Abstract
Sorghum is particularly drought tolerant compared with other cereal crops and is favoured for subsistence farming in water scarce regions of the world. This study was conducted to identify South African sorghum landraces with superior drought tolerance compared with a drought-tolerant breeding line (P898012). Seedlings of 14 South African sorghum landrace accessions were initially screened for drought tolerance by assessing percentage leaf water content (LWC) during progressive water deficit. Four landraces (designated LR5, LR6, LR35, and LR36) recorded higher LWC than P898012. These were subsequently evaluated with P898012 during the reproductive growth stage, for their physiological responses to mild (4days) and severe (6days) water stress treatments and a moderate re-watered treatment on day 7. Plant height, soil moisture, and LWC were measured during harvests. Chlorophyll, carotenoid, and proline contents were quantified. All five genotypes maintained LWC above 80% during mild and severe stress treatments. For LR35 and LR36, LWC were recorded within 8% less in comparison to their well-watered controls following the moderate re-watered treatment. Significantly higher chlorophyll and carotenoid contents were recorded for both LR6 and LR35 in comparison to P898012 during severe stress. When LWC was reduced in LR36 (to 73.68%) and LR35 (to 73.51%), their proline content significantly increased by 14- and 16-fold, respectively. In this study, we have identified four previously uncharacterised sorghum genotypes exhibiting drought tolerance and described their physiological responses during water deficit and moderate re-watering. Aside from their application to breeding, these landraces are valuable resources to elucidate genetic mechanisms that enable drought tolerance in South African sorghum.
Highlights
Drought is a complex environmental stress and major constraint to crop productivity
Two independent water stress investigations were conducted to: (1) screen 14 South African, sorghum landrace accessions for drought tolerance during the vegetative, seedling stage together with drought susceptible ICSV112 and drought tolerant P898012 breeding lines and (2) assess the physiological responses of landraces selected from the water stressed seedling screen, during the drought sensitive, reproductive growth stage (GS) II of sorghum development at eight weeks after emergence
During the moderate re-watered treatment after seven days of water deficit, P898012, LR5 and LR6 significantly maintained leaf water content (LWC) compared with their controls; whilst LWC recorded for LR35 and LR36 were less than 8% lower in comparison to their controls
Summary
Drought is a complex environmental stress and major constraint to crop productivity (reviewed by Mishra and Singh, 2010; Farooq et al, 2012). Sorghum, which is indigenous to Africa, is a close relative of sugarcane and cereals such as maize and pearl millet It is a versatile crop and the utilization of the whole plant is far-reaching; sorghum is grown for food, animal feed, fibre, fuel and used for some industrial purposes (Wall and Ross, 1970; House, 1985; Paterson et al, 2009). The early vegetative stage and reproductive stages (pre- and post-flowering) of sorghum are vulnerable to the effects of water deficit (Tuinstra et al, 1997; Kebede et al, 2001; Wani et al, 2012). Water stress during pre- and post-flowering stages impacts grain development and yield of the crop (McKersie and Leshem, 1994). The ability to withstand water deficit at these stages is critical to productivity
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