GENETIC STUDIES OF ORANGE-FLESHED SWEETPOTATO (Ipomoea batatas [L.] Lam) FOR HIGH Β-CAROTENE, HIGH DRY MATTER CONTENT AND LONG SHELF-LIFE
Sweetpotato is an important food crop and has immense potential for nutrition security in Sierra Leone. However, the orange-fleshed (OF) types rich in β-carotene content and other antioxidants have been recently introduced in the country and the major source of concern in its production is the fresh storage root short shelf-life, which has been attributed to its low fibre and low dry matter contents, which are not preferred in Sierra Leone. The present study was conducted to develop orange-fleshed sweetpotato (OFSP) varieties that combine high β-carotene content, high dry matter content, fresh storage roots long shelf-life and high yield. Participatory Rural Appraisal (PRA) was conducted to identify farmers’ and consumers’ production constraints and preferences. Subsequently 190 accessions were collected and evaluated for phenotypic variation in Sierra Leone and 41 Ghanaian genotypes were screened in the minor and major seasons at Crop Research Institute, Kumasi to identify parental materials for breeding. Twenty of these genotypes with high yield potential, high β-carotene, dry matter and other quality traits were identified as cross compatible and were used in a polycross mating design for development of populations and to estimate genetic parameters for the considered traits. The production constraints listed by farmers during PRA comprised: low yield, post-harvest losses, prevalence of pests (weevil) and diseases, lack of healthy planting materials, drought, lack of extension services, lack of funds for large scale production, low market prices, lack of storage techniques and facilities. Preferred quality attributes included high yield, high dry matter content, long storage ability (shelf-life), tolerance to pests and diseases, early maturity, medium to large storage root sizes, red/purple skin colour, green petiole colour and round/almost divided medium size leaf for sauce. The PRA also revealed that farmers were aware of OFSPs which were recently introduced in Sierra Leone and cultivated by a few farmers in the Moyamba district. Farmers were aware of its nutritional values and exhibited the willingness to accept the variety. A variation of about 25.73% and 16.07%; 12.12% and 19.05% was obtained for the first and second components of morphological traits using Canonical and PCA mean Euclidean dissimilarity index respectively, indicating moderate diversity among the 190 Sierra Leonean sweetpotato germplasm. The genotypic variance component made the greatest contribution to sources of variation among the tested Ghanaian sweetpotato genotypes for most traits. Highly significant (p<0.001) differences existed among the genotypes for most of the considered traits in the three components of studies (field evaluations, physico-chemical analysis and storage screening). Sixteen discriminant phenotypic quality traits were identified which generated four genetic related clusters that comprised 13, 12, 6 and 10 genotypes respectively, with the distinctive features of high DM and starch, β-carotene and sugars, high flowering ability and lower storage weight losses. Moderate to high H2 values were observed for yield, storage and roots quality traits. The 20 genotypes selected as parent in the 3 components of studies included: Nanungungungu, Apomuden, Bohye, PGA14008-15, Otoo, PGA14011-13, Patron, CIP442162, PGA14008-22, PGA14008-9, CIP440390, Mother’sDelight, NKO3A, Obare, PGA14011-43, PGA14351-36, Sauti, Tu-orange, AP3A and BF59x CIP.4. One hundred and five (105) progeny evaluation trial was conducted at CRI Fumesua, Kumasi. Highly significant differences were observed among progenies for all evaluated traits. The best performing progeny for β-carotene ‘PG18295-J10’ (42.79 mg/100g f.w.b) obtained high dry matter content (29.36%), lower storage root weight loss (38.33%) after two months of storage and had high storage root/vine yields (14.50% and 10.50%) respectively. Progeny ’PG18305-J9’ performed highest for dry matter content with the value of 41.55%. ‘PG18385-J9’, ‘PG18353-J8’, ‘PG18295-J10’ and ‘PG18365-J2’performed best across the traits studied. Two best performing progenies ‘PG18295-J10 and PG18353-J8’ were observed to obtain undetectable starch contents and progenies ‘PG18329-J2, PG18128-J2 and PG18305-J9’ had no maltose contents, these can be exploited for non-sweet types of sweetpotato, a consumer preference in Ghana. The selected progenies could be advanced in multiple location trials for further evaluations in Sierra Leone and Ghana.