Physiological mechanisms of drought tolerance in sorghum, genetic basis and breeding methods: A review

Abstract

Sorghum is grown in semi-arid to arid regions of the world and serves as the staple food for about half a billion people in sub-Saharan Africa and Asia. The adaptation of grain sorghum to a wide range of environmental conditions has led to the evolution and existence of extensive genetic variation for drought tolerance. Consequently, sorghum is expected to play an increasingly important role in agriculture and meeting world food demand in the face of climate change, land degradation and increasing water scarcity. Drought is a complex phenomenon, and is considered one of the most significant factors limiting crop yields around the world and continues to be a challenge to plant breeders, despite many decades of research. Underestimating the genetics and the physiological mechanisms underlying drought tolerance is vital for the breeding to alleviate adverse effects of drought in order to boost productivity. In this literature review, research findings from the 1970s up to present are included. Most of the basic researches on the mechanism of drought tolerance were done in the early 1980s, and most of the current researches focus on verification and fine-tuning of methodologies. The paper outlines the main effects of drought on crop growth and development, and yield. It then examines the basic information on physiological mechanisms of drought in crops. Subsequent discussion is given on the genetic control of drought tolerance, and breeding methods in sorghum.

Grain Sorghum Response to Water Supply and Environment

“…With the combination of root structure and stomata opening, sorghum is able to manage water stress better than corn . Sorghum will roll its leaves to decrease radiation intensity although it is believed that more drought tolerant lines have less leaf rolling and lower stomatal conductance (Beyene et al, 2015). Sorghum's ability to produce solutes for osmotic adjustment contributes to its greater drought tolerance .…”

“…Sorghum varieties that stay green longer into reproductive stages are shown to have better N utilization (Borrell et al, 2000), better drought tolerance, reduced lodging, and greater resistance to stalk rots (Beyene et al, 2015). Stay green in sorghum is a result from having more N in the leaves during grain filling compared to senescent sorghum (Borrell et al, 2001).…”

“…Within sorghum, there are some root traits that make certain lines or varieties more drought tolerant than others. Characteristics such as root length, density, mass, volume, and thickness are highly correlated with drought avoidance (Beyene et al, 2015). Root architecture is also a valuable trait to look at for drought avoidance, because a narrower root angle allows for deeper root penetration and a faster elongation rate (Singh et al, 2010).…”

“…Drought occurring before flowering reduces seed number by reducing plant stands, tillering, number of heads, and/or seeds per head; but drought after flowering reduces seed size by reducing transpiration efficiency, CO2 fixation, and carbohydrate translocation (Beyene et al, 2015). Emendack et al (2014) postulated that high grain HI is a good predictor for pre-flowering drought tolerance and grain yield.…”

“…Drought stress limits crop yields most severely in semi-arid regions of the world (Afshar et al, 2014) and can cause other problems like disease . Drought tolerance is a complex process that involves morphological, physiological, and biochemical processes (Beyene et al, 2015).…”