̽��ֱ�� of Cambridge - John Carr

Of cabbages and cows: increasing agricultural yields in Africa

lw355 — Mon, 13 Feb 2017 11:17:32 +0000

̽��ֱ��humble cabbage, universally despised by British schoolchildren, has found unexpected popularity on another continent. But just as the people of Ghana have developed an appetite – and a market – for this leafy green, so too has something else: a virus carried by aphids that causes the cabbages to wilt and die

By contrast, a parasite that emaciates cattle across sub-Saharan Africa has been around for thousands of years but continues to take its toll on certain species of the animals it infects. Prominent ribs are the frequent hallmarks of trypanosomiasis – caused by the presence of a cunning parasite that evades the animal’s immune system by periodically changing its protein ‘coat’.

Meanwhile, farmers in Ethiopia are turning away from the traditional zebu cattle towards breeds that produce greater quantities of milk. As a result they are exposing their herds – and themselves – to increasing levels of tuberculosis (TB) that are brought about by intensified animal husbandry practices.

What links cabbages and cows are three programmes that hope to connect fundamental research with improving farm yields, and in so doing contribute to solving a looming pan-African problem. More than half of global population growth between now and 2050 is expected to occur in Africa. And more people means a requirement for more food.

Ethiopia, for example, has the largest livestock population in Africa but, with a growing population and increasing urbanisation, even its 53 million cattle are not enough. And now efforts to intensify farming in the country are bringing a significant health concern. “ ̽��ֱ��new breeds are more vulnerable than zebu to bovine TB,” explains Professor James Wood from Cambridge’s Department of Veterinary Medicine. “This may have health implications for those who work with and live alongside infected cattle, and also raises concerns about transmission to areas with previously low TB.”

Wood leads a £2.9 million research programme, ETHICOBOTS, which is looking at the feasibility of control strategies, including cattle vaccination. ̽��ֱ��programme combines partners in eight Ethiopian and UK institutions, and brings together veterinary scientists, epidemiologists, geneticists, immunologists and social scientists. “We need this mix because we are not only asking how effective strategies will be, but also whether farmers will accept them, and what the consequences are for prosperity and wellbeing.”

̽��ֱ��difference that increasing productivity can have on farmers’ livelihoods is not lost on an insect expert at the ̽��ֱ�� of Ghana, Dr Ken Fening, who is working on another food-related research project. Cabbages are not indigenous to the continent but have become a major cash crop for Ghanaian farmers and an important source of income for traders to markets and hotels.

“A good crop can bring in money to buy fertilisers and farm equipment, and also help to pay for healthcare and education for the family,” he says. Recently, however, fields of stunted, yellowing, wilting cabbages, their leaves curled and dotted with mould, have become an all too familiar and devastating sight for the farmers of Ghana.

From his field station base in Kpong, Ghana, Fening works closely with smallholder farmers on pest control strategies. Two years ago they started reporting that a new disease was attacking their crops. “It seemed to be associated with massive infestations of pink and green aphids,” says Fening, “and from my studies of the way insects interact with many different vegetables, I’m familiar with the types of damage they can cause.”

Farmers were typically seeing the total loss of their crops and he realised that the devastation couldn’t just be caused by sap-sucking insects. Despite no previous reports of viral diseases affecting cabbage crops in Ghana, the symptoms suggested a viral pathogen.

With funding through the CAPREx programme, Fening began work with Cambridge plant biologist Dr John Carr. ̽��ֱ��pair collected samples of cabbage plants in Ghana showing signs of disease, and also aphids on the diseased plants. Back in Cambridge, Fening used screening techniques including a type of DNA ‘fingerprinting’ to identify the aphid species, and sophisticated molecular biology methods to try to identify the offending virus.

“Aphids are a common carrier of plant-infecting viruses,” explains Carr, whose research is funded by the Biotechnology and Biological Sciences Research Council as part of the £16 million SCPRID (Sustainable Crop Production Research for International Development) initiative. “ ̽��ֱ��‘usual suspects’ are turnip mosaic virus and cauliflower mosaic virus, which affect cabbages in Europe and the US.”

“We found that two different species of aphids, pink and green, were generally found on the diseased cabbages,” says Fening. “It turned out this was the first record of the green aphid species, Lipaphis erysimi (Kaltenbach), ever being seen in Ghana.” ̽��ֱ��pink aphid was identified as Myzus persicae (Sulzer).

What’s more, the virus was not what Carr expected, and work is now ongoing to identify the culprit. ̽��ֱ��sooner it can be characterised, the sooner sustainable crop protection strategies can be developed to prevent further spread of the disease not only in Ghana, but also in other countries in the region.

Another researcher who hopes that eradication strategies will be the outcome of her research project is Dr Theresa Manful. Like Fening, she is a researcher at the ̽��ֱ�� of Ghana and a CAPREx fellow. She has been working with Cambridge biochemist Professor Mark Carrington on African animal trypanosomiasis.

̽��ֱ��trypanosome that causes the disease is carried by the tsetse fly, which colonises vast swathes of sub-Saharan Africa. “This is a major constraint to cattle rearing in Africa,” she explains. “Although trypanosomiasis is also a disease of humans, the number of cases is low, and the more serious concerns about the disease relate to the economic impact on agricultural production.”

Carrington has worked for a quarter of a century on the parasite that causes the disease. He understands how the organism evades the immune system of the animal by changing its coat proteins so as to remain ‘invisible’.

“When you first start working on these parasites you are enamoured with the molecular mechanisms, which we now know a huge amount about,” he says. “But then when you look at the effect on large animals like cows you realise that there is almost nothing known about the dynamics of an infection, and even whether an infection acquired at an early age persists for its lifetime.”

Manful and Carrington set about testing herds in Ghana. They discovered that several trypanosome species can be found in the cattle at one time and that nearly all cattle were infected most of the time.

For Manful, one of the important gains has been the ability to expand the research in Ghana: “I now have a fully functional lab and can do DNA extraction and analysis in Ghana – I don’t have to bring samples to Cambridge. We are teaching students from five Ghanaian institutions the diagnostic methods.” She and Carrington have been recently funded through a Royal Society Leverhulme Trust Africa Award to continue their work.

“Agriculture faces increasing challenges,” adds Carr. “Bioscience is playing a crucial part in developing ways to mitigate pest impact and reduce the spread of parasites.

“We want to ensure not only that every harvest is successful, but also that it’s maximally successful.”

ETHICOBOTS is funded under the Zoonoses and Emerging Livestock Systems (ZELS) programme, a research initiative in the UK jointly funded by six research council and government bodies. Dr Ken Fening and Dr Theresa Manful were funded by the Cambridge-Africa Partnership for Research Excellence (CAPREx) and ̽��ֱ��ALBORADA Trust, through the Cambridge-Africa Programme.

Images: top: cabbage aphids (credit: Dr Ken Fening); bottom: cattle in Ghana (credit: Dr Theresa Manful and Professor Mark Carrington).

To keep up to date with the latest stories about Cambridge’s engagement with Africa, follow #CamAfrica on Twitter.

Africa’s food requirements, along with its population, are growing fast. Three research programmes ask how a better understanding of viruses, parasites and the spread of disease can pave the way to improving agricultural yields.

A good crop can bring in money to buy fertilisers and farm equipment, and also help to pay for healthcare and education for the family

Ken Fening

Hendrik Terbeck

Greengrocer at Arusha Market

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Virus attracts bumblebees to infected plants by changing scent

fpjl2 — Thu, 11 Aug 2016 18:05:25 +0000

Plant scientists at the ̽��ֱ�� of Cambridge have found that the cucumber mosaic virus (CMV) alters gene expression in the tomato plants it infects, causing changes to air-borne chemicals – the scent – emitted by the plants. Bees can smell these subtle changes, and glasshouse experiments have shown that bumblebees prefer infected plants over healthy ones.

Scientists say that by indirectly manipulating bee behaviour to improve pollination of infected plants by changing their scent, the virus is effectively paying its host back. This may also benefit the virus: helping to spread the pollen of plants susceptible to infection and, in doing so, inhibiting the chance of virus-resistant plant strains emerging.

̽��ֱ��authors of the new study, published today in the journal PLOS Pathogens, say that understanding the smells that attract bees, and reproducing these artificially by using similar chemical blends, may enable growers to protect or even enhance yields of bee-pollinated crops.

“Bees provide a vital pollination service in the production of three-quarters of the world’s food crops. With their numbers in rapid decline, scientists have been searching for ways to harness pollinator power to boost agricultural yields,” said study principal investigator Dr John Carr, Head of Cambridge’s Virology and Molecular Plant Pathology group.

“Better understanding the natural chemicals that attract bees could provide ways of enhancing pollination, and attracting bees to good sources of pollen and nectar – which they need for survival,” Carr said.

He conducted the study with Professor Beverley Glover, Director of Cambridge ̽��ֱ�� Botanic Garden, where many of the experiments took place, and collaborators at Rothamsted Research.

CMV is transmitted by aphids – bees don’t carry the virus. It’s one of the most prevalent pathogens affecting tomato plants, resulting in small plants with poor-tasting fruits that can cause serious losses to cultivated crops.

Not only is CMV one of the most damaging viruses for horticultural crops, but it also persists in wild plant populations, and Carr says the new findings may explain why:

“We were surprised that bees liked the smell of the plants infected with the virus – it made no sense. You’d think the pollinators would prefer a healthy plant. However, modelling suggested that if pollinators were biased towards diseased plants in the wild, this could short-circuit natural selection for disease resistance,” he said.

“ ̽��ֱ��virus is rewarding disease-susceptible plants, and at the same time producing new hosts it can infect to prevent itself from going extinct. An example, perhaps, of what’s known as symbiotic mutualism.”

̽��ֱ��increased pollination from bees may also compensate for a decreased yield of seeds in the smaller fruits of virus-infected plants, say the scientists.

̽��ֱ��findings also reveal a new level of complexity in the evolutionary ‘arms race’ between plants and viruses, in which it is classically believed that plants continually evolve new forms of disease-resistance while viruses evolve new ways to evade it.

“We would expect the plants susceptible to disease to suffer, but in making them more attractive to pollinators the virus gives these plants an advantage. Our results suggest that the picture of a plant-pathogen arms race is more complex than previously thought, and in some cases we should think of viruses in a more positive way,” said Carr.

Plants emit ‘volatiles’, air-borne organic chemical compounds involved in scent, to attract pollinators and repulse plant-eating animals and microbes. Humans have used them for thousands of years as perfumes and spices.

̽��ֱ��researchers grew plants in individual containers, and collected air with emissions from CMV-infected plants, as well as ‘mock-infected’ control plants.

Through mass spectrometry, researchers could see the change in emissions induced by the virus. They also found that bumblebees could smell the changes. Released one by one in a small ‘flight arena’ in the Botanic Gardens, and timed with a stopwatch by researchers, the bees consistently headed to the infected plants first, and spent longer at those plants.

“Bees are far more sensitive to the blends of volatiles emitted by plants and can detect very subtle differences in the mix of chemicals. In fact, they can even be trained to detect traces of chemicals emitted by synthetic substances, including explosives and drugs,” said Carr.

Analysis revealed that the virus produces a factor called 2b, which reprograms genetic expression in the tomato plants and causes the change in scent.

Mathematical modelling by plant disease epidemiologist Dr Nik Cunniffe, also in the Department of Plant Sciences at Cambridge, explored how the experimental findings apply outside the glasshouse. ̽��ֱ��model showed how pollinator bias for infected plants can cause genes for disease-susceptibility to persist in plant populations over extremely large numbers of generations.

̽��ֱ��latest study is the culmination of work spanning almost eight years (and multiple bee stings). ̽��ֱ��findings will form the basis of a new collaboration with the Royal Horticultural Society, in which they aim to increase pollinator services for cultivated crops.

With the global population estimated to reach nine billion people by 2050, producing enough food will be one of this century’s greatest challenges. Carr, Glover and Cunniffe are all members of the Cambridge Global Food Security Initiative at Cambridge, which is involved in addressing the issues surrounding food security at local, national and international scales.

̽��ֱ��use of state-of-the-art experimental glasshouses at Cambridge Botanic Garden, and equipment at Cambridge and Rothamsted, was funded by the Leverhulme Trust.

Study of bee-manipulating plant virus reveals a “short-circuiting” of natural selection. Researchers suggest that replicating the scent caused by infection could encourage declining bee populations to pollinate crops – helping both bee and human food supplies.

Modelling suggested that if pollinators were biased towards diseased plants in the wild, this could short-circuit natural selection for disease resistance

John Carr

John Carr/Alex Murphy

Researcher Sanjie Jiang inside the 'flight arena' in the glasshouse of the Cambridge ̽��ֱ�� Botanic Garden.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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