Sorghum in dryland: morphological, physiological, and molecular responses of sorghum under drought stress

Abstract

Droughts negatively affect sorghum's productivity and nutritional quality. Across its diversity centers, however, there exist resilient genotypes that function differently under drought stress at various levels, including molecular and physiological. Sorghum is an economically important and a staple food crop for over half a billion people in developing countries, mostly in arid and semi-arid regions where drought stress is a major limiting factor. Although sorghum is generally considered tolerant, drought stress still significantly hampers its productivity and nutritional quality across its major cultivation areas. Hence, understanding both the effects of the stress and plant response is indispensable for improving drought tolerance of the crop. This review aimed at enhancing our understanding and provide more insights on drought tolerance in sorghum as a contribution to the development of climate resilient sorghum cultivars. We summarized findings on the effects of drought on the growth and development of sorghum including osmotic potential that impedes germination process and embryonic structures, photosynthetic rates, and imbalance in source-sink relations that in turn affect seed filling often manifested in the form of substantial reduction in grain yield and quality. Mechanisms of sorghum response to drought-stress involving morphological, physiological, and molecular alterations are presented. We highlighted the current understanding about the genetic basis of drought tolerance in sorghum, which is important for maximizing utilization of its germplasm for development of improved cultivars. Furthermore, we discussed interactions of drought with other abiotic stresses and biotic factors, which may increase the vulnerability of the crop or enhance its tolerance to drought stress. Based on the research reviewed in this article, it appears possible to develop locally adapted cultivars of sorghum that are drought tolerant and nutrient rich using modern plant breeding techniques.

Keywords: Drought tolerance; Germplasm; Grain quality; Sorghum; Source-sink relations.

Fig. 1

PCA-biplot of sorghum genotypes grown a at two locations in Botswana in 2015 (Motlhaodi et al. 2018) and b at two locations in South Africa in 2011 (Ng’uni et al. 2016). The two studies used different sorghum genotypes

Fig. 2

Diagrammatic depiction of morphological, physiological, biochemical, and molecular responses of sorghum to drought stress. This figure was created with BioRender (https://biorender.com/)