SBR & RTD

SBR & RTD: Two new challenging diseases for sugarbeet

The two new sugarbeet diseases SBR ("Syndrome Basses Richesses"/syndrome of low sugar content) and RTD (Rubbery Taproot Disease) pose major challenges for sugarbeet growers and the sugar industry. 

Both diseases SBR and RTD are caused by different bacterial pathogens. The SBR disease is associated as major pathogen with a Proteobacterium 'Candidatus Arsenophonus phytopathogenicus' and as minor pathogen with a Phytoplasma 'Candidatus Phytoplasma solani' (stolbur phytoplasma). The RTD disease is mainly associated only with the Phytoplasma 'Candidatus Phytoplasma solani' (stolbur phytoplasma). These bacterial pathogens are transmitted by different species of planthoppers. The major occurrence of the different planthoppers species varies across different regions of Europe.
Plants infested with SBR show yellowed leaves that can be seen across the entire field. The vascular bundles are colored brown, which becomes visible when the storage root is cut. New leaves are formed which are asymmetrically shaped. In addition, the sugar content is significantly reduced.
In the case of RTD disease, the leaves first turn yellow, wilt and subsequently die. The storage root starts to become rubbery. In case of strong infestation, the storage root can also start to rot. RTD removes water from the storage root, therefore the sugar content is not reduced as with SBR disease. However, sugarbeet yields are heavily reduced. In addition, the sugarbeet can hardly be stored and can also lead to processing problems in the factory.

Syndrome des Basses Richesses (SBR)

Symptoms:

Yellowing of leaves (wide area across field)
Abnormal leaf regrowth (lancet leaves)
Brownish vascular discoloration
Reduced sugar content (up to 5% lower)
Reduced root yield (up to 30% lower)

Main vector:

Pentastiridius leporinus (Schilf-Glasflügelzikade)

Major pathogen:

Ca. Arsenophonus phytopathogenicus

Minor pathogen:

Ca. Phytoplasma solani

Rubbery Taproot Disease (RTD)

Symptoms:

Yellowing of older leaves
Wilting, necrosis and dying of leaves (abnormal leaf re-growth)
Root tissue like rubber –> effect on storage and processing
Coincidence with biotic and abiotic stress
Strong reduction of root yield
Secondary infection with e.g. Macrophomina phaseolina possible as a consequence of RTD infection

Vectors:

Reptalus quinquecostatus (Pfriemen-Glasflügelzikade)
Hyalesthes obsoletus (Winden-Glasflügelzikade)
Pentastiridius leporinus (Schilf-Glasflügelzikade)

Main pathogen:

Ca. Phytoplasma solani
The pathogen is not unknown !!!
Rubbery Taproot Disease (RTD) „Gummirüben“ / Serbia in 2021, Ćurčić et al. (2021) 

Comparison of symptoms

Symptom	Syndrome Basses Richesses (SBR)	Rubbery Taproot Disease (RTD)
Drought symptom	-	+
Rubbery tissue	-	+
Yellowing leaves	+	(+)
Abnormal leaf shape/regrowth	+	-
Symptoms on vascular bundles	+	-