Ciixidae) might be involved in disease transmission. Further studies have been carried out in France to clarify the role of three planthopper species living near or within sugar beet fields in spreading the two pathogens. The following leafhopper species were studied: Cixius wagneri, Hyalesthes obsoletus and P. leporinus (Homoptera: Ciixidae). As a result, P. leporinus was considered to be the economic vector of the syndrome of ‘basses richesses’ based on its abundance and high frequency of infection with the SBR bacterium. C. wagneri which has been demonstrated to transmit ‘Ca. Phlomobacter fragariae’ to strawberry was also found to be infected with the SBR bacterium and able to transmit it to sugar beet, however it is considered as a secondary vector. Neither C. wagneri nor P. leporinus were infected by ‘Ca. Phytoplasma solani’. Populations of H. obsoletus (a known vector of ‘Ca. Phytoplasma solani’) living on weeds (Convolvulus arvensis and Urtica dioica) did not carry the SBR bacterium but were highly infected with two distinct isolates of ‘Ca. Phytoplasma solani’. In transmission assays, only the phytoplasma isolated from C. arvensis was transmissible and pathogenic to sugar beet.
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* ‘Candidatus Phlomobacter fragariae’ is a γ-3 proteobacterium associated with marginal chlorosis of strawberry in western France.
Sources
Bressan A, Sémétey O, Nusillard B, Clair D, Boudon-Padieu E (2008) Insect vectors (Hemiptera: Cixiidae) and pathogens associated with the disease syndrome ‘Basses Richesses’ of sugar beet in France. Plant Disease 92(1), 113-119.