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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

Ensure your place at the UFS
2010-10-27

The University of the Free State (UFS) appeals to all prospective South African students who want to come and study at the UFS in 2011 to submit their applications no later than Tuesday, 30 November 2010.

The UFS is aware of the fact that learners will not have received their final Grade 12 results by Tuesday, 30 November 2010; therefore provisional admission will be granted based on learners’ most recent Grade 12 results. Final admission will take place upon receipt of the final Grade 12 results, which will be available early in January 2011.

Prospective students can obtain application forms for admission at the following places:

  1. The UFS’s web site at www.ufs.ac.za,
  2. The Information Office (Unit for Prospective Students) at the Thakaneng Bridge on the UFS’s Main Campus in Bloemfontein,
  3. You may also send an e-mail to info@ufs.ac.za or
  4. Phone 051 401 3000 and the necessary forms will be posted to you.

Senior undergraduate students (that is all students who were registered up to and during 2010 at the UFS) as well as post-graduate students, must self-register electronically on-line from Monday, 1 November 2010 until Tuesday, 4 January 2011. This includes master’s and doctoral students.

In order to encourage senior students to register online, the UFS offers 20 laptops as incentives for the senior students who successfully register online from 1 November 2010. These laptops will be handed over to the winners after the registration process in 2011.

Registration of first-year students:

The Rector and Vice-Chancellor, Prof. Jonathan Jansen, will welcome first-year students on Friday, 14 January and Saturday, 15 January 2011, respectively, in the Callie Human Centre. The Faculties of Economic and Management Sciences, the Humanities and Education will be welcomed on 14 January 2011 and the students of the Faculties of Natural and Agricultural Sciences, Law and Theology shall be welcomed on 15 January 2011. The compulsory orientation programme for new first-years will also then commence.

From 17 to 21 January 2011 first-year students will receive academic advice at the Callie Human Centre, whereafter they will be referred for self-registration. These processes will take place according to the set timetable. This timetable is available in the Kovsie Guide that will be sent to learners as soon as we have received their applications, as well as on the web site of the UFS at www.ufs.ac.za/register2011.

First-year students’ fees must be paid prior to arrival on 14 and 15 January 2011.

Registration of senior students:

Senior students who experience problems with the electronic on-line self-registration process have the opportunity to resolve problems within a programme on campus from Wednesday, 5 January until Wednesday, 12 January 2011. This programme will be sent out to students and is also available at www.ufs.ac.za/register2011. The specific scheduled day for senior students to resolve problems is the last and only day to resolve the problem.

Senior students can also contact 051 401 9111 for more information in this regard.

Students may register for prescribed modules for 2011, even though the November 2010 examination results are not yet available. Changes resulting from examination results that are made available later can be done up to and including 28 January 2011.

In terms of applications for senior students, only students who have interrupted a calendar year of study need to re-apply for admission.

Registration of students at the UFS’s Qwaqwa Campus:

Senior and first-year students of the UFS’s Qwaqwa Campus register from Wednesday, 12 January until Friday, 28 January 2011 in the Nelson Mandela Hall on this campus.

Registration of students at the UFS South Campus:

First-year students from the UFS’s South Campus in the University Preparation Programme and the Extended Programme (only Natural and Agricultural Sciences) register from Monday, 24 January till Friday, 28 January 2011 in the Arena Hall on the South Campus.

Students who have successfully completed the University Preparation Programme register with the first-year students on the UFS Main Campus on Friday, 14 and Saturday, 15 January 2011 – according to faculties (cf. paragraph 6).

Lectures for all students shall commence on Monday, 24 January 2011.

MEDIA RELEASE
Issued by: Lacea Loader
Director: Strategic Communication (actg)
Tel: 051 401 2584
Cell: 083 645 2454
E-mail: loaderl@ufs.ac.za
26 October 2010

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