Characterization of Ethiopian sorghum [Sorghum bicolor (L) Moench] germplasm collection for drought adaptation traits associated with roots

Drought is the most important abiotic stress affecting crop production in Ethiopia, leading to huge crop failures. Despite its inherent drought tolerance, moisture stress is nonetheless one of the major constraints for sorghum production. The root system architecture (RSA) of plants influences adaptation to water-limited conditions and determines the capacity of a plant to access soil water. Hence, better understanding the genetic variation of RSA could improve sorghum for water-limited areas. The objective of this study was to explore the extent of genetic variation in RSA in a diverse range of sorghum germplasm, including about 1000 sorghum landraces collected from sorghum-growing regions of Ethiopia, together with another 1000 Ethiopian breeding lines and varieties. The experiment was conducted in a greenhouse using 10 purpose-built root chambers (50 cm high, 45 cm wide and 3mm thick) in a row and column design, with four replications using red soil. Four seeds were sown in one side of the Perspex and thin out to one when the seeds fully emerged. Data on first flush nodal root angle (relative to vertical) were recorded when plants reached the six leaf stage and the first flush of nodal roots was visible. The root system that was visible through the clear perspex was photographed on both sides of each chamber using digital cameras. The images were used to measure the angle of each of the first pair of nodal roots at two cm distance from the base of the stem, using software. Significant genetic variation for nodal root angle was found among the genotypes ranging from 13.5° to 30.4° with a moderate to high heritability of 58.8-84.9%. However, nodal root angle was not significantly correlated with other traits, implying that these mechanisms could potentially operate independently. Variation in nodal root angle could be used by sorghum breeders to improve drought adaptation