Thesis (M.Sc. (Plant Production)) -- University of Limpopo, 2013 / Two phytonematicides were researched and developed from fermented crude extracts
of wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus)
fruits for use as alternatives to methyl bromide in managing root-knot (Meloidogyne
species) nematodes in tomato (Solanum lycopersicum) production. Fruits of C.
africanus contain cucurbitacin B (C32H48O8), while those of C. myriocarpus contain
cucurbitacin A, which comprises cucumin (C27H40O9) and leptodermin (C27H38O8).
Phytonematicides from C. africanus and C. myriocarpus fruits are referred to as
nemafric-B and nemarioc-A, respectively. The two phytonematicides, due to their origin
from plant species with allelochemicals, have high potential of being phytotoxic to crops.
The use of the Curve-fitting Allelochemical Response Dosage (CARD) computer-based
model assisted in the establishment of concentrations which were stimulatory to growth
of tomato (Solanum lycopersicum) plants, while exhibiting nematoxic properties to
Meloidogyne species. The two phytonematicides were developed from crude extracts of
fruits dried at 52˚C in air-forced ovens and ground in a Wiley mill through 1-mm-opening
sieves. However, equipment for drying and grinding fruits would not be accessible to
smallholder farmers who wished to prepare their own products on-farm. The objective of
this study therefore, was to determine whether nemafric-BL and nemarioc-AL produced
from fresh fruit of the two Cucumis species would be suitable for use (i.e. non
phytotoxic) in tomato production for managing population densities of M. incognita race
2. In order to distinguish the products of fresh (F) fruits from those of dried (D) fruits,
they were code-named nemafricF-BL or nemariocF-BL and nemafricD-BL or nemariocD
AL, respectively, where G and L denoted granular and liquid formulations, respectively.
Tomato cv. ‘Floradade’ seedlings were infested with 3 000 eggs and second-stage
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juveniles of M. incognita race 2. An equivalent of 40 g and 80 g dried fruit mass of
nemafric-B and nemarioc-A, namely, 284 g and 411 g fresh fruit mass for nemafric-B
and nemarioc-A, respectively, were separately fermented using EMROSA effective
micro-organisms mixed with 16 L chlorine-free tapwater in 20 L container for 14 days at
± 25˚C, allowing pH to gradually decline to ± 3.7. Separate experiments for each
product run concurrently. Treatments, namely, 0, 2, 4, 8, 16, 32 and 64%
concentrations, where for instance, 2% = 20 ml/1000 ml x 100, were arranged in a
randomised complete block design, with 10 replications. Blocking in the greenhouse
was done for wind direction which was regularly erected by fans for cooling down the
greenhouse. At 56 days after weekly application of each treatment, flower number, fruit
number, dry shoot mass, dry root mass, dry fruit mass, plant height, stem diameter and
nematode numbers were each subjected to analysis of variance. Nematode data were,
prior to analysis, transformed using log10(x + 1), but untransformed data were reported.
Using the sum of squares, nemafric-BL and nemarioc-AL treatments affected dry root
mass, dry shoot mass, flowers number, fruit number, plant height and stem diameter.
Nemafric-BL contributed 67%, 78%, 58%, 43%, 60% and 26%, while nemarioc-AL
contributed 71%, 61%, 19%, 35%, 34% and 24% to total treatment variation of the six
respective variables. Plant variables with significant (P ≤ 0.05) treatment effects were
further subjected to the CARD model to generate seven biological indices, with three
distinct phases, namely, stimulation, neutral and inhibition phases. Using the quantified
stimulation phase, the mean concentration stimulation range (MCSR) was computed for
each variable using two biological indices, namely, threshold stimulation point (Dm) and
saturation point (Rh). The CARD model explained 98%, 99%, 98% and 98% of the
quadratic models of dry root mass, dry shoot mass, plant height and stem diameter,
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respectively, against increasing concentrations of nemarioc-AL. Similarly, the CARD
model explained 99%, 96%, 84% and 93% of total treatment variation in the respective
plant variables. The integrated MCSR [MSCR = Dm + (Rh/2)] for nemafric-BL on tomato
plants was 7%, while that for nemarioc-AL was 4%. In the CARD model, the overall
sensitivities (∑k) of tomato plants exposed to nemafric-BL and nemarioc-AL were 3
units and 5 units, respectively. Tomato plants were therefore, less sensitive to
nemarioc-AL since it had higher ∑k value than nemafric-BL. At 4% nemarioc-AL and at
7% nemafric-BL, the two phytonematicides were each highly suppressive to population
densities of M. incognita race 2. In conclusion, on the basis of non-phytotoxicity of the
computed MCSR values and their suppressive effects on population densities of M.
incognita race 2, the smallholder farmers could produce nemafric-BL and nemarioc-AL
phytonematicides on-farm. However, the production of the two products from fresh fruits
would not be sustainable since fruits of the two Cucumis species are highly seasonal
due to the high incidence of post-harvest decays. / The Land Bank Chair of Agriculture – University of Limpopo,
Limpopo Agro-processing Technology Station,and
the Flemish Interuniversity Council of Belgium
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/1673 |
| Date | January 2013 |
| Creators | Tseke, Pontsho Edmund |
| Contributors | Mashela, P. W., Mokgalong, N. M. |
| Publisher | University of Limpopo |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 65 leaves |
| Relation | Adobe Acrobat Reader |
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