Breeding of sweetpotato for improvement of root dry matter and β-carotene contents in Ethiopia.
Year: 2015
Type: dissertation
Abstract: Sweetpotato [Ipomoea batatas (L.) Lam] is the second major crop among the root and tuber \ncrops in Ethiopia contributing to food and nutrition security. Especially, the orange fleshed \nsweetpotato (OFSP) is a low-priced and sustainable source of vitamin A. It is useful to combat \nthe problem of vitamin A deficiency (VAD) prevailing in Ethiopia and most sub-Saharan \nAfrican countries. However, acceptance and adoption rate of the OFSP varieties by farmers is \nlow due to the low root dry matter content (RDMC) of the released OFSP varieties. Thus, \nimproving the RDMC of the OFSPs through breeding is vital to increase the adoption rate and \nthereby to improve vitamin A intake by the rural communities. Therefore, the objectives of the \nstudies were: (1) to assess and document the major constraints affecting production, pre- and \npost-harvest handling, and farmers’ preferences for sweetpotato in Ethiopia; (2) to determine \nthe combining ability, type of gene action and heritability of RDMC and β-carotene content, \nand yield related traits of selected sweetpotato clones, for further evaluation and breeding; (3) \nto estimate the magnitude of genotype-by-environment (G x E) interactions and to select \nstable and high yielding candidate sweetpotato clones for RDMC, β-carotene content and \nfresh root yield, and to identify the most discriminating and representative test environments \nin Ethiopia; (4) to assess associations between yield and yield related traits, and to identify \nthe most efficient yield-predicting traits in sweetpotato for effective selection; and (5) to \ndetermine the nutritional value of newly developed OFSP clones and to establish the \nassociations between β-carotene content and micro-nutrients for targeted large scale \nproduction to alleviate nutrient deficiencies. \nFirstly, a participatory rural appraisal (PRA) study was conducted in six selected districts from \nthree major sweetpotato growing administrative zones in southern Ethiopia involving 183 \nfarmers. PRA techniques including semi-structured interview, focus group discussions and \ndiscussion with key informants were used to collect data. The results indicated that \nsweetpotato is among the major crops grown in the study areas. According the respondents, \nthe major pre-harvest constraints were heat and drought (21.6% respondents), shortage of \nplanting materials (20.1%), shortage of land (15.7%), diseases (10.0%), insect pests (9.4%), \na lack of draft power (8.1%) and shortage of money to cover input costs (7.9%) were the \nmajor pre-harvest production constraints. The major post-harvest constraints were poor \naccess to markets (22.6% of respondents), poor market prices (19.1%), low yields (14.2%), \nlow root dry matter content (13.6%), a lack of knowledge on processing (11.7%), a lack of \nprocessing equipment (11.1%) and transportation problem (7.7%). The primary criteria for \nsweetpotato variety selection by farmers were identified as resistance to heat and drought (19.6% of respondents), RDMC (16.4%), taste (14.3%), root yield (13.6%) and, resistance to \ndiseases and insect pests (13.3%). \nSecondly, seven genotypes selected for their high RDMC, β-carotene content or fresh root \nyield were crossed using a half diallel mating design. A total of 28 genotypes: 21 crosses and \n7 parents, were evaluated at four locations in Ethiopia using a 7 x 4 alpha lattice design with \ntwo replications. Significant differences (p < 0.01) were observed among genotypes across \nthe four test environments for the following traits: RDMC, β-carotene, SPVD, fresh root yield \nand harvest index (HI). The general combining ability (GCA) to the specific combining ability \n(SCA) variance ratios were 0.96, 0.94, 0.74, 0.96 and 0.97 for RDMC, β-carotene content, \nSPVD, fresh root yield and HI, respectively, indicating that the inheritance of these traits was \ncontrolled mainly by additive genes. The following parents were considered good general \ncombiners for the three traits: Ukrewe and PIPI for RDMC; Ukrewe, Resisto and Ejumula for \nβ-carotene content and; Resisto and NASPOT-1 for fresh root yield. Good specific combiners \nwere the families belonging to Ukrewe x Resisto, Resisto x Ogansagan, Ejumula x PIPI and \nNASPOT-1 x Temesgen with high RDMCs of 36.6, 37.5, 38.2 and 37.2%; β-carotene \ncontents of 9844.7, 10590.3, 4685.6 and 5153.4 μg 100 g-1, respectively. Also, these crosses \nhad medium to high mean fresh root yields. Clones from these families were selected for \nadvanced selection and breeding for high RDMC, β-carotene content and root yield. \nThirdly, G x E interaction and stability analyses were conducted across six environments \n(Halaba, Kokate, Areka, Arbaminch, Hawassa and Dilla) in southern Ethiopia. A total of 24 \nexperimental clones selected based on their specific combining ability effects for RDMC, β- \ncarotene content and root yield along with one local check variety were evaluated. Superior \nand stable candidate clones, and suitable environments were identified using Additive Main \nEffects and Multiplicative Interaction (AMMI) and Genotype Main Effect and Genotype by \nEnvironment Interaction (GGE) biplot analyses. Accordingly, four candidate clones \ndesignated as G1 (Ukrewe x Ejumula-10), G6 (Resisto x Ejumula-7), G19 (Resisto x \nOgansagen-23) and G20 (Ejumula x PIPI-10) with above average RDMCs of 31.82, 32.60, \n33.09 and 30.06%; high β-carotene contents of 12.48, 14.27, 16.30 and 13.99 mg 100 g-1; \nand, stable and high fresh root yields of 25.09, 26.92, 21.30 and 25.46 t ha-1, in that order, \nwere selected for finishing off and recommendation. Among the sites covered in this study, \nArbaminch was identified as the best environment for sweetpotato testing or production in the \nsouthern Ethiopia with a high mean RDMC of 32.9%, mean β-carotene content of 7.2 mg 100 \ng-1 and the highest mean fresh root yield of 37.1 t ha-1. \nFourthly, correlation and path-coefficient analyses were conducted involving 24 newly \ndeveloped sweetpotato genotypes and one check variety using 15 quantitative traits. Root yield showed significantly positive correlations with most traits studied, indicating that \ncomponent characters should be simultaneously selected for sweetpotato improvement. β- \ncarotene content and root flesh colour showed a highly positive correlation (r = 0.76), \nsuggesting the importance of root flesh colour as an indirect selection criterion of high β- \ncarotene content in sweetpotato. With path-coefficients of 0.821, 0.776, 0.276, and 0.410, \nindividual root weight, number of roots per plant, RDMC and above ground fresh weigh had \nhigh positive direct effects on fresh root yield, respectively. These traits can be used for \nindirect selection to improve root yield. \nFinally, eight nutritional traits: β-carotene, protein, iron, zinc, starch, fructose, glucose and \nsucrose of the 25 newly developed sweetpotato genotypes were examined. The genotype \ndesignated as G8 (Resisto x PIPI-2) was the most promising with the highest contents of β- \ncarotene (20.01 mg 100 g-1), protein (7.08%), iron (2.55 mg 100 g-1), zinc (1.42 mg 100 g-1), \nfructose (4.45%), glucose (5.34%) and sucrose (16.20%) followed by the genotypes G15 \n(Resisto x Temesgen-23) and G19 (Resisto x Ogansagen-23). This shows the potential of \ndeveloping OFSP varieties enriched with these important micro-nutrients. \nThe present study revealed the possibility of breeding sweetpotato varieties that combined \nhigh RDMC, moderate β-carotene content, and high fresh root yields with wide or specific \nadaptation for large scale production in Ethiopia. Overall, the study assessed the major \nsweetpotato production constraints, developed valuable sweetpotato families with high \ncombining ability and heterosis for RDMC, β-carotene content and fresh root yield. Four traits, \nincluding individual root weight, number of roots per plant, RDMC and above ground fresh \nweight, were identified for indirect selection to improve root yield. The newly developed \ncandidate OFSP clones are good sources of vitamin A, iron and zinc with high levels of \nprotein and soluble sugars including sucrose, glucose and fructose.
Author: Fekadu Gurmu. Balcha
Language: English
Topic: Genetics and Plant Breeding
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2596178402