Genetic diversity in Ethiopian sorghum germplasm for root system architecture and trait association

Sorghum productivity in arid and semi-arid regions of Africa is very low, mainly due to limited water availability. Roots are the primary conduit for plants to access moisture and nutrients. Root growth angle determines the direction of root elongation in the soil profile and is an important trait for adaptation to water-limited environments. Information on the extent of genetic variation in RSA and its relationship with drought response is critical for improving the performance of the crop under drought stress. The objective of this study was to examine the degree of genetic variability for root and shoot traits in sorghum germplasm during the seedling stage. Two hundred and ninety-one sorghum germplasm adapted to different agroecologies of Ethiopia were phenotyped for root and shoot traits using a purpose-built root chamber in the greenhouse at Jimma University. The experiment was set up in a row-column design with three replicates. Significant genetic variation (P < 0.01) was observed for all traits examined except root hair number and shoot dry weight. Root angle varied from 9° to 21.3° with an average of 14.9° and showed moderate heritability of 44.38%. Root dry weight also exhibited moderate heritability (49.3%). Correlation and path coefficient analysis revealed that root angle (RA) was uncorrelated with other RSA traits. Cluster analysis using the RSA traits grouped the 291 genotypes into four different clusters. The first three principal components accounted for about 50% of the total variation. The results demonstrate that the Ethiopian sorghum germplasm exhibits large variation in RSA traits that can be harnessed in breeding programs to enhance sorghum productivity under drought stress.