Agro-morphological diversity of Ethiopian sorghum [Sorghum bicolor (L.) Moench] landraces under water limited environments

Drought stress is one of the major constraints affecting sorghum [Sorghum bicolor (L.) Moench] production in rain-fed regions of the Semi-Arid Tropics. Ethiopia is the suspected center of origin for sorghum and as such has tremendous variability for a wide range of traits. Ironically, there has been little systematic characterization of Ethiopian sorghum for traits of agronomic interest including drought tolerance. Hence, the objectives of this study were to evaluate the phenotypic diversity of 315 sorghum accessions (314 landraces plus 1 standard check) collected from farmers’ fields of diverse geographic regions in Ethiopia, and to identify potential sources of drought tolerance for future breeding programs. We phenotyped these accessions for ten agro-morphological traits at two water limited environments (Kobo and Mieso). Significant (p < 0.05) differences among genotypes and genotype by environment interaction effects were found for all traits studied, as well as significant correlations between agro-morphological traits of primary interest in sorghum improvement programs. While a lack of geographic differentiation suggested extensive gene flow among the regions, agro-morphological traits reveal clear differentiation among eight clusters that are phenotypically distinct. An intriguing hypothesis is that the richness of diversity in Ethiopia may facilitate selection for different allele combinations that result in particular suites of traits (ideotypes). This would provide great opportunity to identify diverse sources of tolerance and/or highly contrasting lines that could be used for sorghum improvement programs, crossing to potentially obtain even more extreme, transgressive, phenotypes. High yielding and drought tolerant lines were more abundant among accessions from lowland areas, implying that targeted collection from these areas would be important for improving drought adaptation of sorghum. Overall, high phenotypic trait-based variability for sorghum improvement remains available in Ethiopia, with further collection and/or detailed characterization using molecular markers needed to promote the conservation and effective use of these resources.