Budwood

New cultivars are obtained from the discovery of mutations in orchards, the breeding programme at the Institute for Tropical and Subtropical Crops (ITSC) (previously known as the CSFRI) and the importation of promising cultivars from other countries. Since the deregulation of the citrus industry in 1997 private cultivar agents have also become involved in this process. The ITSC and the CRI facility in Nelspruit are responsible for shoot-tip grafting and pre-immunisation of material with a mild strain of Citrus Tristeza Virus. The Citrus Foundation Block is responsible for increase and release of propagation material to the citrus industry. The CRI Division of Cultivar Development is responsible for the introduction and commercialisation of new citrus cultivars to meet the changing requirements of the markets, and optimise accessibility of cultivars to Southern African producers. All promising cultivars are planted in suitable trial sites and evaluated by the Cultivar Evaluators. The CIS Advisory Committee is responsible for the co-ordination of these processes.

Phytosanitary quality of seed produces at CFB
In Table 2, various factors and actions are described to demonstrate the phytosanitary quality of seed from CFB. In order to put this very important aspect into context of safe trade of citrus seed, the citrus diseases regarded as seed transmissible are listed in Table 2 with scientific references and brief statement of its applicability to the South African and CFB context. Click here to view a summary of the pathogens proven to be seed transmissible.

Please note that other diseases and pests often of concern, such as Citrus Black Spot (CBS, caused by Guignardia citricarpa), Citrus nematode (Tylenchulus semipenetrans) and various citrus viroids, are not seed transmissible [Bitters, Brusca & Dukeshire (1954) Citrus Leaves 34: 8. (Cited by J.S. Semancik, http://www.dpvweb.net/dpv/showdpv.php?dpvno=226)]. Moreover, CFB is free from CBS as proven by annual surveys described in point 4 below. 

1. Location of Citrus Foundation Block (CFB)
The CFB is located in the Eastern Cape province of South Africa near Uitenhage in a secluded valley where citrus is not commercially grown. The nearest commercial citrus orchards are located in Kirkwood, which is approximately 40 km from the CFB. To preserve this secluded location, South Africa’s Department of Agriculture (DoA), which is the National Plant Protection Organisation of South Africa, endorsed a 5 km exclusion zone around the CFB in which no citrus trees are allowed to be grown, commercially or in home gardens.

2. All rootstock trees were planted virus-free
Regardless of its origin, any rootstock cultivar selected to be planted at CFB must first be proven virus free after shoot-tip grafting and subsequent diagnostic testing (including hard wood biological indexing, ELISA and/or PCR) before it is multiplied in vector-free tunnels and planted.

3. Preventative spray programmes
All citrus trees at CFB are subjected to a rigorous fungicide and pesticide spray programme aimed at prevention of fungal diseases and insect pests. Regular scouting is done in all tunnels and orchards to ensure the disease and pest-free status of the CFB.

4. Annual inspections
All trees in the CFB are inspected annually during the winter harvesting period (July – August) by technical experts from DoA and CRI, which includes plant pathologists, entomologists and horticulturists. Suspicious fruit or foliar symptoms are studied by this team of experts and should any uncertainty prevail, samples are subjected to molecular diagnostic procedures.

5. Postharvest treatment of seed
Fruit is harvested by means of hand picking. Seed is extracted by a seed extraction machine and immersed in hot water at 51.5°C for 10 minutes and thereafter dip-treated with 8-hydroxy-quinolene sulphate (Chinosol) at 15g/litre. This surface disinfection treatment prevents viral, bacterial or fungal contamination from unknown sources, and prolongs the storage life of seed. Treated seed are dried in the shade and hand sorted. Subsequently, it is packed in 1- or 2-litre plastic bags and stored at 10°C. Optionally, bulk orders are packed in larger containers.

More Information

Please feel free to contact the CFB Manager, Thys du Toit at tdt@cri.co.zav.