‘Syndrome des basses richesses’ detected in Germany: addition to the EPPO Alert List
As reported in EPPO RS 2002/017, 2002/084, 2008/083, a new disease of sugar beet (Beta vulgaris) called ‘syndrome des basses richesses’ has emerged in Eastern France since 1991. Affected sugar beet roots present a reduction of sugar content leading in some cases to serious economic consequences for the growers. Similar symptoms were also locally described in Hungary in 2005. For a long time, the etiology of the disease remained unclear, although stolbur phytoplasma and an unknown proteobacterium both transmitted by ciixid insects were found to be associated with the disease. Recent studies have showed that the main pathogen associated with ‘syndrome des basses richesses’ was a γ-proteobacterium tentatively called ‘Candidatus Arsenophonus phytopathogenicus’ (most Arsenophonus species are usually insect endosymbionts and are rather rarely plant pathogens) and that stolbur phytoplasma only played a marginal role. It was also demonstrated that the main vector of the disease was Pentastiridius leporinus (Hemiptera: Cixiidae), although originally it was misidentified as P. beieri. Because the disease has recently been found in Germany, the Panel on Phytosanitary measures decided that the ‘syndrome des basses richesses’ should be added to the EPPO Alert List, although it is acknowledged that many aspects of the biology and epidemiology of this disease remain highly uncertain.
‘Syndrome des basses richesses’ – a disease of sugar beet associated with ‘Candidatus Arsenophonus phytopathogenicus’ and transmitted by Pentastiridius leporinus (Hemiptera: Cixiidae)
Why: ‘Syndrome des basses richesses’ is an emerging disease of sugar beet (Beta vulgaris). It is associated with a γ-proteobacterium ‘Candidatus Arsenophonus phytopathogenicus’ and transmitted by a planthopper, Pentastiridius leporinus (Hemiptera: Cixiidae). This disease was first found in Eastern France in 1991 but its etiology remained uncertain for a long period. Syndrome des basses richesses causes a reduction in the sugar content at the time of harvest, thus leading to significant economic losses for growers. Because this syndrome has recently been detected in Germany, the Panel on Phytosanitary measures decided to add it to the EPPO Alert List.
Where: The disease was first observed in Eastern France in 1991. So far, it has only been observed in the departments of Côte-d’Or, Saône-et-Loire (Bourgogne region), and Jura (Franche-Comté region). In Hungary, similar symptoms were observed in 2005. At that time, the presence of bacterium-like organisms was detected in the phloem of diseased sugar beet plants but no recent information could be found to confirm the presence of ‘Ca. A. phytopathogenicus’ in Hungary. In Germany, the ‘syndrome des basses richesses’ was first observed in 2009 in several sugar beet fields near Heilbronn (Baden-Württemberg) and ‘Ca. A. phytopathogenicus’ was detected in diseased plants. The presence of P. leporinus was also noticed in affected fields. So far, the disease has only been found in Heilbroon, but investigations are being carried out in Baden-Württemberg to determine the extent and impact of the disease in sugar beet production.
EPPO region: France (Côte d’Or, Saône-et-Loire, Jura), Germany (near Heilbronn in Baden-Württemberg), Hungary (symptoms only).
The insect vector, Pentastiridius leporinus, is considered to be distributed thoughout Europe, the Near East, Central and East Asia, and Northern Africa. From the literature, the following distribution list could be prepared.
EPPO region: Albania, Algeria, Armenia, Austria, Azerbaijan, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Poland, Portugal, Romania, Russia, Slovakia, Spain, Sweden, Switzerland, Tunisia, Turkey, Ukraine, United Kingdom.
Africa: Algeria, Tunisia.
Asia: Afghanistan, China, Iran, Kazakhstan, Kyrgyzstan, Mongolia, Turkmenistan.
On which plants: Sugar beet (Beta vulgaris).
Until recently, the vector P. leporinus, was only reported to live on common reed (Phragmites australis). But studies carried out in Eastern France have shown that this insect was also associated with cultivated plants such as sugar beet and wheat (Triticum aestivum). In Eastern France, P. leporinus has only one generation per year and spends most of its life cyle as terricolous nymphal stages. Adults can colonize, mate, and lay eggs on sugar beet plants. Nymphs hatch within 10 to 15 days and by feeding on sugar beet roots, they develop into second and third instars from August to October. After a winter diapause, nymphs complete their development during the following spring by feeding on the roots of winter wheat. Adults then emerge from wheat fields in summer (June/July) and migrate to neighbouring sugar beet fields. Although it is supposed that P. leporinus has been able to shift from wild host plants to sugar beet fields and adapt to sugar beet/wheat rotations, these wild hosts have not yet been identified in Eastern France.
Damage: Symptoms appear shortly before the crop is harvested (usually in September). They include yellowing and bending of old leaves accompanied by new growth of central leaves which appear chlorotic, lanceolated and asymetric. The bacterium systemically invades the phloem of sugar beet causing necrosis of the vascular bundles. The infected roots have lower sugar content (reduction of 2 to 4%). It is reported that this reduction of sugar content can have dramatic economic consequences for growers. For example, in 1992 the loss of income observed in Eastern France was of about 50% over 1000 ha. In 2004, the rate of affected plants in sugar beet fields varied from 15 to 100 % over 1 800 ha, but no estimation of crop losses was given.
Transmission: P. leporinus has been identified as the main vector of ‘Ca. A. phytopathogenicus’ in sugar beet fields. It transmits the pathogen in a persistant mode. It is suggested that the emergence of the ‘syndrome des basses richesses’ in Eastern France has been coincidental with the increasing populations of P. leporinus in sugar beet fields.
Pathway: Infectious insect vectors.
Possible risks: Sugar beet is an economically important crop in the EPPO region. Direct control of the bacterium is not possible but it has been observed in Eastern France that the reduction of the vector populations with different techniques, such as chemical insect control, crop rotation with barley, and reduced tillage significantly lowered the impact of the disease. An express PRA conducted by the German NPPO concluded that the ‘syndrome des basses richesses’ presented a high risk for Germany, although many uncertainties remained due the general lack of data. Finally, the whole picture is further complicated by the fact that ‘Ca. A. phytopathogenicus’ might also affect strawberry (Fragaria ananassa). It has recently been proposed that ‘Ca. A. phytopathogenicus’ was also the causal agent of strawberry marginal chlorosis. This disease of strawberry observed in France, Japan, and possibly Italy was initially thought to be associated with ‘Candidatus Phlomobacter fragariae’ and transmitted by Cixius wagneri (Hemiptera: Cixiidae). If it is further confirmed that the diseases of sugar beet and strawberry are caused by the same pathogen, this will add to the risk.
EPPO RS 2002/017, 2002/084, 2008/083, 2012/221
Panel review date: -
Entry date 2012-10
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