This document discusses two emerging potato pathogens in South Africa: soft rot enterobacteria (SRE) and root knot nematodes (RKN). It provides background on potato production in South Africa and identifies clean seed as crucial. The document then focuses on identifying SRE and RKN using PCR-based molecular methods. It discusses interactions between SRE and RKN, finding that RKN wounds increase SRE in potato plants. The document also screens potato cultivars for resistance to blackleg disease caused by SRE, identifying one resistant cultivar. It concludes by acknowledging further screening and studies are needed.

1. Soft Rot Enterobacteria and Root
Knot Nematodes:Two Emerging
Pathogens of Potatoes
Lucy Moleleki
University of Pretoria

2. Background
South African potato production is approximately 50 000 ha
◦ There are 16 potato producing regions
◦ The different sectors are seed, table, export and processing
Like other crops, potatoes are susceptible to many
pests and pathogens including fungi, nematodes, bacteria
and viruses.
Clean seed is crucial for successful potato production.
The advent of PCR-based methods in identification –
Focus on Root Knot Nematodes and Soft Rot
Enterobacteriaceae.

3. Root Knot Nematodes
(Meloidogyne spp)
• The ability to identify and distinguish these different species
is important for implementation of appropriate control
majors, crop rotations, resistant cultivars and for quarantine
purposes.
• Traditionally, Root knot nematodes are identified and
distinguished based on morphology, but this can be difficult
for non specialist
• Difficulty in identifying emerging highly virulent species such as
M. enterolobii
• Seed tubers may have low levels of RKN and no apparent
symptoms.
• There is a need for a sensitive, rapid and accurate method of
RKN detection and identification.

4. Soft rot enterobacteria (SRE)
Formerly known as Erwinia spp
The former E. carotovora has now been reclassified as
Pectobacterium spp and the former E. chrysanthemii is now Dickeya
spp.
There are five Pectobacterium species but the use of PCR based
methods has facilitated identification of new and novel species.
Dickeya spp are divided into six species and several pathovars, D.
solani is a highly aggressive new novel species that has now been
identified in Europe and Israel.
Therefore it is important to constantly utilise molecular based
techniques to screen for presence of these aggressive species.

5. Approach
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9. Interaction between SRE and RKN
Both RKN and SRE pose a significant threat to potato
production.
There are no effective chemical treatments for SRE
and systemic nematicides are being withdrawn from
the market.
It is likely that RKN populations will grow in the
rhizosphere.
Nematodes are known to form synergies and
complexes with other pathogens in the soil increasing
diseases incidences of those pathogens.

10. bacteria
• Rhizosphere interactions
• Nematodes are relatively large
• repeated thrusting causes wounds
and mechanical damage
• RKN also form complexes with other
pathogens
• RKN and Ralstonia solanacearum
• RKN and Alternaria alternata
• Increased disease severity

11. One of the challenges in establishing whether an interaction
exists between two pathogens is the dependence on symptoms
as a measure of such interactions
We developed fluorescent protein tagged strains of soft rot
enterobacteria to establish interaction with root knot
nematodes

13. RKN wounds increase SRE in planta

14. Potato resistance to SRE and RKN
Resistant cultivars for SRE and the RKN present a
desirable alternative over harmful chemicals
We screened potato cultivars for resistance to blackleg
disease
A B

15. C D
E
A B

16. Kubheka, G., Coutinho T., Moleleki N and Moleleki L (2013) Phytopathology
Accepted for publication http://dx.doi.org/10.1094/PHYTO-02-13-0049-R
F G
H I

17. Summary and concluding remarks
The use of PCR based detection systems indicated presences of two
Pectobacterium spp: More screening is still necessary
P. wasabiae and P. brasiliense
A comprehensive survey of RKN in potatoes identified five Meloidogyne
spp including the highly virulent M. enterolobii.
The interaction between RKN and SRE in vitro and in planta using
fluorescent tagged SRE was demonstrated. There is a need to study
interactions between RKN and other pathogens using a similar system.
A cultivar with resistance to blackleg was identified and differences in
colonisation of the SRE on the susceptible and resistant cultivars were
observed.
Trials to determine if this cultivar is resistant to RKN or combined
infections between RKN and SRE are ongoing.

18. Acknowledgements