biology

Ug99

Ug99 is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ug99 rather than just read about it. In short: Ug99 is a lineage of wheat stem rust (Puccinia graminis f. sp. tritici), which is present in wheat fields in several countries in Africa and the Middle East and is predicted to spread rapidly through these regions and possibly further afield, potentially causing a wheat production disaster that would affect food security worldwide. In 2005 the noted green revolution pioneer Norman Borlaug brought great attention to…

Key takeaways

Ug99 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ug99 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ug99 from memory before moving on to harder problems.

Reference excerpt

Ug99 is a lineage of wheat stem rust (Puccinia graminis f. sp. tritici), which is present in wheat fields in several countries in Africa and the Middle East and is predicted to spread rapidly through these regions and possibly further afield, potentially causing a wheat production disaster that would affect food security worldwide. In 2005 the noted green revolution pioneer Norman Borlaug brought great attention to the problem, and most subsequent efforts can be traced to his advocacy. It can cause up to 100% crop losses and is virulent against many resistance genes which have previously protected wheat against stem rust. Although Ug99-resistant varieties of wheat do exist, a screen of 200,000 wheat varieties used in 22 African and Asian countries found that only 5–10% of the area of wheat grown in these countries consisted of varieties with adequate resistance. The original race of Ug99, which is designated as 'TTKSK' under the North American nomenclature system, was first detected in Uganda in 1998 and first characterised in 1999 (hence the name Ug99) and has since been detected in Kenya, Ethiopia, Eritrea, Sudan, Yemen, Iran, Tanzania, Mozambique, Zimbabwe, South Africa, and Egypt. There are now 15 known races of Ug99. They are all closely related and are believed to have evolved from a common ancestor, but differ in their virulence/avirulence profiles and the countries in which they have been detected.

Genetics Ug99 is the product of a type of somatic nuclear exchange event which has not been observed in other stem rust races. During this event and thereafter the nuclei have not experienced recombination.

Gene resistance Ug99 and its variants differ from other strains of the Black Stem Rust (BSR) pathogen due to their ability to overcome resistance genes in wheat that have been durable against the BSR pathogen for decades. These resistant Sr genes, of which 50 are known, give wheat different resistances to stem rust. The virulence in Uganda was virulent against Sr31 and is specific to Ug99. The massive losses of wheat that have occurred have been devastating, but in recent years the wheat rust epidemic has been effectively controlled through selection and breeding for additional Sr genes. (In the decades since, however, Sr31-virulence has evolved in other strains in other locations. Patpour et al., 2022 finds it in Spain and Siberia.) United States Department of Agriculture (USDA) researchers are testing genes to determine their Ug99 resistance, which will ultimately aid in the development of wheat varieties that will be able to fight off the rust. Resistance has been identified in a small number of spring wheat land races from North America – 23 out of 250 races with adult plant resistance, 27 out of 23,976 SNPs conveying APR, and only 9 races having seedling resistance. This resistance was present without the Ug99 pathogen challenge being present in NA to drive its selection. USDA has studied winter wheat land races where resistance is more probable. In addition to the research being conducted by the USDA, The United Kingdom's Department for International Development (DFID) along with Bill & Melinda Gates Foundation, announced in February 2011 that they will be granting $40 million to a global project led by Cornell University to combat virulent strains of Ug99. The five-year grant to the Durable Rust Resistance in Wheat (DRRW) project supported attempts to identify new resistance genes as well as reproduce and distribute rust resistant wheat seeds to farmers. There has been a continuous process of development of new resistant cultivars and failure of those cultivars. This demonstrates the need for continuous improvement. As of 2020 modern molecular and molecular genetics techniques are identifying quantitative trait loci (QTLs), particular cellular structures, and individual R genes more efficiently than ever before. These will be needed given the continuing severe, worldwide threat Ug99 poses. Sr35 confers resistance to all other severe Pgt races and the original Ug99. Salcedo et al., 2017 finds its Avr target, AvrSr35. Races virulent on Sr35 benefit from nonfunctionalization of AvrSr35 by insertion of a mobile element.

Races There are 15 races of Ug99, which (under the North American nomenclature system) have the designations TTKSK, TTKSF, TTKST, TTTSK, TTKSP, PTKSK, PTKST, TTKSF+, TTKTT, TTKTK, TTHSK, PTKTK, TTHST, TTKTT+, and TTHTT. They are all closely related and are believed to have evolved from a common ancestor.

TTKSK Also known as PTKS. The first Ug99 race to be characterised. Like most Ug99 races, and unlike other stem rust varieties, it is virulent against the Sr gene Sr31; also virulent against Sr38. Avirulent against Sr24. It was found in Uganda in 1999, Kenya in 2001, Ethiopia in 2003, Sudan and Yemen in 2006, Iran in 2007, and Tanzania in 2009, Eritrea in 2012, and Rwanda and Egypt in 2014.

TTKSF First detected in South Africa in 2000, Zimbabwe 2009, and Uganda in 2012. Avirulent on Sr31.

TTKST Discovered in Kenya in 2006 was the first Ug99 race found to be virulent against Sr gene Sr24. TTKST is now the predominant stem rust race in Kenya. Virulent on Sr31.

TTTSK First detected in Kenya in 2007, Tanzania in 2009, Ethiopia in 2010, Uganda in 2012, and Rwanda in 2014. Virulent on Sr31 and Sr36.

TTKSP First detected by Visser et al., 2011 in South Africa in 2007. Avirulent on Sr31 and virulent on Sr24.

PTKSK First detected in Ethiopia in 2007, Kenya in 2009, Yemen in 2009, and South Africa in 2017. Virulent on Sr31 and avirulent on Sr21.

PTKST First detected in Ethiopia in 2007, Kenya in 2008, South Africa in 2009 by Visser et al., 2011, Eritrea and Mozambique and Zimbabwe in 2010. Virulent on Sr31 and Sr24, but avirulent on Sr21.

TTKSF+ First detected in both South Africa and Zimbabwe in 2010. Virulent against Sr9h. Avirulent on Sr31 but virulent on Sr9h.

TTKTT First detected in Kenya in 2014. Also detected in Iraq in 2019, the first such detection in the country. Found in Nepal in 2023. Virulent on Sr31, Sr24, and SrTmp.

TTKTK First detected in Kenya, Rwanda, Uganda, Eritrea, and Egypt in 2014. Virulent on Sr31 and SrTmp.

TTHSK First detected in Kenya in 2014. Differs from the original (TTKSK) by avirulence against Sr30. Similar to TTHST. Virulent on Sr31 but avirulent on Sr30.

PTKTK First detected in Kenya in 2014. Differs from PTKSK by virulence against SrTmp. Differs from TTKTK by avirulence against Sr21. Virulent on Sr31 and Sr24, but avirulent on Sr21.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Ug99

Start with the simplest possible case. Write down what Ug99 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ug99 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ug99 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ug99

In research: Ug99 appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ug99 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ug99 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fungal plant pathogens and diseases, Puccinia, Wheat diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Ug99 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Ug99 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ug99 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ug99 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ug99 in simple terms?

Why does Ug99 matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ug99?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ug99.