Using root-soil interactions in the rhizosphere as valuable traits for selection against drought
Résumé
The rhizosphere, meaning the soil volume influenced by the living roots, hosts several important ecological processes implicating the soil, the root system and active microbiota. These various interactions often impact soil carbon (C) content and nutrient dynamics, as well as soil water retention, by modifying its biological and physico-chemical properties. Well-known root adaptive traits for drought tolerance include deep rooting and increased root development, both of which ensure better exploration of the soil volume required for greater water uptake. However, the intensity of root-soil-microbiota interactions shape the size of the rhizosheath (i.e., the soil mass that remains attached to roots after plant excavation), which could modulate the water retention capacity of soil. Indeed, genotypes with larger rhizosheath respond better to drought stress than those with a smaller rhizosheath in several plant species. From a breeding perspective, intra-specific variation in rhizosheath size has recently been demonstrated in two important crops in West Africa: pearl millet and maize. Therefore, genotypes with large rhizosheath could be considered for varietal selection for adaptation to drought. Ongoing genome wide association studies (GWAS) should confirm genetic control of rhizosheath size and map candidate genes and investigations should be performed on the mechanisms that support this genetically complex trait.