| Summary: | Thesis (M.Sc. (Agriculture, Plant Protection)) -- University of Limpopo, 2020 === The unavailability of environment-friendly nematicides for managing root-knot
(Meloidogyne species) nematodes in crop husbandry have led to various alternative
methods being sort which includes the development of cucurbitacin-containing
phytonematicides. The cited phytonematicides consistently suppressed nematode
numbers on different crops under greenhouse, microplot and field conditions, although
there is lack of information on how the products would affect susceptible Swiss chard
infected by root-knot nematodes. Swiss chard is one of most nutritious vegetables, grown
throughout the year and is well adapted to different soil types. However, these products
have the potential to induce phytotoxicity on various crops, if applied improperly.
Phytotoxicity of phytonematicides on different crops, has been resolved by deriving Mean
Concentration Stimulation Point (MCSP). The MCSP, developed using the Curve-fitting
Allelochemical Response Data (CARD) computer-based model, is crop-specific, hence it
should be developed for every crop. The objectives of this study were to investigate (1)
whether population densities of Meloidogyne species, growth and accumulation of
selected nutrient elements in Swiss chard would respond to increasing concentration of
Nemarioc-AL and Nemafric-BL phytonematicides under greenhouse and microplot
conditions and (2) whether the nemarioc-group and nemafric-group phytonematicides in
liquid and granular formulations would affect population densities of Meloidogyne species
and the productivity of Swiss chard with related accumulation of nutrient elements in leaf
tissues under field conditions. Parallel experiments for Nemarioc-AL and Nemafric-BL
phytonematicides were conducted concurrently under greenhouse and microplot
conditions. Greenhouse experiment was prepared by arranging 25-cm-diameter plasticpods on greenhouse benches, whereas microplot experiment was prepared by digging
holes and inserting 30-cm-diameter plastic pots in the field. The four-week-old Swiss
chard seedlings were transplanted into the pots, filled with steam-pasteurised loam, sand
and Hygromix-T at 3:1:1 (v/v) ratio. Treatments comprised 0, 2, 4, 8, 16, 32 and 64%
phytonematicides arranged in randomised complete block design (RCBD), with six
replications. Treatments were applied seven days after inoculation, with 3000 eggs and
J2 of M. incognita race 4 under greenhouse conditions, whereas under microplot
conditions were inoculated with 6000 eggs and J2 of M. javanica. Under field conditions,
treatments comprised untreated control (0), 2 g Nemarioc-AG and 3% Nemarioc-AL
phytonematicides (nemarioc-group) or 0, 2 g Nemafric-BG and 3% Nemafric-BL
phytonematicides (nemafric-group), arranged in RCBD, each experiment with 8
replications. At 56 days after initiation of treatments, eggs in roots, J2 in roots and Pf
exhibited negative quadratic relations under both greenhouse and microplot conditions.
Under greenhouse conditions, dry shoot mass (R2 = 0.81), dry root mass (R2 = 0.87) and
leaf number (R2 = 0.91) over Nemarioc-AL phytonematicide exhibited positive quadratic
relations. In contrast, dry shoot mass (R2 = 0.78), dry root mass (R2 = 0.93) and leaf
number (R2 = 0.70) over Nemafric-BL phytonematicide exhibited positive quadratic
relations. Under microplot conditions, dry shoot mass (R2 = 0.95) and gall rating (R2 =
0.96) over Nemarioc-AL phytonematicide, exhibited positive quadratic relations. Dry
shoot mass (R2 = 0.84) and gall rating (R2 = 0.97) versus Nemafric-BL phytonematicide
exhibited positive quadratic relations. Selected nutrient elements under greenhouse
conditions K (R2 = 0.96), Ca (R2 = 0.79), Mg (R2 = 0.64), Fe (R2 = 0.78) and Zn (R2 = 0.77) over Nemarioc-AL phytonematicide exhibited positive quadratic relations. In contrast, only Ca (R2 = 0.90), Mg (R2 = 0.68) and Zn (R2 = 0.84) over Nemafric-BL phytonematicide
exhibited positive quadratic relations, whereas K (R2 = 0.72) and Fe (R2 = 0.63) over the
product exhibited negative quadratic relations. Under microplot conditions, K (R2 = 0.82),
Ca (R2 = 0.90) and Mg (R2 = 0.98) over Nemarioc-AL phytonematicide exhibited positive
quadratic relations, whereas Fe (R2 = 0.91) and Zn (R2 = 0.79) over the product exhibited
negative quadratic relations. In contrast, K (R2 = 0.60), Ca (R2 = 0.68) and Zn (R2 = 0.95)
over Nemafric-BL phytonematicide exhibited positive quadratic relation, whereas Mg and
Fe over the product did not have significant relationships. Under greenhouse conditions,
MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides on Swiss chard were
3.03 and 2.36%, whereas overall sensitivity (∑k) values of the crop to the product were 3
and 0 units, respectively. In contrast, MCSP values of Nemarioc-AL and Nemafric-BL
phytonematicides on Swiss chard under microplot conditions was successfully
established at 3.71 and 3.33%, whereas the ∑k values were 2 and 1 units, respectively.
Under field conditions, at 64 days after initiating the treatments, the nemarioc-group
phytonematicides had highly significant effects on eggs in roots and reproductive potential
(RP), contributing 79 and 77% in total treatment variation (TTV) of the respective
variables. In contrast, the nemafric-group phytonematicides had highly significant effects
on eggs in roots and RP, contributing 67 and 76% in TTV of the respective variables.
Under field conditions, all plant growth variables were not significantly affected by the
treatments. The nemarioc-group phytonematicides had significant effects on K and Mg in
leaf tissues of Swiss chard, contributing nemafric-group phytonematicides had significant
effects on Mg, contributing 62% in TTV of the variable. In conclusion, the products could
be used on Swiss chard for managing population densities of Meloidogyne species.
However, due to the sensitivity of Swiss chard to the products, it would be necessary to
use the derived MCSP values to determine the application intervals of the products on
the test cultigen === National Research Foundation (NRF)
Agricultural Research Council (ARC)
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