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Pre-breeding of sorghum [sorghum bicolor (L.) moench] for drought tolerance in the semi-arid zones of Nigeria=Ukulungisela ukuzalanisa kweSorghum [Sorghum bicolor (L.) Moench] Yokubekezelela Isomiso Ezindaweni Ezomile ZaseNigeria.

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Sorghum [Sorghum bicolor (L.) Moench] is a staple food crop serving millions of people in Africa and Asia's arid and semi-arid agro-ecologies. Sorghum is widely cultivated in Northern Nigeria, serving diverse value chains, including the food and feed sectors and the brewery industry. However, the potential production and productivity of sorghum in Africa, including Northern Nigeria, is constrained by severe drought stress associated with climate change. Furthermore, smallholder farmers in Nigeria still cultivate low-yielding and drought-susceptible unimproved sorghum landraces. Developing drought-tolerant sorghum cultivars adapted to semi-arid regions would enhance yield gains and stability with desirable product profiles according to the needs of the farmers and the marketplace. Therefore, the overall objective of this study was to improve sorghum productivity in Nigeria by developing new generation, locally adapted and drought-tolerant varieties. The specific objectives of this study were to: (1) present the current opportunities and constraints to sorghum production in Nigeria and make recommendations as a guide to new variety design and sustainable production, (2) determine drought tolerance and genotype-byenvironment interaction (GEI) effect on grain yield of a population of African sorghum genotypes to identify high-yielding and drought-adapted genotypes for production and breeding, (3) assess the genetic diversity and deduce the population structure among 200 sorghum accessions to guide the selection of contrasting parents for pre-breeding and breeding of drought-tolerant sorghum cultivars and (4) determine the combining ability, heterosis and gene action conditioning agronomic traits and grain yield among sorghum genotypes to select genetically superior and contrasting parental genotypes and new families for drought tolerance breeding, cultivar release and commercialization. In the first chapter, a participatory rural appraisal (PRA) study was conducted in three selected sorghum growing zones in Northern Nigeria involving 250 farmers. Socio-economic data were collected through surveys and focus group discussions. Results showed that sorghum was cultivated mainly by males (80%) who had grade 6-12 level of education (31.3%), with a productive age of 21-45 years (75.7%) and a household family size of below five members (52.3%). Low-yielding landrace varieties such as Kaura (37.4%) and Fara-fara (29.3%) were the most widely cultivated types across the study zones due to their good grain quality. The major farmers' preferred traits from a sorghum variety were high yield, drought tolerance and Striga resistance. The study recommends integrated sorghum technology development incorporating the described preferences of the farmers for sustainable production and economic gains of the crop. The second chapter examined 225 sorghum genotypes assembled from diverse origins to determine drought tolerance and GEI effects on grain yield. The collections were evaluated under non-stressed (NS), pre-anthesis drought stress (PreADS), and post-anthesis drought stress (PoADS) conditions under field and greenhouse environments. The additive main effect and multiplicative interaction (AMMI) analysis revealed that genotype (G), environment (E), and GEI were significant (p<0.05) and accounted for 38.7, 44.6, and 16.6% of the total explained variation in grain yield, in that order. AMMI 4 was the best-fitting model for genotype selection with better grain yield. Based on AMMI 4 and the Best Linear Unbiased Predictors (BLUPs) analyses, genotypes Yar Lazau and Dangama Wulchichi, with a grain yield of 5.6 t/ha and 6.3 t/ha, were selected as being suitable for non-stressed conditions, respectively. Genotypes ICNSL2014-022-4 and Takumbo with BLUPs of 2.5 t/ha and 2.6 t/ha were best-suited for pre-anthesis drought stress conditions, whereas genotypes Danyar Bana and Gagarau - 4 with BLUPs of 4.2 t/ha and 4.3 t/ha are recommended for post-anthesis drought-prone environments, respectively. The identified sorghum genotypes are valuable genetic resources to develop novel drought tolerance cultivars or for production in dry agro-ecologies of sub-Saharan Africa characterized by pre-and-post anthesis drought stress. In the third chapter, diversity arrays technology (DArT) –derived single nucleotide polymorphism (SNP) markers were used to assess the genetic diversity and discern the population structure of 200 sorghum accessions to select complementary lines for breeding. The markers have moderate discriminatory power, with the polymorphism information content ranging between 0.09 to 0.38. The average gene diversity value (0.32) was high, while the average observed heterozygosity (0.15) was relatively low, a typical value for autogamous crop species like sorghum. The population structure and cluster analyses revealed four main clusters with a high level of genetic diversity among the accessions studied. The variation within populations (41.5%) was significantly higher than that among populations (30.8%) and between samples within a structure (27.7%). The high genetic variation within the population could be attributed to the preservation of sorghum landraces by farmers and differences in the genetic constitution, adaptation and parentage. The study identified distantly related sorghum accessions such as Samsorg 48, Kaura Red Glume (from Cluster 1); Gadam, AS 152 (Cluster 2); CSRO1, ICNSL2014−062 (Cluster 3); and Yalai, Kafi Mori (Cluster 4) useful in developing new gene pools and novel genotypes for the West and Central Africa (WCA) sorghum breeding programs. Based on the phenotypic and genotypic data, 12 contrasting parents were selected for breeding population development with high yield and drought tolerance. In the last chapter, 12 contrasting sorghum parents were selected from a diverse set of 225 genotypes exhibiting variable agronomic traits, including high grain and drought tolerance and farmer-preferred attributes. The 12 parents were crossed using a half-diallel mating design to create 66 F1 progenies. The F1 progenies, the parents, and two check varieties were evaluated under three environments in Nigeria. The results revealed the presence of significant variations amongst test genotypes allowing the selection of suitable parents and hybrids for traits of interest. The contribution of the specific combining ability (SCA) variance to total variance was higher than that of the general combining ability (GCA) for most of the studied traits, indicating that nonadditive gene action was more dominant in conditioning trait inheritance. GCA x environment and SCA x environment interaction effects were significant (p<0.05) for days to anthesis, aboveground biomass and grain yield. Parental genotypes Samsorg 7, Masakwa, and SSV2008091, recorded significant and positive GCA effects for grain yield and are useful germplasm resources for breeding high-yielding cultivars. Crosses AS 152 x SSV2008091, Samsorg 7 x Kurumbasau, AS 152 x ICNSL2014-022-8, and Masakwa x Hindatu exhibited high and positive SCA effects and were the top performers recording above-ground biomass yield of 29.3, 23.4, 27.2 and 16.5 t/ha and grain yield of 6.4, 6.6, 6.6 and 6.5 t/ha, in that order. The crosses exhibited high parent heterosis for grain yield and other agronomic traits, revealing that hybrid breeding is an effective strategy for boosting sorghum production. The newly selected F1 progenies had higher yields than the local checks and are recommended for hybrid or pure line breeding and variety release in Nigeria's drought-prone areas and similar sub-Saharan Africa (SSA) agro-ecologies after continuous selection and multi-environment testing. Overall, the study identified drought stress as the most critical sorghum production constraint in Northern Nigeria. Also, the study highlighted significant genetic diversity among the test genotypes. Best performing genotypes Yar Lazau, ICNSL2014-022-4 and Danyar Bana were selected as suitable for non-stressed, pre-anthesis and post-anthesis drought stress conditions, respectively. The selected genotypes are recommended for production or breeding in droughtprone areas. In addition, the study identified drought-tolerant and early-maturing genotypes (e.g., Samsorg 7, Masakwa, and SSV2008091) with good general combining ability effects for breeding population development and heterosis breeding in the semi-arid region of Northern Nigeria. IQOQA Amabele [Sorghum bicolor (L.) Moench] iyisivuno sokudla okuyinhloko esiphakela izigidi zabantu e-Afrika kanye ne-agro-ecologies eyomile necishe koma yase-Asia. Amabele atshalwa kakhulu eNyakatho yeNigeria, asetshenziselwa uchungechunge lwezinto ezahlukahlukene, kufaka phakathi imikhakha yokudla kanye nomkhakha wokuphiswa kotshwala. Kodwa-ke, ukukhiqizwa okungenzeka kanye nomkhiqizo wamabele e-Afrika, kufaka phakathi iNyakatho yeNigeria, kucindezelwa ukucindezeleka okukhulu kwesomiso okuhambisana nokuguquka kwesimo sezulu. Ngaphezu kwalokho, abalimi abancane eNigeria basalima amabele akhiqiza kancane nesezindaweni ezizwelayo esomisweni. Ukuthuthukisa kokutshalwa kohlobo lwamabele abekezelela isomiso ezifundeni ezomile kungathuthukisa ukuzuza kwesivuno nokuzinza ngamaphrofayili omkhiqizo ofiselekayo ngokwezidingo zabalimi kanye nendawo yemakethe. Izinhloso ngqo zalolu cwaningo zazithi: (1) ukwethula amathuba amanje kanye nezingqinamba zokukhiqiza amabele eNigeria futhi wenze izincomo njengesiqondiso sokuklama izinhlobonhlobo ezintsha kanye nokukhiqizwa okuqhubekayo, (2) ukunquma ukubekezelela isomiso kanye nomphumela wokusebenzisana kwegenotype-by-environment (GEI) ekuvuneni okusanhlamvu kwabantu be-African sorghum genotypes ukuhlonza amagenotypes aphezulu futhi avumelaniswe nesomiso sokukhiqiza nokuzala, (3) ukuhlola ukuhlukahluka kwezakhi zofuzo nokuthola isakhiwo sokusabalala phakathi kokufinyelela kwamabele angama-200 ukuqondisa ukukhethwa kwabazali abahlukile bokuzalanisa kwangaphambili nokuzalanisa amacultivars amabele abekezelela isomiso futhi (4) ukunquma ikhono lokuhlanganisa, iheterosis kanye nesenzo segene esilungisa izici ze-agronomic kanye nesivuno sokusanhlamvu phakathi kwamagenotypes amabele ukukhetha amagenotypes aphakeme ngofuzo futhi ahlukile wabazali kanye nemindeni emisha yokuzalanisa ukubekezelelana kwesomiso, ukukhululwa kwecultivar nokuthengisa. Esahlukweni sokuqala, ucwaningo lwe- participatory rural appraisal (PRA) lwenziwe ezindaweni ezintathu ezikhethiwe zokukhulisa amabele eNyakatho yeNigeria ezibandakanya abalimi abanga-250. Imininingwane yezenhlalo nezomnotho yaqoqwa ngokusebenzisa inhlolovo kanye nezingxoxo zeqembu lokugxila. Imiphumela ikhombise ukuthi amabele alinywa ikakhulukazi ngabesilisa (80%) ababenezinga lemfundo lebanga le-6-12 (31.3%), abaneminyaka ekhiqizayo yeminyaka engama-21-45 (75.7%) kanye nobukhulu bomndeni wasekhaya obungaphansi kwamalungu amahlanu (52.3%). Izinhlobo zomhlaba ezithela kancane ezifana neKaura (37.4%) neFara-fara (29.3%) zaziyizinhlobo ezitshalwa kakhulu kuzo zonke izindawo zokufunda ngenxa yekhwalithi yazo enhle yokusanhlamvu. Izici ezikhethiwe zabalimi abakhulu ezivela ezinhlobonhlobweni zamabele zaziyisivuno esiphezulu, ukubekezelela isomiso nokumelana neStriga. Ucwaningo luncoma ukuthuthukiswa kobuchwepheshe obuhlanganisiwe bamabele okufaka izintandokazi ezichaziwe zabalimi zokukhiqiza okuqhubekayo kanye nokuzuza kwezomnotho kwesivuno. Isahluko sesibili sihlole amagenotypes anga-225 amabele ahlanganiswe kusuka ezimvelaphini ezahlukahlukene ukunquma ukubekezelela isomiso nemiphumela ye-GEI ekuvuneni okusanhlamvu. Amaqoqo ahlolwe ngaphansi kwezimo ezingacindezelekile, ezinon-stressed (NS), ukucindezeleka kwesomiso sangaphambi kwe-anthesis, ipre-anthesis drought stress (PreADS), kanye nepost-anthesis drought stress (PoADS) ngaphansi kwezindawo zensimu kanye negreenhouse. Umphumela oyinhloko wesengezo kanye nokuhlaziywa kokusebenzisana kwemultiplicative (AMMI) kuveze ukuthi igenotype (G), imvelo okuyi-environment (E), ne-GEI yayibalulekile (p<0.05) futhi yaba ngama-38.7, 44.6, ne-16.6% wokuhlukahluka okuphelele okuchaziwe kwesivuno sokusanhlamvu, ngaleyo ndlela. I-AMMI 4 yayiyimodeli efaneleka kakhulu yokukhethwa kwegenotype ngesivuno esingcono sokusanhlamvu. Ngokusekelwe ekuhlaziyweni kwe-AMMI 4 kanye neBest Linear Unbiased Predictors (BLUPs), amagenotypes uYari Lazau noDangama Wulchichi, ngesivuno sokusanhlamvu se-5.6 t / ha ne-6.3 t / ha, bakhethwa njengabafanele izimo ezingacindezelekile, ngokulandelana. IGenotypes ICNSL2014-022-4 neTakumbo enama-BLUP we-2.5 t / ha ne-2.6 t / ha yayilungele kakhulu izimo zokucindezeleka kwesomiso sangaphambi kwe-anthesis, kanti amagenotypes Danyar Bana noGagarau - 4 nge-BLUPs ye-4.2 t / ha ne-4.3 t / ha kunconywa ezindaweni ezithambekele esomisweni ngemuva kwe-anthesis, ngokulandelana. Igenotypes yamabele ehlonziwe iyimithombo yofuzo eyigugu ukuthuthukisa amacultivars okubekezelela isomiso senoveli noma ukukhiqizwa kuma-agro-ecologies omile e-Afrika engezansi kweSahara ebonakala ngokucindezeleka kwesomiso sangaphambi kokuthunyelwe kwe-anthesis. Esahlukweni sesithathu, idiversity arrays technology (DArT) – nezimpawu amaderived single nucleotide polymorphism (SNP) kwasetshenziselwa ukuhlola ukuhlukahluka kwezakhi zofuzo nokuqonda isakhiwo senani sokufinyelela kwamabele okungama-200 ukukhetha imigqa ehambisanayo yokuhiqiza. Izimpawu zinamandla okubandlulula ngokulinganisela, ngokuqukethwe kolwazi lwepolymorphism okuphakathi kuka-0.09 kuya ku-0.38. Inani elijwayelekile lokuhlukahluka kwezakhi zofuzo (0.32) laliphezulu, kanti isilinganiso sabona iheterozygosity (0.15) yayiphansi kakhulu, inani elijwayelekile lezinhlobo zezitshalo ze-autogamous njengamabele. Isakhiwo senani kanye nokuhlaziywa kweqoqo kwaveza amaqoqo amane aphambili anezinga eliphezulu lokuhlukahluka kwezakhi zofuzo phakathi kokufinyelela kokufundiwe. Ukuhlukahluka ngaphakathi kwenani (41.5%) kwakuphakeme kakhulu kunalokho phakathi kwenani (30.8%) naphakathi kwamasampula ngaphakathi kwesakhiwo (27.7%). Ukuhlukahluka okuphezulu kwezakhi zofuzo ngaphakathi kwenani kungabangelwa ukulondolozwa komhlaba wamabele ngabalimi kanye nokwehluka komthethosisekelo wofuzo, ukuzivumelanisa nezimo kanye nokuba ngumzali. Ucwaningo luveze ukufinyelela kwamabele okuhlobene kude njengeSamsorg 48, i-Kaura Red Glume (kusuka ku-Cluster 1); Gadam, AS 152 (Cluster 2); CSRO1, ICNSL2014−062 (Cluster 3); noYalai, uKafi Mori (Cluster 4) owusizo ekuthuthukiseni amachibi amasha ezakhi zofuzo kanye namagenotypes amasha ezinhlelo zokuzalanisa amabele zaseNtshonalanga naphakathi ne-Afrika (WCA). Ngokusekelwe emininingweni yephenotypic negenotypic, abazali abayi-12 abaphikisanayo bakhethwa ukuthuthukisa inani lesivuno esiphezulu nesinokubekezelela isomiso. Esahlukweni sokugcina, imithombo eyi-12 eyahlukene yamabele yakhethwa esethini ehlukahlukene yamagenotypes anga-225 abonisa izici eziguquguqukayo ze-agronomic, kufaka phakathi okusanhlamvu okuphezulu nokubekezelela isomiso kanye nezici ezikhethiwe zomlimi. Imithombo eyi-12 yaxutshwa kusetshenziswa umklamo wokukhwelana wesigamu sediallel ukudala inzalo ye-66 F1. Inzalo ye-F1, imthombo, kanye nezinhlobo ezimbili zokuhlola zahlolwa ngaphansi kwezindawo ezintathu eNigeria. Imiphumela yaveza ukuba khona kokuhlukahluka okuphawulekayo phakathi kwamagenotypes okuhlola okuvumela ukukhethwa kwemithombo efanelekayo kanye namahybrid ezici ezithakazelisayo. Umnikelo ispecific combining ability (SCA) ukuhlukahluka kokuhlukahluka okuphelele kwakuphakeme kunalokho kwekhono igeneral combining ability (GCA) iningi lezici ezifundiwe, okubonisa ukuthi isenzo segene esingangeziwe sasibusa kakhulu esimweni sefa lesici. I-GCA x imvelo kanye ne-SCA x imvelo kwakubalulekile (p<0.05) ezinsukwini kuya ku-anthesis, ngaphezu kwebiomass yomhlaba kanye nesivuno sokusanhlamvu. Amagenotypes awumthombo i-Samsorg 7, i-Masakwa, ne-SSV2008091, aqophe imiphumela ebalulekile futhi emihle ye-GCA yesivuno sokusanhlamvu futhi ayimithombo ewusizo yegermplasm yokuzalanisa amacultivars aphezulu. Ukuxutshwa kwe-AS 152 x SSV2008091, i-Samsorg 7 x Kurumbasau, i-AS 152 x ICNSL2014-022-8, ne-Masakwa x Hindatu kubonise imiphumela ephezulu futhi emihle ye-SCA futhi yayingabadlali abaphezulu abaqopha isivuno se-biomass esingaphezulu komhlaba we-29.3, 23.4, 27.2 ne-16.5 t / ha kanye nesivuno sokusanhlamvu se-6.4, 6.6, 6.6 no-6.5 t / ha, ngaleyo ndlela. Ukuxuba kwabonisa iheterosis ephezulu yomthombo wesivuno sokusanhlamvu nezinye izici ze-agronomic, eveza ukuthi ukuzalanisa ihybrid kuyindlela ephumelelayo yokukhulisa ukukhiqizwa kwamabele. Inzalo esanda kukhethwa ye-F1 yayinesivuno esiphezulu kunokuhlolwa kwendawo futhi inconywa ukuzalanisa umugqa wehybrid noma ohlanzekile kanye nokukhishwa kwezinhlobonhlobo ezindaweni zaseNigeria ezithandwa isomiso kanye ne-agro-ecologies efanayo yesub-Saharan Africa (SSA) ngemuva kokukhethwa okuqhubekayo nokuhlolwa kwemvelo eningi. Sekukonke, ucwaningo lwaveza ukucindezeleka kwesomiso njengengcindezi ebucayi kakhulu yokukhiqiza amabele eNyakatho Nigeria. Futhi, ucwaningo lwaqhakambisa ukuhlukahluka okuphawulekayo kwezakhi zofuzo phakathi kwamagenotypes okuhlola. Amagenotypes enza kahle kakhulu uYar Lazau, ICNSL2014-022-4 noDanyar Bana akhethwa njengafanelekile ezimweni zokucindezeleka ezingacindezelekile, zangaphambi kwe-anthesis kanye nezimo zokucindezeleka kwesomiso ngemuva kwe-anthesis, ngokulandelana. Amagenotypes akhethiwe anconywa ukukhiqizwa noma ukuzala ezindaweni ezithambekele esomisweni. Ngaphezu kwalokho, ucwaningo lwaveza amagenotypes abekezelela isomiso futhi avuthwa ekuqaleni (isib., iSamsorg 7, iMasakwa, ne-SSV2008091) ngemiphumela emihle ejwayelekile yokuhlanganisa ikhono lokuthuthukiswa kwenani elizalayo kanye nokuzalanisa iheterosis esifundeni esomile saseNyakatho Nigeria.


Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.