Research: Graft Transmissible Diseases

Programme Coordinator:
Glynnis Cook

Collaborating researchers involved:
Dr. Fanie van Vuuren, Kobus Breytenbach (CRI), Dr Hano Maree (SU, ARC), Prof Johan Burger (SU), Prof. Gerhard Pietersen (ARC, UP)

Research is mainly focused on African citrus greening and Citrus tristeza virus (CTV). African citrus greening disease, which is not as severe as Asiatic and American citrus greening, is potentially one of the most damaging diseases in South Africa but is kept at bay by controlling its vector, the citrus psylla, Trioza erytreae. CTV is spread by aphids and is managed primarily by the use of non-virulent cross protective CTV strains. Services in this project, largely involve diagnostics, disease surveys and ensuring the phytosecurity of the Citrus Improvement Scheme. The main aspects addressed through research and services are summarised below:

Cross Protection

  1. Identification and evaluation of CTV mild strains for use as pre-immunising agents
  2. Study sustainability of cross protection strategies

Etiology + Diagnosis

  1. Develop molecular detection techniques for rapid detection and diagnosis of local and exotic diseases
  2. Develop techniques to differentiate between CTV strains
  3. Characterise variability in pathogen populations
  4. Investigate the cross protection mechanism


  1. Study epidemiological aspects for implementation or improvement of management strategies


  1. Formulate identification, containment and eradication strategies in event of foreign pathogen incursion
  2. Formulate strategies to prevent across-border or within-border pathogen incursions
  3. Standard operating procedures to maintain phytosecurity of Citrus Improvement Programme
  4. Co-ordinate post-entry quarantine strategies with relevant authorities

Inoculum Management

  1. Formulation and evaluation of sanitation strategies that would limit spread of African citrus greening and CTV
  2. Implementation and optimisation of pathogen elimination strategies from propagation material

Host Resistance

  1. Identification and characterisation of host resistance

Curative control

  1. Develop chemical and/or physical curative control strategies against African citrus greening

Vector control

  1. Develop molecular techniques to monitor the "infectivity" of vector populations
  2. Collaborate with entomologists to formulate effective strategies to limit disease spread