Rhizo-Rice: a novel ideotype for deeper roots and improved drought tolerance

Rice is a mainstay of global food security. Drought stress is a primary limitation to rice yields and is projected to worsen in the future due to the effects of global climate change. The development of rice cultivars with better drought tolerance is therefore an important strategic goal for global food security.

This project addresses this need by developing Rhizo-rice, new rice lines that have root traits that permit them to have both improved soil exploration and more efficient water capture under drought conditions. Rhizo-rice lines will have 1) steeper root growth angles, 2) fewer major roots, 3) greater root branching in deep soil, 4) increased formation of root air spaces (aerenchyma), which reduces the cost of root tissue, and 5) smaller water conductance vessels (xylem), which forces the plant to use soil water more sparingly. It is hypothesized that these traits will have much more value in combination than would be predicted from their isolated effects. This project will evaluate the benefits of Rhizo-rice lines in the field and computer simulation modelling and will discover genetic elements controlling Rhizo-rice root traits. Furthermore, we will evaluate these root traits in rice breeding lines in use in Thailand and will train Thai scientists in methods to incorporate root traits in rice breeding programs.

This project integrates leading rice researchers and breeders in Thailand, leading crop physiologists in the UK and at the International Rice Research Institute in the Philippines, and leading root modelers in the UK. We will investigate how different root architectures and drought conditions affect rice growth by measuring features of the root system in rice plants grown in different conditions. By recording the number, length and angle of different types of roots and taking microscopy images of the root structures, we will test how these features affect drought tolerance. These measurements will be complemented by computational modelling, which will enable us to test many different root structures and drought conditions. We have previously developed computational models to simulate root growth in maize, barley, common bean, lupin and squash. We will adapt these models to simulate rice root growth, which will enable us to predict the best type of root growth to maximise water uptake in drought conditions. Finally, we will determine which genes are responsible for creating the desirable root structures. We will use recently developed techniques to analyse the genes and root structures in many different varieties of rice, which will enable us to identify suitable varieties for maximising drought tolerance. This project will generate several tools to facilitate the breeding of more drought tolerant rice lines. It will validate specific root traits as selection targets in rice breeding; will discover genetic markers for these traits; will identify sources for desirable root traits in rice germplasm, and will enhance the ability of Thai scientists to create a team for breeding rice lines with superior root traits.

This project addresses drought tolerance in rice, which is a primary constraint to the production of a leading global crop. It therefore addresses a problem of surpassing significance for global food security and economic development in many poor nations. This project is also significant in testing novel hypotheses regarding root traits that improve drought tolerance in rice. These concepts are directly relevant to other tillering cereal crops including wheat, barley, rye, and oats, and more generally all cereal crops including maize, sorghum, and millet. Collectively these crops sustain most of humanity. Drought is the most important global limitation to food production, and is projected to worsen in the future due to global climate change. By contributing to the development of more drought tolerant crops, this project addresses a surpassing challenge for human welfare.

Key project impacts will include:

1) This project will have direct benefits for rice breeding in Thailand. The ideotypes, selection protocols, genetic markers, parental lines, and trained Thai researchers developed in this project will directly benefit rice breeding programs in Thailand, because our project team includes leading members of Thai rice research and breeding programs. Ongoing drought breeding programs for rice are directly engaged in the project and will employ these tools and advances as soon as they are developed.

2) By exploring the root adaptations of the uniquely diverse Thai rice germplasm, this project is likely to discover parents and markers that have importance to the global rice community.

3) Our project team includes the leading drought physiologist at the International Rice Research Institute (IRRI), so our discoveries will directly benefit the world's leading international rice research organization, with breeding programs and outreach throughout the global rice community. IRRI germplasm is shared openly throughout the world and is especially important in developing nations of Asia. The link with IRRI will facilitate the inclusion of outputs from this project into IRRI's Multi-Environment Testing (MET; 6 countries in Southeast Asia) and the International Network for Genetic Evaluation of Rice (INGER: 30 countries across Asia) systems for evaluation of promising germplasm, as well as the stress-tolerance rice evaluation networks (such as STRASA) in Africa and South Asia. This will enable our project to extend impact to huge numbers of beneficiaries.

4) By testing novel hypotheses about drought adaptation in cereal crops, this project will make basic contributions to our scientific understanding of root biology, environmental stress biology, and plant-soil interactions. Although these concepts were developed to address the practical challenge of growing food crops under drought, they are fundamentally new concepts that advance our understanding of plant biology.

5) This project will develop SimRoot/rice, a powerful new discovery platform for rice research. SimRoot has been a unique research tool that has been instrumental in understanding the acquisition of soil resources by root systems of maize, common bean, and squash. SimRoot/rice will be a powerful research tool for the rice research community for diverse problems including drought adaptation but also nutrient acquisition, yield optimization, and rice responses to global climate change. We will actively engage with researchers in industry to ensure the tools developed are fully exploited.

6) This project will educate thousands of people in root biology methods via web outreach. Our existing root biology web site serving root biologists and crop breeders reaches over 50,000 users annually in three languages (English, Spanish, and Portuguese). This project will add rice as a focus and Thai language versions of these materials, which will support the global rice community and specifically the rice community in Thailand.