Looking for solutions in Africa’s ‘orphan’ crop: sorghum

Leonie Joubert

Prof Bongani Ndimba stands in a sunny nook in the University of the Western Cape’s (UWC) new Life Sciences building. It’s mid-2010, and the winter sun is angling through the blades of ankle-high grass growing out of a seed tray at eye level on the silver shelves that line the wall-to-ceiling windows. The words ‘control’ is written in black pen, freehand, beneath the vigorous-looking grass to the left of the tray; ‘drought’ beneath the scraggly tufts on the right.

‘These plants are about two and a half weeks old. I’m drought stressing these,’ Ndimba says, pointing to the runty plants on the right, ‘and I’m watering these. This is small scale, but I’m testing this environment.’

Ndimba’s proteomics unit – which studies proteins in plants – moved into the state-of-the-art building in March that year, when he started growing different types of the indigenous African grass, sorghum, in a greenhouse-like alcove on the outer edge of the biotechnology department. Just two steel shelves with a few trays of plants, but part of a much bigger vision that has implications for how Africa feeds itself, particularly as climate change makes some parts of the continent more drought-stressed and rainfall less predictable.

The plan was to grow these plants  – some well watered, others drought-stressed – before getting down to the high-tech work: extracting tissue from the leaves of the plants and, using mass spectrometry, analyse the proteins  to see which might have something to do with a plant’s ability to withstand water stress.

‘There are proteins in the plants that assist the organism to tolerate drought. Those proteins are expressed more in drought-tolerant varieties of sorghum than in drought-susceptible varieties. So the idea of our work is to see which one of those proteins is most influential in the drought-tolerant status of the variety,’ he explains.

Considerable work has already been done in other parts of the world, such as India, to grade different types of sorghum according to how drought-tolerant or drought-susceptible they are.
‘My work is to take (these graded plants) and investigate the proteins that are expressed in them. If I can see a protein standing out in one variety then it can give us a clue that that’s what makes one variety drought-tolerant. And maybe the absence of that particular protein in another variety which makes it weaker under drought stress.’

Most of this work takes place in a laboratory using high-tech equipment to scrutinise the plant’s molecular make-up. But they can also look at the physiology of the plant – at its leaf size or root structure, for instance – and collate physical traits with the protein information Ndimba’s team gets in the laboratory.

‘If a protein is known to be involved in a certain pathway, for instance root extension, then it might explain how the plant has better water absorbing qualities. Or a specific protein might explain why some plants’ leaves have a better mechanism of avoiding water loss than others.’

Their work seeks to unlock the secrets of these plants and how some of them are able to survive extreme conditions, while others aren’t. This information can then be used to assist sorghum breeders as they cultivate different and possibly more appropriate sorghum hybrids.

‘You could breed those proteins into weaker sorghum varieties using classic breeding techniques,’ he explains. For instance, a drought-tolerant type of sorghum may not produce good grain, but its proteins can be bred into a strain that may be ‘weaker’ but produce good grain. However, redesigning plants at a genetic level wouldn’t happen yet since transgenic work on sorghum isn’t allowed under current laws in South Africa.

Prof Ndimba and his team have identified several proteins which they believe are responsive to dehydration stress in the plant. The next step is to take the laboratory experiments into the field to see if these naturally drought-tolerant plants respond in the same way.

In 2011, Ndimba was also appointed as a specialist researcher with the Agricultural Research Council (ARC), a position which has given his team access to farmlands near East London in the Eastern Cape. Field trials are set to begin, which will help the researchers home in on which of the proteins are at work in the sorghum species they’re studying, either contributing to or undermining their level of drought tolerance. 

Ndimba’s work has attracted some attention in the past three years, drawing in research grant money valued at over R7.5 million from various sources, including the National Research Foundation (NRF), the ARC, UWC and others.

Part of this funding included an NRF national equipment programme grant which allowed the ARC and UWC to buy in a new high-end multi-purpose mass spectrometer, something which has opened the entire university and ARC to greater agriculture-related research. This has allowed Ndimba’s team to establish itself as a national specialist in the field of proteomics in agriculture, an area formerly seen as relatively ‘low-tech’.

‘The original mass spectrometer we had here was the equivalent of an old Beetle, but this new one is a Porche,’ laughs Ndimba, explaining how it allows for opportunities for the university and the ARC researchers beyond just his unit, giving them access to high-tech equipment that is usually the domain of medical biosciences.

All these developments will culminate in the ARC and UWC biotechnology department launching the National Agricultural Proteomics Research and Services Unit (NAPRSU) this May – the first of its kind in the country.

The work being done by ARC/UWC’s proteomics unit can also be used to help develop more drought resistant types of maize, wheat, barley and rice, since the same kinds of proteins are at work in those crops, too. But sorghum is seen as an ‘orphan’ crop in southern Africa. Few people in this region still grow it and indigenous knowledge associated with the plant is lost as people move to cities and abandon subsistence agriculture.

However, Ndimba says it is naturally more drought tolerant than maize, wheat, rice and barley, and gives good yields without needing inputs such as water and fertiliser. It can be grown as a cereal crop in the interests of food security, but also as fodder for farm animals and can even be a source of organic matter for biofuels. He calls it his ‘three f’s’: food, feed and fuels.
‘Gram for gram, some varieties of sorghum produce as much sugar as sugar cane, but it grows three times faster and is much more water efficient. This sugar can be fermented into bioethanol. India is already doing this.’

The unit’s first commercial bioethanol venture started up in Fort Cox recently, near the university town of Alice in the Eastern Cape, where 3 ha of sweet sorghum is under cultivation in anticipation of being turned into a liquid fuel for vehicles. The first crop was planted in January, the processing-to-bottling equipment has been installed and the first harvest is expected this May.

The main limitation, explains Ndimba, is capacity on the farm. And there’s the question of keeping livestock out of the fields. But by the end of the three year project, they expect to bring in 30 ha of sorghum for conversion to bioethanol.

Since Ndimba demonstrated the lab experiments with the sorghum in 2010, he has added a fourth ‘f’ to the project’s focal areas: that of fibre.

The proteomics team is now working with Ohio State University to investigate the possibility of mixing the biomass of certain crops that have a natural adhesive quality, with sorghum discards, to make building materials and construction boards. By combining the mash-like discards of latex-producing crops with the ground up waste of processed sorghum stems, they are looking at ways to make fibrous materials.

‘It is highly innovative and has a lot of potential uses. It’s aimed towards an agricultural practice that has zero waste. The “de-juices” stems from sorghum can be used for many purposes, one for feed, another as a mash and also to put back into field as fertilizer. Now, mix with another material, it can make fibre too.’

Ndimba peruses the young grass tufts. One of his next missions is to see if sorghum can be grown commercially in the winter rainfall region of the Cape. But in the meantime plant breeders at the Agricultural Research Council are keen to use his findings to help them design the most hardy sorghum plants possible.

West Cape News