Thesis (Ph. D. Agriculture (Plant Protection)) -- University of Limpopo, 2013 / Global withdrawal of synthetic fumigant and non-fumigant nematicides due to their ecounfriendly
impacts and high toxicity to non-target organisms, respectively, increased the
research and development of alternatives for managing population densities of plantparasitic
nematodes, particularly the root-knot (Meloidogyne species) nematodes.
Although Meloidogyne species had been managed using genotypes that are resistant to
plant-parasitic nematodes in various crops, various challenges negate the available or
introgressed nematode resistance. In tomato (Solanum lycopersicum) production,
nematode races and instability of nematode resistant genotypes under certain
conditions necessitated the continued research and development of alternatives since
most of the existing commercial tomato cultivars are highly susceptible to various
biological races of Meloidogyne species. The aim of the study was to research and
develop appropriate dosages of two phyto- nematicides which could be applied through
drip irrigation system in open field tomato production systems, while the specific
objectives were to: (1) determine whether a computer-based model could provide nonphytotoxic
concentrations to tomato plants using fresh fruits of wild watermelon
(Cucumis africanus) and wild cucumber (C. myriocarpus) under greenhouse conditions,
(2) determine whether computer-based concentrations from the two plant species when
using dried fruits would be less phytotoxic and more suppressive to nematodes, (3)
investigate application time intervals for the two products, (4) determine responses of
plant growth in tomato and nematode suppression in respect to the derived dosages,
and and (5) validate dosages of fermented crude extracts from the two plant species
with respect to plant growth of tomato and suppression of nematode numbers.
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Greenhouse, microplot and field studies were set to test the hypotheses intended to
achieve the stated objectives, with reliability of measured variables being ensured by
using statistical levels of significance (P ≤ 0.05) and coefficients of determination (R2),
while validity was ensured by conducting experiments at the same location over two
seasons and/or by setting up factorial treatments. Firstly, fermented plant extracts of
fresh fruits from C. africanus and C. myriocarpus consistently reduced population
densities of Meloidogyne species by 80-92% and 50-90%, respectively. Tomato plants
were highly sensitive to the two products as shown by the total degree of sensitivities
(Σk) and biological index of 0 and 3, respectively. Also, the mean concentration
stimulation range (MCSR) of 11% and 7% concentrations, respectively, attested to this
phytotoxicity. Secondly, fermented crude extracts of dried fruits from C. africanus and C.
myriocarpus also reduced population densities of Meloidogyne species by 78-97% and
87-97%, respectively. Tomato plants were highly tolerant to the two products in dried
form as shown by the total degree of sensitivities (Σk) and biological index of 4 and 3,
respectively. The MCSR values for C. africanus and C. myriocarpus dried fruits on
tomato were 2.64% and 2.99%, respectively, which for the purpose of this study were
individually adjusted to 3%, which translated to 36 L undiluted material/ha of 4 000
tomato plants. In subsequent studies, 3% concentration was used as the standard,
along with double strength concentration, namely, 6% concentration. Thirdly, the MCSR
values derived in Objective 4, namely 3% and 6% concentration for both Cucumis
species using the CARD model were used in the optimisation of application time interval
using the innovative concept of weeks (0, 1, 2, 3 and 4) in a 30-day month period.
Application time interval for 3% and 6% concentrations of C. africanus fruits was
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optimised at 2.40 and 2.61 weeks in a 30-day month period, respectively, which
translated to 18 days [(2.4 weeks/4 weeks) × 30 days] and 20 days [(2.6 weeks/4
weeks) × 30 days], respectively. In contrast, for both concentrations from fermented
crude extracts of C. myriocarpus fruits, application time interval was optimised at 16
days for 2.2 and 2.1 weeks, respectively. During optimisation of application frequencies,
fermented crude extracts from C. africanus and C. myriocarpus reduced final population
densities of M. incognita race 2 by 70-97% and 76-96%, respectively. Fourthly, optimum
application intervals (time), allowed computation of dosage, which is a product of
concentration and application frequency (dosage = concentration × application
frequency). Fifthly, validation of the dosages under open field conditions suggested that
6% × 16-day dosage under crude extracts from C. myriocarpus fruit significantly (P ≤
0.05) improved growth of tomato plants when compared with those of either 0%
(untreated control) or 3% at 16 days. In contrast, dosages of C. africanus fruit at two
application frequency had no effect on growth of tomato plants – suggesting that either
of the dosages was suitable for use in tomato production since both reduced nematode
numbers. During validation, the materials reduced nematode numbers by margins
similar to those observed previously under other environments. In conclusion, crude
extracts of the two Cucumis species have stimulatory concentrations which have
potential similar reductive effects on population densities of Meloidogyne species and
could serve as botanical nematicides. However, since plant responses to the two
products differed in terms of their respective dosages and active ingredients, it implied
that for further improvement of the two, the overriding focus should be on their
interaction with the protected plants and nematode numbers. Ideally, future research
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should include environmental impact studies, especially on the influence of the products
fruit quality of tomato, earthworms, fish and bees.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/1354 |
| Date | January 2013 |
| Creators | Pelinganga, Osvaldo Manuel |
| Contributors | Mashela, P. W., Mphosi, M. S., Nzanza, B. |
| Publisher | University of Limpopo |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xxxv, 183 leaves |
| Relation | Adobe Acrobat Reader, version 6 |
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