Abstract
Simple SummarySorghum is a climate-resilient crop grown in limited rainfall areas globally. However, climate change has increased temperature and shortened rainfall durations, which has constrained crop yield. We reviewed mechanisms of drought tolerance and application of marker-assisted selection in sorghum. Marker-assisted selection uses DNA molecular markers to map quantitative trait loci (QTL) associated with stay-green. Stg1, Stg2, Stg3, Stg4, Stg3A, and Stg3B QTLs associated with stay-green and high yield, have been mapped in sorghum. These QTLs are used for introgression into the senescent sorghum varieties through marker-assisted backcrossing.Sorghum is an important staple food crop in drought prone areas of Sub-Saharan Africa, which is characterized by erratic rainfall with poor distribution. Sorghum is a drought-tolerant crop by nature with reasonable yield compared to other cereal crops, but such abiotic stress adversely affects the productivity. Some sorghum varieties maintain green functional leaves under post-anthesis drought stress referred to as stay-green, which makes it an important crop for food and nutritional security. Notwithstanding, it is difficult to maintain consistency of tolerance over time due to climate change, which is caused by human activities. Drought in sorghum is addressed by several approaches, for instance, breeding drought-tolerant sorghum using conventional and molecular technologies. The challenge with conventional methods is that they depend on phenotyping stay-green, which is complex in sorghum, as it is constituted by multiple genes and environmental effects. Marker assisted selection, which involves the use of DNA molecular markers to map QTL associated with stay-green, has been useful to supplement stay-green improvement in sorghum. It involves QTL mapping associated with the stay-green trait for introgression into the senescent sorghum varieties through marker-assisted backcrossing by comparing with phenotypic field data. Therefore, this review discusses mechanisms of drought tolerance in sorghum focusing on physiological, morphological, and biochemical traits. In addition, the review discusses the application of marker-assisted selection techniques, including marker-assisted backcrossing, QTL mapping, and QTL pyramiding for addressing post-flowering drought in sorghum.
Highlights
A drought is a condition when soil moisture fails to support plant growth due to low normal precipitation
Impact of climate change projects that the yield will decrease by 19–20% on cereal crops except sorghum and millets, for which yield will decrease less than other cereals from 2040–2069
It needs different selection tools for screening drought tolerance lines that cope with drought stress
Summary
A drought is a condition when soil moisture fails to support plant growth due to low normal precipitation. Multi-approach strategies to understand the mechanism of the crop tolerance are paramount to exploit traits that are important for further improvement to address drought, which is projected to increase because of climate change [12]. The breeding of sorghum varieties for drought tolerance, disease resistance, and improved yield increases the production and the productivity per unit area This is achieved by application of conventional and molecular breeding and biotechnology tools to shorten the breeding cycles [20]. Drought affects sorghum plants differently at physiological growth stages, for instance, seedling, pre-flowering, and post-flowering stages, which contribute to the final yield. Water stress at post-flowering growth stage causes yield losses of 87–100% since at this stage, plants need plenty of water for grain filling [28]. Water stress at post-flowering growth stage causes yield losses of o8f71–8100% since at this stage, plants need plenty of water for grain filling [28]. Drought after flowering has a negative effect on the filling of mocreprheaollso, sgoiciat lcapulsaensta gsirgonwifitchan[c3e4l]o. sHs oofwcreovpesrb, epcalaunsetsathtahvisesttahgee,apblailnittsyatbosorluesteulymneeendormal groawntahdreeqgueanteerwaatetesracfotenrteantpienritohde osofidl [r3o5u].ghInt. aDdrdoituiognh,tpalfatnetrsfhloawveerthinegabhialistya tnoecgoapteive effecwt oitnh dthroeufgilhlitnsgtreosfs,cienrceluadlsi,nsgopihtycsaioulsoegsical,smigonripfihcoalnocgeicalol,sasnodfbciroochpesmbieccaal museechaatntihsmisss. tage, plaPnhtsysaibolsoogliuctaellmy enceheadniasmn aindveoqluveastethwe aatdejrusctomnetnent itninphthoteosyonilth[3e5si]s.,Icnhlaodrodpithiyolnl ,cponlatenntst, have thestaobmilaittyal tcooncdoupcetawncieth, adnrdoturagnhstpsirtarteisosn, riantcel.uTdhiengplapnhtys srieodluocgeicleaal,f wmaotrepr hpooltoengtiicaalla,nadnd biochreemguilcaatel mosemchotainc ipsmotesn. tPiahlywsihoilloegkiceaepl imngechhigahnicshmloirnovpohlyvllescotnhteenatdfjourstpmhoetnotsyinntphhesoitsosynthetsoiss,ucphploorrtopplhaynltlgcroonwttehn.tU, ssteofuml amtaolrpcohnoldougcictaalnfceea,tuarneds itnrcalnusdpeiraadteiqounarteatpel.aTnthheepiglahnt,ts reducroeoltesadf ewvealtoeprmpeontet,nbtiioaml aanssdprreogduulcattieono,samndotliecapf oartreanntgiaelmwenhtilteokaelleopwinpglahnitgshtocahdloarpotphyll during water scarcity, while a biochemical mechanism involves vital processes taking conptleancet ifnorplpanhtostdousyrinntghdersoisugthot.sTuhpepreofrotrep,lpahnytsgiorloowgitchal., Umsoerfpuhlolmogoircpalh, oanlodgbicioaclhfeematicuarles inclumdeecahdaneqisumasteplpaylatnhte hmeaijgohr tr,orleoointscodpeivngelwopitmh denrotu, gbhiot mstraessss ipnrsoodrguhcutimon, a, sadnedsclreiabfedarinrangedetails below
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