Disease Management


Dr. Glynnis Cook


Mr. Kobus Breytenbach, Ms. Chanel Steyn, Mrs. Rochelle de Bruyn, Ms. Muriel Rikhotso, Dr. Hano Maree, Dr. Rachelle Bester (CRI), Dr. Ronel Roberts (ARC), Dr. Elize Jooste (ARC)
Vegetative propagation by grafting carries the potential to disseminate pathogens that are present in budwood and include bacteria, viruses and viroids. Research is inherently linked to the requirements of the Citrus Improvement Scheme (CIS) to ensure supply of healthy propagation material to the industry, which is reliant on good diagnostic capabilities. Supply of pathogen free material, since the inception of the CIS, has limited the impact of graft-transmissible diseases on tree health and production.
However, in instances where pathogens are vectored by insects which occur endemically, further control strategies are required. Citrus tristeza virus (CTV) is naturally transmitted by aphids and a research focus is therefore placed on the CTV cross-protection programme to mitigate the effects of the virus. Viroids also remain problematic in commercial orchards due to mechanical transmission during normal cultivation practices and with the practice of top-working established trees with new cultivars. Research efforts are required to understand the impact of viroids on tree growth and production and specifically the effects on various rootstocks. Additionally, new technologies such as high throughput sequencing and bioinformatics are applied to investigate diseases of unknown aetiology and pathogen diversity with the aim of improving diagnostic capabilities.



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