Understanding the genetic control and physiological traits associated with rhizosheath production by barley (Hordeum vulgare).

There is an urgent need for simple rapid screens of root traits that improve the acquisition of nutrients and water. Temperate cereals produce rhizosheaths of variable weight, a trait first noted on desert species sampled by Tansley over 100 yr ago. This trait is almost certainly important in tolerance to abiotic stress. Here, we screened association genetics populations of barley for rhizosheath weight and derived quantitative trait loci (QTLs) and candidate genes. We assessed whether rhizosheath weight was correlated with plant performance and phosphate uptake under combined drought and phosphorus deficiency. Rhizosheath weight was investigated in relation to root hair length, and under both laboratory and field conditions. Our data demonstrated that rhizosheath weight was correlated with phosphate uptake under dry conditions and that the differences in rhizosheath weight between genotypes were maintained in the field. Rhizosheath weight also varied significantly within barley populations, was correlated with root hair length and was associated with a genetic locus (QTL) on chromosome 2H. Putative candidate genes were identified. Rhizosheath weight is easy and rapid to measure, and is associated with relatively high heritability. The breeding of cereal genotypes for beneficial rhizosheath characteristics is achievable and could contribute to agricultural sustainability in nutrient- and water-stressed environments.
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