Genetic Control of Nodal Root Angle and its Effects on Root Distribution and Drought Adaptation in Sorghum

Abstract

Genetic improvement of drought resistance in sorghum is essential to enhance production under water limiting environments. Recent research has demonstrated that in sorghum, the angle of the first flush of nodal roots is a key determinant of spatial patterns of water acquisition in mature plants and critical to drought adaptation. Here we summarise studies on the genetic control of nodal root angle in sorghum seedlings and its effects on root distribution and water extraction of mature plants. Phenotyping for nodal root angle in small soil filled chambers have indicated extensive genetic variation (15°-50°) with high heritability. Further phenotyping and genotyping of a mapping population identified four QTLs for nodal root angle, which explained 58.2% of phenotypic variance. These QTLs co-located with QTLs for stay green and were correlated with grain yield from breeding trials. A high-throughput phenotyping platform has been developed to phenotype multiple complementary populations and genotyping has identified common genomic regions associated with nodal root angle. Selected lines with contrasting root angle were grown in large soil filled chambers to assess differences in root distribution patterns and water extraction patterns of mature plants. Lines with narrow root angle had more vertical root distribution, greater root elongation rate, and greater occupancy of roots and water extraction at depth. They also showed advanced head emergence and flowering with greater panicle weight before the onset of severe drought in drying soils. This study suggests that nodal root angle presents an opportunity to improve drought adaption in sorghum via molecular breeding. It is anticipated that the identification of genetic regions controlling nodal root angle will support molecular breeding for drought adaptation by manipulation of root traits for which selection has been previously difficult.