Genotype environment interaction (GXE): effects on some major agronomic and rheological properties of cassava (Manihot esculenta, Crantz)

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Work was carried out to assess tuber yield, flour, gari and starch yields and their rheological properties in four elite varieties of cassava namely NKZ-009, NKZ-015, DMA-002 and WCH-037 selected from Brong Ahafo collections by Safo-Kantanka et al. (2000). Two sets of on-farm and on-station experiments were carried out. On-farm studies involved the four elite varieties grown at 18 locations in two years in the Transition and Forest ecozones. The on-station studies compared the performance of the above elite varieties with four improved varieties namely Abasafitaa, Ajisiafi and Gblemoduade which are IITA-based varieties developed by CSIR-Crops Research Institute and Tek-bankye which was developed by the Faculty of Agriculture, Kwame Nkrumah University of Science and Technology at two locations in two years. Data were collected on root tuber yield, harvest index, dry matter content, cooking quality, flour, gari and starch yields. Rheological data were collected on solubility, swelling power and water-binding capacity of flour and starch, and swelling capacity and pH of gari. The results from both experiments showed significant genotype x environment (GXE) interaction for all the traits studied. The age at harvest for maximum tuber yield did not coincide with that of flour, gari and starch yields. The performance of DMA-002 and WCH-037 was significantly better than the NKZ-lines for the agronomic traits but not significantly different for the rheological properties. The performance of the elite varieties was not significantly different from the released ones in any trait studied. Farmers seemed to have selected for varieties with high dry matter content since dry matter for the elite varieties was higher than the IITA-based improved varieties. However, dry matter did not have direct relationship with flour and gari yield. The presence of GXE interactions introduced complications into evaluation and selection for both agronomic and rheological characteristics among the cassava cultivars.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfillment of the requirements for the Award of MSc. Agronomy (Plant Breeding option) degree, 2005