Aus rice root architecture variation contributing to grain yield under drought suggests a key role of nodal root diameter class

Abstract

The aus rice variety group originated in stress‐prone regions and is a promising
source for the development of new stress‐tolerant rice cultivars. In this study, an aus
panel (~220 genotypes) was evaluated in field trials under well‐watered and drought
conditions and in the greenhouse (basket, herbicide and lysimeter studies) to investigate
relationships between grain yield and root architecture, and to identify
component root traits behind the composite trait of deep root growth. In the field
trials, high and stable grain yield was positively related to high and stable deep root
growth (r = 0.16), which may indicate response to within‐season soil moisture fluctuations
(i.e., plasticity). When dissecting component traits related to deep root
growth (including angle, elongation and branching), the number of nodal roots
classified as 'large‐diameter' was positively related to deep root growth (r = 0.24),
and showed the highest number of colocated genome‐wide association study
(GWAS) peaks with grain yield under drought. The role of large‐diameter nodal roots
in deep root growth may be related to their branching potential. Two candidate loci
that colocated for yield and root traits were identified that showed distinct haplotype
distributions between contrasting yield/stability groups and could be good
candidates to contribute to rice improvement.