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THE PLANT BIOTECHNOLOGY PROGRAMME
CASSAVA RESEARCH PROGRAM
Cassava in the southern and eastern African context
Cassava (Manihot esculenta) is the fourth most important food crop in the sub-tropical regions of the world. Cassava is currently grown in South Africa (SA) as a food security crop by subsistence farmers and also commercially for starch. The potential for biofuels is also realized. Cassava mosaic disease (CMD) is endemic in SA and several geminivirus species, SACMV, ACMV and EACMV have been reported in SA. South African cassava mosaic virus (SACMV) was first described in 1997 in SA and has since been discovered in Zimbabwe and Madagascar. Furthermore, the recent discovery of satellite DNA molecules associated with EACMV in Tanzania, open up new frontiers in helper virus-satellite-host interactions.
Our laboratory is engaged in research to improve cassava germplasm with regards to CMD and whitefly resistance. In addition, we are involved in studying the biodiversity, evolution and epidemiology of cassava begomoviruses and whitefly vectors in southern Africa. We are working in collaborations with countries such as Switzerland, Mozambique, Tanzania and Uganda in developing cassava for the southern African region, and building capacity for cassava transformation. Our sponsors for this research are multiple, but include the Technical Innovation Agency, National Research Foundation and Casquip Cassava Starch Manufacturing Company.
Transgenic plants using pathogen-derived resistance
Our objectives:
Select and optimize various size constructs from different ORFs of SACMV, ACMV and EACMV to design
RNA silencing cassettes for Pathogen Derived Resistance.
Test a Defective Interfering molecule from SACMV for disease amelioration
Test antisense constructs for SACMV silencing efficiency
Genetic transformation and regeneration of cassava
Our objectives :
Establish routine transformation and regeneration protocols of commercially grown or selected cassava cultivars
Optimization of Agrobacterium transformation of cassava
Test alternate plant transformation vectors
Test antibiotic-free selection markers minimal cassettes
Determination of suitable explants to use for direct regeneration
Optimize cassava inoculation with various techniques such as biolistics and agroinfection
Molecular methodology for characterization of transgenics
Acclimatization of transgenic plants to greenhouse and field conditions
Biodiversity Studies of Whitefly Vectors and Begomoviruses of Cassava
Our Objectives:
Epidemiological surveys of whitefly biotypes and cassava begomoviruses in South Africa and Mozambique
Whitefly genotyping using mtCOI gene in collaboration with Prof. Judy Brown
Cassava virus biodiversity using RFLPs, Rolling circle amplification (RCA), and differential PCR and sequencing
Screening for possible recombination among CMGs
Screening for satellite DNAs associated with EACMV and EACMCV
Expression of episomal and integrated satellite DNAII and III
Host Responses to SACMV Infection
Our objectives:
Using gene expression profiling methods (DNA microarrays, Illumina or SoLID genome sequencing platforms) to identify host genes in cassava governing resistance and susceptibility in response to SACMV infection
Developing potential genes as markers for disease identification
Validation of potential candidate genes through genetic complementation experiments or VIGS
Elucidating mechanisms involved in susceptible host-virus interactions in the model plant system A.thaliana and N. benthamiana
TOMATO RESEARCH PROGRAM
Tomato in the southern African context
Tomato (Solanum lycopersicum or Lycopersicon esculentum) is a herbaceous, dicotyledonous perennial plant which is grown in most countries around the world. Global annual production of tomatoes reached 130 million tons in 2008 (FAOSTAT, 2008). In southern Africa, tomato is considered as one of the most important vegetables along with potatoes and onions. It is grown mainly by subsistence farmers, and the majority of tomato trade in southern Africa, including SA, occurs largely in the informal sector. A third of the total national SA production in supplied by the tomato processing industry. Tomatoes are regularly consumed along with maize meal, which is considered the major staple of southern Africans.
Tomatoes are highly sensitive to attack by a wide variety of pathogens in the field largely due to its cultivation during spring and summer months which favour the growth and transmission of numerous pathogens. These biotic stresses cause mass destruction to tomato plantations leading to substantial economic losses. Control methods such as fungicides, roughing, crop rotations and insecticides have proven to be inefficient in controlling these pathogens. As a result farmers have turned to the use of resistant varieties combined with stringent chemical and heat pre-treatment of seeds before sowing.
a) Of particular interest to our plant biotechnology research group is the detection and control of pathogens, in particular viruses. The novel geminivirus pathogen Tomato curly stunt virus (ToCSV) was recently discovered in SA and Mozambique and our group is currently conducting research, in collaboration with SAKATA Vegenetics (RSA), the University of Johannesburg, University of Pretoria and University of Eduardo Montlane (Mozambique) in the following:
Epidemiology of ToCSV in SA and Mozambique
Biodiversity of viruses and whitefly vector
ToCSV resistance studies and molecular markers
b) Development of a diagnostic tool that demonstrates high reliability, sensitivity and specificity for a range of pathogens in
tomato. In particular, Multiplex PCR and micoarrays are being explored to increase the number of detected pathogens in tomato
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CONTACTS: Prof. Chrissie Rey 011 717 6324 or 082 499 5790 Chrissie.Rey@wits.ac.za
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