Studies on vine storage methods, planting techniques, paclobutrazol treatment, planting density and weevil management on sweetpotato (ipomoea batatas l.lam) cultivars promoted in South Africa

Hlerema, Igenicious Nicholas https://orcid.org/0000-0002-6111-404X

Title: Studies on vine storage methods, planting techniques, paclobutrazol treatment, planting density and weevil management on sweetpotato (ipomoea batatas l.lam) cultivars promoted in South Africa
Creator: Hlerema, Igenicious Nicholas https://orcid.org/0000-0002-6111-404X
Subject: Sweet potatoes
Subject: Seed treatment
Date Issued: 2019-09
Date: 2019-09
Type: Doctoral theses
Type: text
Identifier: http://hdl.handle.net/10353/21580
Identifier: vital:49336
Description: Sweetpotato (Ipomoea batatas L. LAM) is a major world staple food. It is a versatile, nutrient-rich crop well suited for production by emerging farmers, and thus a popular crop in subtropical parts of South Africa. The crop has several advantages such as producing more bioweight and nutrients per unit land area and per unit time than most other staple crops such as maize; adaptation to a broad range of agro-ecological conditions; and ability to compete and crowd out weeds, and affected by a relatively small number of pests and diseases. Root and vine yields achieved by emerging farmers are low and cultivation systems need to be optimized. The general objective of the research was to develop nursery practices that ensure a sustainable supply of sweetpotato planting materials and cultural practices that maximize yield, eating and nutritional quality of sweetpotato roots. The specific objectives were (i) to evaluate the effect of polyethylene and hessian bags on vine quality and vine survival period; (ii) to compare planting techniques and vine length; (iii) to determine the effect of paclobutrazol on storage root yield; and (iv) to evaluate the effect of Beauveria bassiana as biological control for sweetpotato weevil. The vine storage experiment aimed at identifying the best type of storage bags that keep the vines of “Bophelo”, an orange-fleshed sweetpotato cultivar in good quality for a longer period of time. The study involved two factors, viz storage bag type and storage period. The experiment tried to address (1) a sustainable seed system in sweetpotato and (2) production stimulated by cultural practises. Vines were stored in polyethylene bag without holes, polyethylene bag with 12 holes and dry hessian bag over 3, 6, 9, 12 and 15 days at an ambient temperature of 250C. The incremental cost-effectiveness ratio (ICER) was calculated to determine the cost-effectiveness of using the polyethylene bags with holes or without and the hessian bags. The results of the study showed that hessian bags store vines over a longer period (12 days) compared to the polyethylene bags without holes (6 days); however, hessian bags are more expensive. Polyethylene bags can still be used for transporting and storing vines if the farmer is within a short distance from the seed source and plants the vines within the 6 day period. Polyethylene bags with 12 holes are recommended since they allow maximum air circulation and extend storage period (9 days). Optimum planting techniques can help sweetpotato farmers to achieve optimal yields. Newly developed cultivars from the Agricultural Research Council have not been tested to determine the best planting techniques. A trial was conducted to investigate the effect of two planting orientations (horizontal and vertical) and different vine length (2, 3 and 4 subterranean nodes) of 3 released varieties, Blesbock, Bophelo and Ndou on storage root yield of sweetpotato. A factorial experiment was laid out in a randomised complete block design with three replications during two cropping seasons (2014/15 and 2015/16). The data collected in both experiments included total storage root yield, marketable storage root yield, and number of storage roots per size class. Significant differences were detected for the interaction of all factors on the number roots per size class, total storage root yield, and total average root weight. Vertical and horizontal planting per se showed no significance differences for all the sweetpotato root growth parameters such as total yield. However, the more the number of subterainian node the more yield we got for the commercial cultivar Blesbok. Paclobutrazol (PBZ) is a plant growth retardant hormone. This hormone might, therefore, be useful for sweetpotato growers to achieve higher plant populations per hectare because it would reduce the plant canopy. However, it should also be checked if the PBZ application does not affect nutrient content of roots and leaves, especially the beta-carotene content of the orange-fleshed cultivars. The objective of this study was, therefore, to determine the effect of PBZ on sweetpotato shoot growth, storage root yield and beta-carotene content of sweetpotato leaves and storage roots. The field trial was repeated over two seasons, namely 2014/15 and 2015/16 crop seasons. These field experiments were arranged as a split plot experiment. The main plots were allocated to four PBZ levels, laid-out as randomised complete block design, and treatment combinations of two cultivars (Bophelo and Blesbok) and two plants spacing (20 cm and 30 cm) were randomly allocated into the subplots. The PBZ levels applied were 0, 100, 200 and 300 mg of active ingredient per litre of water, sprayed 4 weeks after planting. Root yield and bioweight accumulation were recorded. In addition, a pot experiment was set up using cultivar Bophelo and 0 mg, 100 mg and 200 mg/l active ingredient of PBZ sprayed 4 weeks after planting. Leaf and root samples (150g and 400g of a composite sample respectively) were collected and analysed for total phenols, total flavonoids, vitamin C and beta-carotene. The field trial results revealed significant differences (P<0.05) in leaf and stem weight of the plants treated with different PBZ levels applied. The control (0 mg PBZ rate) had the highest leaf and stem weight. There were no significant differences in root yield among the PBZ levels. The results of leaf and root analysis for the Bophelo cultivar showed significant differences (P<0.05) in total phenols, total flavonoids, vitamin C and beta-carotene in leaf samples of the three levels of PBZ applied. The beta-carotene for the leaf increased at the 100 mg/l PBZ level. As the paclobutrazol level increased there was a reduction in the beta-carotene content for the roots from 18,91 to 13,97 to 10,77 mg/100g dry weight for 0 mg/l, 100 mg/l and 200mg/l, respectively. Application of PBZ to sweetpotato reduces the bioweight yield but does not have an effect on the root yield. Thus a higher plant density can be used to achieve higher yield and returns on investment. The leaves can be used as a relish and can be sold to supplement income. However, PBZ further reduces the beta-carotene content of the roots and is not recommended for use with orange-fleshed cultivars, where the objective is to enrich food with vitamin A. Sweetpotato weevils (Cylas puncticollis and C. formicarius) are notorious pests of sweetpotato. It causes severe losses in marketable root yield. The study tested the use of Beauveria bassiana (Balsamo Vuillemin) (Deuteromycota: Hyphomycetes) for controlling sweetpotato weevils. Experiments were conducted over two cropping seasons using four treatments: 1) dipping sweetpotato cuttings in solution of 1 g/litre B. bassiana before planting, 2) spraying with a registered chemical (Deltametrin) at 50 ml/100 litre of water starting 2 weeks after panting at biweekly basis for four months after planting, 3) spraying the leaves with B. bassiana (10 g/100 litre) starting 2 weeks on biweekly basis for four months after planting; and 4) control (sprayed with water). The research was arranged as split plot experiment, where the pest management treatments assigned to the main plots as per Latin square design and the three sweetpotato cultivars (Bophelo, Ndou and Blesbok) were randomly put in the subplot in each main plot. Spraying with B. bassiana significantly reduced the percentage of insect-damaged roots (9.95percent) compared to the control (22.48percent). Dipping sweetpotato cuttings in solution of 1 g/litre B. bassiana before planting did not significantly reduce the number of insect damaged roots (18.63percent insect damage). There was no significant difference between the chemical spray (8.2percent insect damage) and spraying with B. bassiana (9.95percent insect damage). The investigation indicated that B. bassiana can be considered as an alternative control method for the sweetpotato weevil. Use of biological control is less expensive and beneficial to reduce adverse effects on the environment and human health.
Description: Thesis (PhD) -- Faculty of Science and Agriculture, 2019
Format: computer
Format: online resource
Format: application/pdf
Format: 1 online resource (164 leaves)
Format: pdf
Publisher: University of Fort Hare
Publisher: Faculty of Science and Agriculture
Language: English
Rights: University of Fort Hare
Rights: All Rights Reserved
Rights: Open Access

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