Image: Dr Byrt with some of the diverse range of sorghum types studied in the glasshouse.
Image credit: Haiyen Nguyen.

Biofuels are increasingly becoming an important supplement and replacement for diesel and petrol, which, as fuel for transport, produce 14 per cent of the world’s greenhouse gas emissions[1]. Two big advantages of biofuels are: they are a renewable resource that does not require mining fossil fuels; and they deliver a roughly neutral net carbon dioxide impact on the atmosphere, due to the recapture of carbon from the atmosphere that occurs as a natural part of the growth of the crop.

One concern with using biofuels for transport is the diversion of resources from food production. However, researchers working at the Australian Research Council Centre of Excellence in Plant Cell Walls, at The University of Adelaide, have recently discovered that the stems of a wild variety of the common sorghum plant have properties that make it a suitable contender for biofuel production.  

Sorghum is already widely grown in New South Wales and Queensland as a feed and forage crop for animals, and the grain is becoming increasingly popular for human consumption as a gluten-free alternative to other cereal grains. In 2015, for the first time, it was Queensland’s most valuable cereal crop with a production that was estimated to be worth $432 million[2].

“The part of the sorghum plant we studied as a potential raw material for making biofuel is the stem. If stems are used for biofuel production, the grain can still be used for cattle feed, and leaves for mulch,” says Dr Caitlin Byrt, whose research into the biofuel potential of sorghum stems has recently been published in Plos One. “Sorghum stem is ideal for making biofuel, relative to using wheat or corn, because we don’t eat sorghum stems and they can be produced in low input systems.”

Dr Byrt is currently funded by the ARC, through a Discovery Early Career Research Award (DECRA), to undertake research to identify the mechanisms that control key processes in plant cell walls and cell membranes. These processes influence the productivity of economically-important grain crops and understanding their function is of great interest to plant industries.

“We identified that a wild native variety of sorghum which grows on the side of the road and in people’s backyards has a large amount of an ideal type of carbohydrate in its stem, which can be used for making biofuel. By breeding this variety with commercial cultivars, it should be possible for us to introduce these desirable qualities into what is currently a part of the plant with little economic value.”

This particular kind of carbohydrate, called (1;3;1,4)-β-glucan, has advantages over sucrose-rich materials as a source of carbon for biofuel production as it’s less prone to degrading after harvest, so can be stored more easily and processed at some distance from the site of harvest. It also has advantages over other kinds of raw materials that are high in cellulose, because it is easier to convert (1;3;1,4)-β-glucan to fermentable sugar.

“One thing that is exciting about this paper,” says Dr Byrt, “is that if you use Google to look for the most commonly considered materials used to make bioethanol, you find a big focus on cellulosic bioethanol. But it is relatively expensive to make bioethanol from cellulose because you need to use costly enzymes to release the glucose. Glucose can be more easily and cheaply released from (1;3;1,4)-β-glucan relative to cellulose.”