Van Deventer, C. S.Kanju, Edward Eneah2017-03-202017-03-202000-03http://hdl.handle.net/11660/5932English: 1. The study was undertaken to estimate genetic parameters like variance components, general and specific combining ability effects, phenotypic and genetic correlation coefficients, heritability coefficients, heterosis, genotype by environment interaction and genotypic stability for various characteristics of sweet potato. 2. Four male parents (Kenia, Brondal, Impala and Mafutha) were crossed in a factorial fashion with three female parents (Bosbok, Koedoe and Ribbok). The offspring and their parents were planted in three different environments at Roodeplaat, near Pretoria. One trial was planted under irrigation in 1998. The other two were planted in 1999 under irrigation and rainfed conditions, respectively. Twenty-five different agronomic and quality characteristics were measured. The computer program AGROBASE (1997) was used to perform the different analyses of variance such as the Line x Tester and additive main effects and multiplicative interaction, and correlations. 3. Significant differences were found among the averages of the parents and their offspring for nearly all characteristics except NMRW. The G x E interactions were significant for TRW, MRN, TSS, Hl, Pl, VC, lO, llT and Nl. Kenia and Mafutha were outstanding with regard to their high dry matter content. 4. The male parent Mafutha had the largest GCA effect for TRN (0.65), RFC (0.46), OMC (0.01) and HI (0.04). Impala had the largest GCA effect for TRN (0.75), Bosbok for RSC (1.55) and Kenia for OMC (0.02). No significant SCA effects were found between the crosses for economic important characteristics. 5. GCA: SCA ratios across environments for all root yield characteristics of economic importance were close to unity except for TRN with a ratio of 8.6. Extremely high GCA: SCA ratios were found for LLT (81.65), VC (61.56), La (54.12), PL (44.72) and VIL (39.25). 6. The VAIVG ratios were relatively high for most of the characteristics except for MRW (0.59) and TRW (0.68). 7. Larger heritability coefficients were found from the female parents for RSC, RO, LVP and PP. Combined narrow and broad-sense heritabilities estimated over both parents (h2 M+F) were negative for most economic important characteristics. Relatively high narrow-sense heritabilities were found for RFC (0.47), VL (0.46), VIL (0.46), LVP (0.45), La (0.48) and LLT (0.49). Narrow-sense heritability estimates by the parent-offspring regression method ranged from negative for NMRW and TRW, to 1.44 for PL. Among the characteristics of economic importance, OMC had the highest estimate (0.66) followed by RSC (0.57) and TRN (0.54). 8. Highly significant phenotypic correlation coefficients were found between OMC and TSS (0.75), TRN and MRN (0.86), VIL and VL (0.90), LLT and LO (0.84), NL and LO (0.83), NL and LLT (0.78), MRN and TRN (0.79), Hl and FW (-0.93) and HI and VL (-0.77). Extremely high and significant genetic correlations were found between TRW and MRW (0.92), LVP and NMRW (0.94), TRN and NMRN (0.88), Hl and TSS (0.94), TSS and VIL (0.91), TSS and NL (0.96), OMC and Hl (0.91), OMC and PP (0.93), OMC and LLT (0.97), FW and Hl (-0.91), Hl and LL (-0.95), VL and VIL (0.94), PL and FW (0.91), TRW and LL (0.91), VC and PP (0.93), LO and LLT (0.92) and between FW and LL (0.93). 9. Correlated response to selection indicates that selection for high HI is likely to increase MRW (0.02) and MRN (0.07 - 0.08). Furthermore, selection for long vines is likely to increase TSS (0.12 - 0.22), MRW (0.06), MRN (0.11), and TRW (0.08). 10.When combined across parents and environments, mid-parent heterosis was negative for all root yield and quality characteristics of economic importance except RO, which showed a positive heterosis of 12.9%. However, positive heterosis was found for individual crosses at some of the environments. 11.The AMMI stability value (ASV) showed that the parents were less stable than their crosses. The cross Koedoe x Impala was ranked first for MRN, Ribbok x Brondal for TRN, Ribbok x Kenia for MRW and Ribbok x Impala for TRW. The cross Koedoe x Impala showed significant levels of mid-parent heterosis for stability for MRN (-98.3%), Ribbok x Brondal (-89.5%) for TRN, Ribbok x Impala (-89.4%) for MRW and Ribbok x Impala (-95.4%) for TRW.Afrikaans: 1. Die studie is onderneem om die genetiese variansie-komponente soos algemene (AKV) en spesifieke kombineervermoë (SKV) effekte, fenotipiese en genetiese korrelasie koëffisiënte, ooreflikheidskoëffisiënte, heterose, genotipiese en omgewing interaksie en genotipiese stabiliteit vir verskeie kenmerke in soet patas te bepaal. 2. Vier manlike ouers (Kenia, Brondal, Impala en Mafutha) is gekruis in 'n faktoriale ontwerp met drie wyfie ouers (Bosbok, Koedoe and Ribbok). Die nageslag en hul ouers is geplant in drie verskillende omgewings by Roodeplaat naby Pretoria. Een proef is geplant onder besproeiing gedurende 1998. Die ander twee is gedurende 1999 geplant, die een onder besproeiing en die ander onder droëland toestande respektiewelik. Vyf en twintig agronomiese en kwaliteitskenmerke is bepaal. Die rekenaarprogram AGROBASE (1997) is gebruik om die verskillende ontledings soos Lyn x Toetser, additiewe hoofeffekte en meervoudige interaksie en korrelasies uit te voer. 3. Betekenisvolle verskille bestaan tussen die gemiddeldes van die ouers en hul nageslag vir naastenbyalle kenmerke, met die uitsondering van NMRW. Die G x E interaksies is betekenisvol vir TRW, MRN, TSS, Hl, PL, VC, LO, LLT en NL. Kenia en Mafutha is uitstaande met betrekking tot hul hoë droë materiaal opbrengs. 4. Die manlike ouer Mafutha het die grootste AKV effekte met betrekking tot TRN (0.65), RFC (0.46), DMC (0.01) en Hl (0.04). Impala het die grootste AKV effekte vir TRN (0.75), Bosbok vir RSC (1.55) en Kenia vir OMC (0.02). Geen betekenisvolle effekte bestaan tussen kruisings vir ekonomies belangrike eienskappe nie. 5. AKV: SKV verhoudings oor omgewings vir meester wortelopbrengs eienskappe van ekonomiese belang is baie na aan een behalwe vir TRN met 'n verhouding van 8.6. Uiters hoë AKV: SKV verhoudings is waargeneem vir LLT (81.65), VC (61.56), LO (54.12), PL (44.72) en VIL (39.25). 6. Die VANG verhouding was relatief hoog vir meeste van die eienskappe behalwe vir MRW (0.59) en TRW (0.68). 7. Groter oorerflikheidskoëffisiënte is verkry vanaf die wyfie ouers vir RSC, RO, LVP en PP. Gekombineerde nou- en breë-sin ooreflikhede vanaf beide ouers (h2 M+F) was negatief vir die meeste ekonomies belangrike eienskappe. Relatief hoë nousin oorerflikhede is waargeneem vir RFC (0.47), VL (0.46), VIL (0.46), LVP (0.45), LO (0.48) en LLT (0.49). Nou-sin oorerflikhede bereken vanaf die ouer-nageslag regressie metode varieer van negatief vir NMRW en TRW, tot 1.44 vir PL. Tussen kenmerke van ekonomiese waarde, het OMC die hoogste beramings (0.66) gevolg deur RSC (0.570) en TRN (0.54). 8. Hoogs betekenisvolle fenotipiese korrelasie koëffisiënte bestaan tussen OMC en TSS (0.75), TRN en MRN (0.86), VIL en VL (0.90), LLT en LO (0.84), NL en LO (0.83), NL en LLT (0.78), MRN en TRN (0.79), Hl en FW (-0.93) en tussen Hl en VL (-0.77). Uitermate hoë en betekenisvolle genetiese korrelasies bestaan tussen TRW en MRW (0.92), LVP en NMRW (0.94), TRN en NMRN (0.88), Hl en TSS (0.94), TSS en VIL (0.91), TSS en NL (0.96), OMC en Hl (0.91), OMC en PP (0.93), OMC en LLT (0.97), FW en Hl (-0.91), Hl en LL (-0.95), VL en VIL (0.94), PL en FW (0.91), TRW en LL (0.91), VC en PP (0.93), LO en LLT (0.92) en tussen FW en LL (0.93). 9. Gekorreleerde responsie op seleksie bevestig dat seleksie vir hoë Hl'n verhoging bewerkstellig in MRW (0.02) en MRN (0.07 - 0.08). Seleksie vir lang ranke is geneig om 'n verhoging in TSS (0.12 - 0.22), MRW (0.06), MRN (0.11), en TRW (0.08) te bewerkstellig. 10. Gekombineerd oor omgewings, was middel-ouer heterose negatief vir alle wortel opbrengste en kwaliteitseienskappe van ekonomiese belang, behalwe RO, wat 'n positiewe heterose van 12.9% getoon het. Ten spyte hiervan is positiewe heterose waargeneem vanaf individuele kruisings in sommige van die omgewings. 11.Die AMMI stabiliteitswaarde (ASV) toon dat die ouers minder omgewingstabiel is as die kruisings. Die kruising Koedoe x Impala is eerste geplaas vir MRN, Ribbok x Brondal vir TRN, Ribbok x Kenia vir MRW en Ribbok x Impala vir TRW. Die kruising Koedoe x Impala toon betekenisvolle vlakke van middel-ouer stabiliteit vir MRN (-98.3%), Ribbok x Brondal (-89.5%) vir TRN, Ribbok x Impala (-89.4%) vir MRW en Ribbok x Impala (-95.4%) vir TRW. 258.enSweet potatoes -- GeneticsSweet potatoes -- BreedingThesis (Ph.D. (Plant Breeding))--University of the Free State, 2000ThesisUniversity of the Free State