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07 November 2019 | Story Leonie Bolleurs | Photo Johan Roux
Prof Zakkie Pretorius
Prof Zakkie Pretorius, Research Fellow at the UFS Department of Plant Sciences.

Prof Zakkie Pretorius, Research Fellow, and Prof Botma Visser, Associate Professor, both from the Department of Plant Sciences at the University of the Free State (UFS), partnered in a ground-breaking research project headed by Dr Melania Figueroa from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia. Together, these scientists solved a 20-year-old mystery, uncovering the origins of one of the world’s deadliest strains of cereal rust disease.

The manuscript, with the title, Emergence of the Ug99 lineage of the wheat stem rust pathogen through somatic hybridisation, was accepted for publication in Nature Communications.

According to a statement released by CSIRO, research shows that the devastating Ug99 strain of the wheat stem-rust fungus was not the result of a sexual cross between different rust strains as previously thought, but in fact was created when fungal strands simply fused to create a new hybrid strain.

This process is called somatic hybridisation and enables fungi to merge their cells and exchange genetic material without going through a complex sexual reproduction cycle. The study found that half of Ug99’s genetic material came from a strain that occurred in Southern Africa around 100 years ago and eventually spread to Australia.

The discovery implies that other crop-destroying rust strains could hybridise elsewhere with Ug99, for example, to exchange genetic material and create a whole new enemy.

While there was some speculation that rust strains could hybridise – based on laboratory studies in the 1960s as well as some earlier studies on the topic – this comprehensive research now provided the first genomic evidence that the process can generate new strains.

History of Ug99

Prof Pretorius was the first person to describe the dangerous Ug99 isolate, confirming the ability of the isolate to leave the Sr31 resistance gene ineffective (up to that time, effective against all known wheat stem-rust races). This laid the basis for international concern.

He named the field sample Ug99, based on the country of origin (Uganda) and year of sample collection (1999). 

“The Sr31 resistance gene and associated traits were so effective that the gene occurred in almost 70% of CIMMYT’s (Mexican-based International Maize and Wheat Improvement Center) spring wheat germplasm. In addition, many popular cultivars containing the gene were released around the world.”

“Ug99 then disappeared for a few years. When the race re-appeared in East Africa, it caused localised but severe epidemics,” he said.

Prof Pretorius continues: “Leading wheat breeders and pathologists were concerned that Ug99 could destroy wheat production in many global regions where wheat is critical for food security. Thus, in 2005, Dr Norman Borlaug, Nobel laureate and father of the green revolution, called for a meeting in Kenya where a global effort to combat the threat was initiated. The international wheat research community was mobilised and with funding primarily from the Bill and Melinda Gates Foundation and coordinated by Cornell University in the USA, research commenced.”

wheat stem rust

Wheat stem rust 14: Rust diseases are the cause of extensive crop losses each year. With this recent discovery, published in 
Nature Communications, scientists can now better identify the resistance genes which can be bred into wheat varieties to give crops 
long-lasting protection against rust. (Photo: Supplied) 

“From field trials in Kenya, it soon became apparent that 90% of the world’s wheat varieties were susceptible to Ug99. Although breeding and selection for resistance started in earnest, the pathogen adapted, gaining virulence for other previously effective resistance genes. At present, 13 races have been described within the Ug99 group occurring in 13 countries, mostly in Africa, but also in Yemen and Iran. Five of these races are present in South Africa, all confirmed by scientists from the UFS and ARC-Small Grain in Bethlehem. The original Ug99 has, however, never been detected in South Africa.”

Combined efforts

Rusts are common fungal diseases of plants. The spores of the fungus attach themselves to the stems and leaves of wheat plants and essentially suck the nutrients from the plant. Plants either die or produce shrivelled and low-quality grain. 

Group Leader at CSIRO, Dr Melania Figueroa, agrees that Ug99 is considered the most threatening of all rusts, as it has managed to overcome most stem rust-resistance genes used in wheat varieties.

“There is some good news, however; the better you know your enemy, the more equipped you are to fight against it. Knowing how these pathogens come about means we can better predict how they are likely to change in the future and better determine which resistance genes can be bred into wheat varieties to give long-lasting protection.”

Earlier this year, CSIRO worked with the University of Minnesota and the 2Blades Foundation to improve wheat resistance by stacking five resistance genes into the one wheat plant to combat wheat stem rust. 

The breakthrough came as Dr Figueroa’s group was sequencing Ug99 (then at the University of Minnesota), and at the same time a CSIRO team led by Dr Peter Dodds was sequencing Pgt21 in Australia (Pgt21 is a rust strain that was first seen in South Africa in the 1920s and believed to have been carried to Australia in the 1950s by wind currents). When the two groups compared results, they found that the two pathogens share an almost identical nucleus and therefore half of their DNA.

“This discovery will make it possible to develop better methods to screen for varieties with strong resistance to disease,” said Dr Figueroa.

Molecular fingerprinting

In addition to infection studies, molecular fingerprinting by members of the South African Ug99 race group led by Prof Botma Visser at the UFS, confirmed their genetic placement in context with Ug99 and other global stem rust races. The availability of the original Ug99 collection, along with other local rust isolates in long-term storage at the UFS, was essential to the success of the current research.

Despite the continued evolution of stem-rust variants, excellent progress has been made worldwide in the breeding of resistant wheat cultivars, including in South Africa. With funding from the Winter Cereal Trust, Dr Willem Boshoff, Senior Lecturer in the Department of Plant Sciences at the UFS, is responsible for the annual testing of all commercial wheat cultivars and advanced breeding lines for appropriate stem rust races.

Dr Melania Figueroa
Dr Melania Figueroa from the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Photo: Kate Langford

News Archive

Multi-disciplinary research approach at UFS
2005-10-25

UFS follows multi-disciplinary research approach with opening of new centre 

“A new way of doing business in necessary in the research and teaching of agriculture and natural sciences in South Africa.  We must move away from  departmentalised research infrastructures and a multi-disciplinary approach to research involving several disciplines must be adapted,” said Prof Herman van Schalkwyk, Dean:  Faculty of Natural and Agricultural Sciences at the University of the Free State (UFS).   

Prof van Schalkwyk delivered the keynote address during the launch of the Centre for Plant Health Management (CePHMa) at the Main Campus in Bloemfontein today (21 October 2005).  CePHMa is an initiative of the UFS Department of Plant Sciences.

According to Prof van Schalkwyk a tertiary institution must practice multi-disciplinary research to be a world-class research institution.  “It is difficult for researchers to admit that they do not know a lot about each other’s area of speciality.  It is therefore necessary for researchers to make a paradigm shift and to focus on inter-disciplinary co-operation.  To do this, we must encourage them to work together and to find a common language to communicate ideas en establish symbiotic relationships,” said Prof Van Schalkwyk.

“We tend to think that research is better and faster if it is specialised.  This is not true.  The new generation of scientists are young and they are trained to form a concept of the total system and not to focus on a specific area of speciality.  At the UFS we encourage this approach to research.  This was one of the main reasons for the establishment of CePHMa,” said Prof Van Schalkwyk.
CePHMa is the only centre of its kind in Africa and is established to extend the expertise in plant health management in South Africa and in Africa, to train experts in plant health and to conduct multi-disciplinary research about the health of agricultural crops.  

“CePHMa is a virtual centre comprising of ten disciplines applicable to crop production and crop protection,” said Prof Wijnand Swart, Chairperson of CePHMa during the opening ceremony.

“The UFS is the leading institution in Africa in terms of news crop development and manages three research programmes that concentrate on new crops, i.e. the New Crop Pathology Programme, the New Crop Development Programme and the Insects on New Crops Programme.  Other applied research programmes that are unique to the UFS are genetic resistance to rust diseases of small grain crops and sustainable integrated disease management of field crops,” said Prof Swart.

“Because the expected growth in population will be 80% in 2020 in sub-Saharan Africa, the future demands of food produce in Africa will be influenced.  Therefore research will in future be focused on ways to improve food security by employing  agricultural systems that are economically viable and environmentally sound,” said Prof Swart.

“Thorough knowledge of the concept of holistic plant health management is crucial to meet the challenge and it is therefore imperative that innovative crop protection and crop production strategies, with particular emphasis on plant health, be adopted.  This is why the Department of Plant Sciences initiated the establishment of CePHMA,” he said.

According to Prof Swart there is a shortage of expertise in plant health management.  “The UFS has shown the potential to address the demand of the sub-continent of Africa regarding expertise training and CePHMa is the leader in southern Africa to provide in this need,” he said.

The appropriateness and quality of training in plant health management is reflected in the fact that students from Ethiopia, Eritrea, Malawi, Uganda, Zambia, Ghana, Tanzania, Cameroon, Angola, Mozambique and Lesotho have already been trained or are in the process of being trained in at the UFS.

Scientists from CePHMa have forged partnerships with numerous national and international institutions including the Agricultural Research Council (ARC), various community trusts, seed, pesticide and agricultural chemical companies, in addition to overseas universities. 

Media release
Issued by: Lacea Loader
Media Representative
Tel:  (051) 401-2584
Cell:  083 645 2454
E-mail:  loaderl.stg@mail.uovs.ac.za
21 October 2005

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