| dc.description.abstract | Sweetpotato breeding clones from the Ugandan Regional Breeding Programme
that included exotic clones, locally selected clones, breeding lines and released cultivars
were evaluated together with their derived polycross progenies at Kakamega, Alupe and
Kabete in Kenya. The overall objective for this study was to assess the appropriateness for a regional sweetpotato breeding approach. This was achieved by determining the
heritability estimates, assessing the phenotypic variability and determining the relative
performances of clones and progeny families.
Trials composed of eighteen clones were established in three locations while trials
composed eighteen progeny families were established under four environments using the randomised complete block designs. Data was taken for nine characters namely, number of roots, fresh root yield, size of the roots, vigour of plants, foliage yield, root shape, root skin colour, root flesh colour and root dry matter contents. Estimates for fresh root yields, dry matter yields and foliage yields obtained were used to estimate parameters for comparison of stability among clones. Analyses of variance for the combined data for the clones revealed significant differences (p=O.O1) for all the evaluated traits. There were no significant differences among the sites for root dry matter contents, root skin colour and root flesh colour. Clone by sites interaction effects were significant for all traits except for root flesh colour, indicating a need for evaluation of these clones in individual locations for selection. Analyses of variance for the combined data showed that there were significant differences among proge~milies for the evaluated traits except for root shape, while locations were not significantly different for root shape, root skin colour and root flesh colour. Family by site interaction effects were not significant (p=O.05) for most of the traits except, for root flesh colour.
Significant effects (p=O.OI) for genotype by environment interaction were obtained
for fresh root, root dry matter and foliage yields for clones and not for progeny families.
Progeny families derived from imported progenitors, Hi-Dry and Papota had the highest
yields for fresh roots and root dry matter. The clone mean yields for the locations were
subjected to stability analysis and were ranked based on regression coefficient (b),
coefficient of determination (r2), standard error of slope (()2), error mean square (S2) and the mean clone yields. The most stable clones based on regression coefficient were No. 282 for root yield, No. 320 for dry matter yield and No. 277 for foliage yields. Based on r2, ri and S2,No. 178, Sowola and No. 282 were the most stable clones for fresh root, root dry matter and foliage yields respectively. Highest fresh root and root dry matter yields among the clones were obtained for No. 277 and No. 192 whereas Bikilamaliya and Bwanjule gave highest foliage yields. It was observed that standard error of slope and error mean square provided equivalent rankings of the clones and these were different from the rankings based on coefficient of determination and regression coefficient parameters.
Genetic variation attributable to clones was high (greater than 70%) for most of the
traits estimated indicating potential genetic variability in the breeding material for the
regional breeding programme. Selection among clones for improvement of these traits is therefore feasible. Variation attributable to derived progeny family groups was relatively
low with moderate environmental variance components except for root flesh colour and
root skin colour indicating slight distinction among the progeny family groups.
Heritability estimates by three different approaches indicated high broad-sense
heritability for parental clones (38-99%), conservative narrow-sense heritability estimates from parent-offspring regression analyses (0-50%) and moderate narrow-sense heritability estimates (20-94%) obtained from the partitioning of variance components of half-sib families. Consistently, relative high heritability estimates from the three approaches were obtained for root skin colour and root flesh colour that indicated potential progress in the respective selection schemes. However, relatively low heritability estimates were consistently obtained for root shape. High broad-sense heritability estimates indicate a wide variation attributable to genetic causes among the clones for the trial environmental conditions. The moderate heritability estimates from the half-sib families indicate a potential for half-sib-parent selection scheme in the sweetpotato improvement programme for these traits. The low parent-offspring regression analyses derived heritability estimates indicate an expected low response from inter-mating selected parents based on the performance means. Correlation results showed that most of the traits were either positively correlated or had no significant correlation. Selection for improvement therefore, of several of the evaluated traits is possible. It can therefore be concluded that the regional breeding programme is appropriate for improvement of the sweetpotato for the Kenyan sweetpotato production environments. Also, evaluation for progenies for parental selection could be done in single environmental condition due to the non-significant genotype by environment interaction. | en |
