Soft Rot Enterobacteria and Root Knot Nematodes: Two Emerging Pathogens of Potatoes

Lucy MolelekiUniversity of Pretoria

BackgroundSouth 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 manypests and pathogens including fungi, nematodes, bacteriaand viruses.

Clean seed is crucial for successful potato production.

The advent of PCR-based methods in identification –Focus on Root Knot Nematodes and Soft RotEnterobacteriaceae.

Root Knot Nematodes (Meloidogyne spp)• The ability to identify and distinguish these different species

is important for implementation of appropriate controlmajors, crop rotations, resistant cultivars and for quarantinepurposes.

• Traditionally, Root knot nematodes are identified anddistinguished based on morphology, but this can be difficultfor non specialist• Difficulty in identifying emerging highly virulent species such as

M. enterolobii

• Seed tubers may have low levels of RKN and no apparentsymptoms.

• There is a need for a sensitive, rapid and accurate method ofRKN detection and identification.

Soft rot enterobacteria (SRE)Formerly known as Erwinia spp

The former E. carotovora has now been reclassified asPectobacterium spp and the former E. chrysanthemii is now Dickeyaspp.

There are five Pectobacterium species but the use of PCR basedmethods 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 beenidentified in Europe and Israel.

Therefore it is important to constantly utilise molecular basedtechniques to screen for presence of these aggressive species.

Approach

mdh gapA

genebank

Interaction between SRE and RKNBoth RKN and SRE pose a significant threat to potatoproduction.

There are no effective chemical treatments for SREand systemic nematicides are being withdrawn fromthe market.

It is likely that RKN populations will grow in therhizosphere.

Nematodes are known to form synergies andcomplexes with other pathogens in the soil increasingdiseases incidences of those pathogens.

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

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

RKN wounds increase SRE in planta

Potato resistance to SRE and RKN

Resistant cultivars for SRE and the RKN present adesirable alternative over harmful chemicals

We screened potato cultivars for resistance to blacklegdisease

A B

C D

E

A B

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

Summary and concluding remarksThe use of PCR based detection systems indicated presences of twoPectobacterium spp: More screening is still necessary

P. wasabiae and P. brasiliense

A comprehensive survey of RKN in potatoes identified five Meloidogynespp including the highly virulent M. enterolobii.

The interaction between RKN and SRE in vitro and in planta usingfluorescent tagged SRE was demonstrated. There is a need to studyinteractions between RKN and other pathogens using a similar system.

A cultivar with resistance to blackleg was identified and differences incolonisation of the SRE on the susceptible and resistant cultivars wereobserved.

Trials to determine if this cultivar is resistant to RKN or combinedinfections between RKN and SRE are ongoing.

Acknowledgements