Evaluation of the seed performance of cocoyam (Xanthosoma sagittifolium L. Schott) minitubers under the influence of poultry manure and NPK fertilizer

Abstract

The response of white and red cultivar (cv) cocoyam (Xanthosoma sagittifolium (L.) Schott) minitubers used as seeds was evaluated in different treatments. Poultry manure (PM) and NPK (20:10:10) fertilizer were applied. The experimental farm was situated at Ngog Bibega, Mbankomo Sub-division, Mefou and Afamba division, Centre region, Cameroon. Treatment combinations comprising of three rates each of PM (0, 20 and 30t.ha-1) and NPK (0, 120 and 150 kg.ha-1) were factorized and fitted into a randomized complete block design with three replicates. Physico-chemical analysis of all treatment plots revealed clay loam textures. Poultry manure treatment plots significantly (P<0.05) increased soil pH, organic content, total carbon and cation exchange capacity. At 6 months of culture of both cultivars, the agronomic parameters evaluated (average plant height, average leaf number and average leaf area) under poultry manure (30t.ha-1) treatments were higher compared to those of other treatments. Under the same treatments of poultry manure (30t.ha-1), the white cv plants recorded the highest mean yield parameters 9 months after planting among all treatments. For white cv plants, the average tuber number per plant was 8, average tuber weight was 250g, average tuber length was 14cm and average tuber girth was 18.5cm compared to the red cultivar average yield parameters; average tuber number per plant (5.7), average tuber weight (124.7g), average tuber length (8cm) and average tuber girth (14.5cm). The nutritional analysis of harvested tubers showed that red cv X. sagittifolium tubers (cormels) had a higher crude protein content than the white cv X. sagittifolium tubers for all treatments. Results obtained from the analysis of the macromineral content of harvested tubers showed that calcium, magnesium, sodium, phosphorus and nitrogen were higher in the red cv tubers than in the white cv tubers for all treatments. Biochemical analyses showed that the treatments tested, significantly (P<0.05) influenced the content of secondary metabolites evaluated in the leaves. Oxidase activities (peroxidases, polyphenol oxidase and glucanase) were evaluated in the different treatments. After 2 months of culture, plants treated with NPK (150kg.ha-1) expressed highest phenolic contents (1.22±0.13mg eq catechin. g-1 FW) and flavonoid contents (1.08±0.16mg g-1 FW) in white cv. After 6 months of culture, white cv plants treated with the poultry manure (30t.ha-1) epressed the highest protein content (5.04±0.38mg eq BSA.g-1 FW) and the most significant (P<0.05) peroxidase activity (4.89±1.36 UE min-1). On the contrary when white cv plants were treated with NPK (150kg.ha-1) fertilizer they recorded the most significant (P<0.05) polyphenol oxidase activity (4.99±0.10 in D330 nm-1. min-1 UE- 1. g-1 FW) after 6 months of culture. In the red cv plants treated with NPK (150kg.ha-1) fertilizer, glucanase activity the was most significant (P<0.05) (9.33±1.17 mg eq glucose g-1 FW) after 2 months of culture. HPLC-DAD-MS analyses permitted the identification of 8 flavonoid compounds in the leaf extracts of white and red cv plants under different fertilizer treatments. In all treatments our results illustrated two newly identified flavone C- glycosides (2 isomers of apeginin) and six known flavone C-glycosides (6, 8-Di-Cglucopyranosylapigenin, Isovitexin 6''-O-glucopyranoside, Apigenin 6-C-glucoside 8-Carabinoside, vitexin, isovitexin and. 2''-O-Malonylvitexin). After 6 months of growth, poultry manure treatments (30t.ha-1) enhanced flavone production in both cultivars compared to NPK fertilizer and control treatments. These results also showed: positive and significant correlations between growth and yield parameters, positive and non significant correlations between yield and biochemical parameters in both cultivars. Results obtained from this pioneering field trial of Xanthosoma sagittifolium minitubers, indicate that under certain conditions, these minitubers can serve as seeds to solve health problems linked to the use of tuber fragments as planting material