ETHNO-BOTANICAL AND GENETIC VARIATIONS AMONG SWEETPOTATO ACCESSIONS GROWN IN MALAWI

Abstract

Sweetpotato (Ipomoea batatas L. Lam) is the second important root crop after cassava and one of the most widely grown crops for food and cash in Malawi. Production of the crop is done by small scale farmers in different environments where its lesser need for inputs gives it an important advantage over maize, the staple crop. Farmers grow many sweetpotato cultivars including landraces that are native in various communities but have not been exploited in the building up of a biological system capable of achieving a biological feasibility, consumer demand, and production economics in Malawi. Landraces contain some important traits, a genetic diversity that is useful for effective crop improvement. The location and measure of the extent of diversity in terms of indigenous knowledge, morphological, genetic, stability and nutritional variations among landraces is an important component in sweetpotato research and development. A study, which involved germplasm collection coupled with the compilation of indigenous knowledge was conducted in 2003 in some districts of the Northern (Chitipa, Karonga and Mzimba) and Southern (Nsanje, Chikwawa, Mulanje and Phalombe Districts) regions of Malawi. A total of 268 accessions were collected and planted at Bvumbwe Research Station during the 2004 and 2005 rainfall seasons for morphological, genetic diversity and nutritional analyses. An analysis of indigenous knowledge revealed that farmers who produce sweetpotato for subsistence grew 8.86 ± 4.34 of cultivars in one field. The cultivars which varied by names, phenotypes and attributes were grown in mixtures to satisfy various requirements as determined by environmental and socio-economic differences. Meanings of cultivar names, which varied between study sites, revealed important insights of sweetpotato attributes which formed the basis for cultivar selection. Farmers and meanings of names characterized cultivars by agronomic (yield, earliness to maturity, root size, root numbers etc.), post harvest (shelf life), gastronomic (taste, texture, aroma) and market (earliness to maturity, shelf life and gastronomic) values and differences. Use of seven morphological traits and ten SSR primers showed significant morphological and genetic variation (p< 0.05) among three eco-geographical populations namely the Northern, South Eastern and the Lower Shire Valley of landraces. The Shire Valley population which gave a Shannon Weaver diversity index of 0.67 on morphological traits and Nei’s genetic diversity of 0.37 on SSR markers exhibited highest morphological and genetic diversity implying an eco-geographical area for in situ conservation concentration. vi Multilocation trials showed larger effects of environment (62.86%) on sweetpotato root yield (t/ha) than the genotypes (14.25%). The elite genotype, LU96/303 was the most stable across six evaluation sites: Bvumbwe, Makoka, Chitedze, Chitala, Lunyangwa and Baka Research stations. The elite genotype LU96/334 was the least stable. The variation in performance of the genotypes in different locations and seasons implies cultivar selection for specific environments. Alternatively, there is need for concerted efforts in the development of stable genotypes that will suit the varying production environments. Nutritional assessment of 15 genotypes showed significant differences (p< 0.05) in concentration of β-carotene, vitamin C, iron, zinc and copper which were affected by storage root age and peeling. While cultivar Zondeni ranked the highest in β-carotene (13.93 mg/100g, unpeeled fresh roots), different genotypes attained different ranks for vitamin C, zinc, iron and copper. Naive and trained panels also ranked the 15 genotypes according to yield potential, texture, taste, aroma and colour suggesting farmers’ involvement in variety development.