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Doctoral Degrees (Plant Breeding)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6633

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Browsing Doctoral Degrees (Plant Breeding) by Author "Achigan-Dako, Enoch Gbenato."

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    Breeding for high leaf yield and minerals content in Gynandropsis gynandra (L.) Briq.
    (2022) Houdegbe, Aristide Carlos.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
    Gynandropsis gynandra (Spider plant) is an African leafy vegetable rich in minerals, vitamins, and health-promoting compounds with great potential in addressing malnutrition. The species is used as food and medicine and provides substantial incomes for smallholder’s farmers with an increasing interest for its cultivation in Africa. Spider plant is also an important resource for pharmaceutical industries. However, its production is still hampered by low leaf yield, early flowering, pests and disease and poor seed germination, resulting from the lack of improved cultivars. Our study intended to develop high yielding and nutrient-dense cultivars for farmers through merging modern molecular and classical plant breeding tools to increase income generation and improve nutrition and health. Specifically, the study: i) assessed the phenotypic variability among advanced lines of spider plant using biomass and related traits; ii) profiled the leaf mineral content among advanced lines of G. gynandra; iii) determined the combining ability, gene action and heterosis of mineral content in spider plant; iv) identified the genetics of the inheritance of biomass and related traits in spider plant; and v) deciphered genomic regions associated with combining ability and heterosis of biomass and related traits in G. gynandra. The evaluation of 71 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa using biomass and related traits revealed significant difference among lines and principal component analysis grouped them into three clusters: Asia (Cluster 1), West Africa (Cluster 2), and East/Southern Africa (Cluster 3). The West and East/Southern African groups were comparable in biomass productivity and superior to the Asian group. Specifically, the West African group had high dry matter content and flowered early while the East/Southern African group was characterized by broad leaves and late flowering. The maintenance of lines’ membership to their group of origin strengthens the hypothesis of geographical signature in cleome diversity as genetic driver of the observed variation. The leaf mineral profile of 70 advanced lines of spider plant derived from accessions originating from Asia, East, Southern and West Africa revealed significant variation among lines and zinc, calcium, phosphorus, copper, magnesium, and manganese as landmark elements in the genotypes. East and Southern African genotypes were clustered together in group 1 with higher phosphorus, copper and zinc contents than Asian and West African lines, which clustered in group 2 and were characterized by higher calcium, magnesium and manganese contents. An additional outstanding group 3 of six genotypes (three, two, and one from Asia, Southern Africa and Eastern Africa, respectively) was identified with high iron, zinc, magnesium, manganese and calcium contents and potential candidates for cultivar release. Significant differences (P < 0.001) were observed among and between experimental hybrids and parents for the levels of all mineral contents. Significant general and specific combining ability effects together with variance components analysis revealed that both additive and nonadditive gene action controlled mineral content with a predominance of nonadditive gene action. Mid- and best-parent heterosis ranged from -84.98 and 404.79% for minerals. Parents with good general combining ability were identified, as well as crosses with high specific combining ability and heterosis. There were significant and moderate to strong correlations between mean hybrid performance, specific combining ability effects and heterosis levels and low to moderate correlations between general combining ability and mean parents’ performance. Similar to leaf mineral content, significant differences (P < 0.001) were observed among and between hybrids and parents for fourteen agronomic traits. Hybrids outperformed their parents with more than 50% for total and edible fresh biomass, showing the existence of hybrid vigour. Mid- and best-parent heterosis varied between -51.89% and 192.10% with only positive heterosis effects for leaf area and total fresh biomass, characterized by an average mid-parent heterosis greater than 50%. Significant general and specific combining ability (GCA and SCA) effects together with variance component analysis revealed that both additive and nonadditive gene action, controlled biomass and related traits in the species with the predominance of additive gene action. Moderate to high broad- and narrow-sense heritability was observed for most agronomic traits, except for dry matter content. The environment significantly interacted with genotype, GCA and SCA. Parents with good GCA and crosses with high SCA and heterosis were identified. There were significant changes from parents to hybrids in the association of harvest index and time to 50% flowering with biomass per plant and leaf traits on the one hand and between harvest index and dry matter content on the other hand. A core set of 594 diversity array technology sequencing (DArt-seq) markers were identified and differentiated the 38 parental lines into three clusters linked with the provenance of the original accession. Using this set of markers, a genome-wide association analysis revealed two markers linked to heterosis level for flowering time, a single marker for edible biomass, one marker for total fresh biomass and one marker for the number of primary branches. Specifically, the marker MABiomLa1 was a pleiotropic marker and was associated with heterosis level for biomass and leaf area. In contrast, no consistent markers associated with combining ability were observed for general combining ability and might be due to the low number of parents and the density of markers used. The study thus revealed that reciprocal recurrent selection would be a sound breeding strategy for G. gynandra improvement with the development of hybrid cultivars to exploit heterosis. These findings showed that G. gynandra could be used as a model plant to study the genetic mechanism underlying heterosis in orphan leafy vegetables. The identified markers open room for implementing marker-assisted selection in the species for better exploitation of heterosis.
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    Developing pre-breeding tools for the miracle plant [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: implications for genomic selection strategies optimization = Ukuthuthukisa amathuluzi okuzalanisa ngaphambilini esitshalo esiyisimangaliso [Synsepalum dulcificum (Schumach & Thonn.) Daniell]: imithelela yokuthuthukisa amasu okukhetha i-genomic.
    (2022) Tchokponhoué, Dèdéou Apocalypse.; Sibiya, Julia.; Achigan-Dako, Enoch Gbenato.
    The miracle plant [Synsepalum dulcificum (Schumach & Thonn) Daniell] is an evergreen orphan shrub species originating in West Africa that produces red berries known as miracle fruits. As a unique natural source of miraculin, miracle fruits stand as a singular natural sweetener with huge applications and economic potential. Unfortunately, the lack of systematic breeding history in the species currently hinders the full exploitation of the species potential at both the local and international levels. This study was undertaken with the goal of generating information that can be used to initiate a proper breeding and large-scale cultivation program of the species in its center of origin, West Africa, with a focus on three countries (Ghana, Togo, and the Republic of Benin). The objectives of the study were: i) to determine current management practices and end-users’ preferred traits to identify key breeding traits and formulate sound breeding objectives, ii) to evaluate the natural phenotypic diversity in the species to identify potential parental lines/populations for breeding purposes, to assess genomic diversity and population structure in the species to reshape breeding strategies, and to model the determinants of the local communities’ willingness to invest in the species cultivation to articulate promotion strategies in the species. To assess trait preferences by the miracle plant end-users (farmers, consumers, and processing companies) in the study area, semi-structured interviews and focus-group discussions were held with 300 individual respondents from various socio-cultural backgrounds and one processing company each in Benin and Ghana. The results revealed that farmers in Ghana currently manage the species better than their counterparts in Benin, with men being overall the main owners of the species. Our results offer an impetus for West Africa region-wide cultivar development, as both farmers’ and consumers’ preferences for breeding traits were >80% similar among the six sociolinguistic groups and the three agroecological zones considered in the study area. The preference for breeding traits was 60% similar among farmer, consumer and processing company user groups. Out of the 23 potential breeding traits identified in the study area, fruit size, fruit miraculin content, fruit yielding, early maturity, fruit edible ratio and seed part ratio represent priority breeding traits. Interestingly the traits (fruit size and miraculin content) were consistently ranked as the top two desired traits by all three end-user groups of the species. The classification conducted on 203 individual trees (accessions) sampled from seven populations in the Upper Guinea forest block (Ghana) and the Dahomey Gap (Ghana, Togo, and Benin) block revealed the existence of three natural phenotypic groups in the species. While in terms of population performance, the Volta population in the Dahomey Gap outperformed the six other populations for almost all the end-users’ desired traits assessed. Cluster 3, which encompassed accessions from all seven populations sampled, presented the best performance based on end-users’ preferences and, therefore, represents a potential source of elite accessions. Overall, variability ranged from low to moderate in traits evaluated [coefficient of variation: 9.65% (fruit length) – 53.34% (tree diameter at ground level] and the inferred core collection points to the Dahomey Gap as a center of diversity of the miracle plant. Despite the expected heterozygosity of HS = 0.14 suggesting a low diversity in the miracle plant, the molecular assessment done on 322 individuals revealed a strong population differentiation in the species (FST =0.69). Populations in the Upper Guinea forest block strongly diverged from those in the Dahomey Gap block, and our data supported the existence of a barrier (which we speculated to be the Lake Volta in Ghana) disrupting connectivity between those two West African rainforest block populations of the miracle plant. Corroborating the findings of the phenotypic assessment, the genome-wide diversity analysis also defined three genetic groups. Conveying a higher resolution to the population structuring, the genomic analysis highlighted an ecoregional structuring of the miracle plant population in the study area. The DNA polymorphism and demographic history analyses indicated the Western Dahomey Gap as the likely centre of origin of the miracle plant, thus refining the previously postulated West Africa origin of the species. The Volta population was confirmed as an exceptional breeding population with regards to its high allelic richness and heterozygosity. Our findings also suggest that sociolinguistic groups in Benin valued the miracle plant more than those in Ghana, to the extent that the species diversity was affected, as fitness organs such as roots and bark were highly targeted for medicinal uses. Nonetheless, these sociolinguistic groups in Benin were also more willing to engage in the miracle plant cultivation compared with those in Ghana. However, for this to be effective, market structuring and improved variety (early fruiting) development combined with awareness raising are needed to accelerate local community engagement in the species cultivation in the entire study area. Collectively, these results advance our knowledge of the miracle plant and form the basis for breeding initiatives in the species. The implications of these findings regarding optimization of a genomic selection strategy for accelerated genetic gains achievement in agronomic and functional traits of this species is discussed. Iqoqa Isitshalo esiyisimanga [Synsepalum dulcificum (Schumach & Thonn.) Daniell] wuhlobo lwembewu yesihlahla esingavamile esidabuka eNtshonalanga ne-Afrika, esaziwa ngokuthi siwumsuka ohlukile wemiracuin, isinandisi seglycoprotein esisetshenziswa ngezindlela ezahlukene. Yize kunjalo ukugqama kwaso kahle kukhinyabezwa ukungabi bikho kokuchuma kahle kwaso emlandweni wezimbewu. Lapha, injulalwazi emgwaqohlaka onezigaba zokuzalana kwale mbewu kuyacaciswa kanye nokubaluleka kokugxila esizindeni sokuqoqa ukuthuthuka kwaso ngenhloso yokuqondisisa, kwavezwa. Indlela enokubambisana yasetshenziswa ukuhlonza ubukhulu balesi sithelo, okuqukethwe yisithelo okuyimiraculin, ukuthela kwesitshalo, inani lokukhula kwesithelo, ukuvunwa kwesithelo singakashayi isikhathi, impilo yesitshalo eshalofini, kanye nobuncwaba besithelo njengezinto ezinqala ezidingeka ezitshalweni kulabo abazisebenzisayo eNtsonalanga ne-Afrika. Kwaqapheleka izinga eliphezulu elincamelekayo elifanayo lembewu, hhayi nje kuphela kubatshali, kepha nakubathengi bezitshalo ezahlukene ze-agroecological zones nakulabo abavela kwizindawonhlalo zolimi olwahlukene. Amaqoqo amathathu afanayo acwaningwa kulesi sitshalo eNtshonalanga ne-Afrika, kuphindelelwa ukusebenza kwaso kusezingeni eliphezulu u-0.8. Imiphumela yaveza iDahomey Gap njengomongo wokwehluka kwembewu. Le mininingo efuzene ibe isifakazelana ngesingle nucleotide polymorphism (SNP) markers eyizi-2704 iyinye. Yize-ke noma ukwehluka kwamamolekhyuli kube sezingeni eliphansi embewini (He = 0.14), kwase kuqina ukwehluka emiphakathini phakathi kwe-upper Guinea kanye neDahomey Gap, lokhu kwaze kwafakazelwa ukuhlaziywa KOHLAKA, okwaqagula ulibofuzo oluthathu esixhokweni esihambelana ne-Upper Guinea (UG), neWestern Dahomy Gap (WDG) neCentral Dahomy Gap (CDG). Imiphumela yethu yeseka umlando oguqukayo kulolu libofuzo lapho khona imiphakathi ye-UG ne-CDG kungenzeka ithole ukunwebeka kanti i-WDG iphakathi nendawo. Ekugcineni, yize noma imbewu yayiningi eGhana uma iqhathaniswa neBenin, amaqoqo enhlalolimi eBenin ayikhathalele imbewu kakhulu kunalabo baseGhana. Ulwazi olumangazayo ngembewu nobukhona bohwebo kuqaguleke njengezinye zezinto ezilawula inhlalosiko yokutshalwa kwale mbewu eNtshonalanga ne-Afrika. Le miphumela yethula ulwazi olubalulekile olungasetshenziswa ezinhlelweni zokuzalaniswa kwembewu.