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Graft Transmissible Diseases

Programme Coordinator:

Glynnis Cook

Collaborating Researchers:

Kobus Breytenbach, Chanel Steyn, Dr. Hano Maree, Prof. Johan Burger, Ronel Roberts

Research Conducted: 

Research is inherently linked to the requirements of the Citrus Improvement Scheme (CIS) to ensure supply of healthy propagation material to the industry. Supply of good quality material since the inception of the CIS has limited the number of graft-transmissible diseases that challenge production. CTV and African Greening are the two pathogens that require management strategies for control as they are also transmitted by insect vectors. A strong research emphasis is therefore placed on the CTV cross-protection programme to mitigate the effects of this virus and also epidemiological aspects of African citrus greening disease. The effects that viroids may have on tree health and production are also investigated by testing the sensitivity of commercial rootstocks to certain viroid species.

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