Rice Straw Project

Hundreds of millions of tons of rice straw and husks are burned in the field every year simply to get rid of them. This combustion causes very bad air quality through the release of black carbon particles, methane (and larger volatile compounds), carbon monoxide and the generation of ozone. Between them, these emissions cause respiratory illness and premature death in exposed populations, significant losses in crop yield due to the toxic effects of ozone and shading by black carbon, and increased global warming, especially due to methane and black carbon. All of these negative impacts are avoidable if alternative uses for rice straw can be found. Rice straw currently finds little application as animal feed because of its poor quality. Rice straw is composed of roughly 75% polysaccharides and this can provide considerable value as animal feed, unfortunately, this straw is currently hard to digest, partly due to its content of lignin, and more importantly because rice straw has a high content of silica. Silica can make up to 10% of the dry weight of rice straw and this not only make it hard to digest but also highly unpalatable. Our overall aim for this project is to find ways to improve the quality of rice straw as animal feed in order to move it from being burned to becoming a valuable resource for the production of meat and dairy products.

We have been studying rice straw as a potential feedstock for producing biofuels by fermentation of its component polysaccharides. As in uses of rice straw for animal feed, this process is also challenged by straw digestibility and we have been using genome-wide association studies (GWAS) to identify genes that are involved in making straw hard to digest and molecular markers that can be used in breeding studies to improve this characteristic. For this work we have made detailed genetic maps for a collection of 170 diverse rice accessions collected and grown in Vietnam. We have measured how well the straw from these varieties is digested by commercial digestive enzymes (cellulases) and also measured their content of silica and lignin. This revealed that some varieties are more than four times more digestible than others and that silica content in some more digestible varieties are lower than 1%. In the work proposed here, we wish to expand these studies to examine the characteristics of straw from the rice diversity panel in terms of animal feed quality. This will be done in a high-throughput manner in the laboratory in the UK in order to allow us to carry out GWAS to identify markers to help in breeding for improved straw in commercial varieties and to help us identify new genes that affect these characteristics. On a science level, we will focus on increasing our understanding of how silica affects straw digestibility, by looking for cell wall-related genes that affect silica content.

From a point of view of seeing our studies have real impacts on straw use, we will work with scientists in Vietnam and the Philippines to demonstrate the potential value of straw improvement. We will do this by identifying a subset of rice varieties with contrasting animal feed value (high and low) and using these in feeding trials using carabao. Carabao are water buffalo traditionally used as draft animals in South East Asia that are being developed for meat and dairy production in tropical countries. The results of these trials will demonstrate the benefits of using higher quality straw for animal feed and we will use this information to educate farmers of the benefits of growing dual purpose rice varieties for grain and animal feed production, and rice breeders of the benefits of improving straw value in commercial varieties. In the long term our work has the potential to improve the environment and well-being of people in rice growing countries as well as increasing farmer income and the availability of high protein products for local consumption.

Developing rice resources for resilience to climate change and mitigation of carbon emissions