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.