Thesis (M.Sc. Agriculture (Agronomy) -- University of Limpopo, 2019 / Most sweet potato-producing regions in South Africa are heavily infested by the root
knot (Meloidogyne species) nematodes, which are difficult to manage since the
withdrawal of the highly effective fumigant synthetic chemical nematicides. Prior to
the withdrawal, the management of Meloidogyne species was not a priority in sweet
potato (Ipomoea batatas L.) production since methyl bromide was highly effective in
suppressing nematodes. The withdrawal resulted in the introduction of various
alternative nematode management strategies, with nematode resistance being the
most preferred. However, progress in the use of nematode resistance had been
hindered by limited information on accurate species identification since Meloidogyne
species have a wide host range and some biological races. The objectives of the
study were (1) to determine the degree of nematode resistance in sweet potato cv.
'Mafutha' to M. javanica, M. incognita races 2 and M. incognita race 4 and (2) to
investigate the mechanism of resistance in sweet potato cv. 'Mafutha' to M. javanica,
M. incognita race 2 and M. incognita race 4. A total of six Experiments were
conducted. In each, treatments comprised 0, 25, 50, 125, 250, 625, 1250, 3125 and
5250 eggs and second-stage juveniles (J2), arranged in a randomised complete
block design (RCBD), with six replications. Uniform rooted sweet potato cuttings
were transplanted in 20-cm-diameter plastic pots filled with steam pasteurised
(300˚C for 1 hour) loam soil and Hygromix-T mixed at 3:1 (v/v) ratio. At 56 days after
inoculation, plant variables and nematodes in roots were collected. Meloidogyne
javanica inoculum levels in Experiment 1 had highly significant (P ≤ 0.01) effects on
dry shoot mass and, stem diameter, contributing 74% and 50% in total treatment
variation (TTV) of the respective variables, whereas under M. incognita race 2
inoculum levels contributed 70% and 56% in TTV of dry root mass and dry shoot
mass, respectively. Meloidogyne incognita race 4 inoculum levels contributed 65%
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and 58% in TTV of stem diameter and dry shoot mass, respectively. In Experiment 2,
M. javanica treatment levels contributed 56% in TTV of dry root mass, whereas M.
incognita race 2 inoculum levels had no significant effect on any plant variable. In
contrast, M. incognita race 4 contributed 51% in TTV of vine length. In Experiment 1,
the nematode levels had significant effects on reproductive potential (RP) values,
with treatments contributing 96%, 86% and 76% in TTV of RP values in M. javanica,
M. incognita race 2 and M. incognita race 4, respectively. In Experiment 2,
treatments contributed 79%, 46% and 61% in TTV of RP values in the respective
Meloidogyne species. Results of the study suggested that growth of sweet potato cv.
'Mafutha' was affected by nematode infection, whereas the test nematodes were
able to reproduce and develop on the test potato cultivar. In conclusion, sweet potato
cv. 'Mafutha' was susceptible to M. javanica, M. incognita race 2 and M. incognita
race 4 and therefore, the cultivar should not be included in crop rotation programmes
intended to manage tropical Meloidogyne species and races in Limpopo Province,
South Africa. Since the cultivar was susceptible to the test nematodes, the study did
not evaluate the mechanism of resistance. / Agricultural Research Council (ARC),
National Research Foundation (NRF) and the Land Bank Chair of Agriculture
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/2957 |
| Date | January 2019 |
| Creators | Nkosi, Simangele Princess |
| Contributors | Mashela, P. W. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xx, 76 leaves |
| Relation | Adobe Acrobat Reader |
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