Cucurbitacin chemical residues, non-phytotoxic concentration and essential mineral elements of nemarioc-al and nemafric-bl phytonematicides on growth of tomato plants

Thesis(M.Sc.( Agriculture, Horticulture)) -- University of Limpopo, 2019

Worldwide, tomato (Solanum lycopersicum L.) is one of the most important crops grown for nutritional value and health benefits, and are highly susceptible to root-knot (Meloidogyne species) nematodes. Following the withdrawal of synthetic chemical nematicides, Nemarioc-AL and Nemafric-BL phytonematicides have been researched and developed as alternatives to synthetic chemical nematicides. However, Nemarioc-AL and Nemafric-BL phytonematicides contains allelochemicals namely, cucurbitacin A (C32H46O9) and cucurbitacin B (C32H46O8) as their active ingredients. Therefore, the objective of this study was to determine whether increasing concentration of Nemarioc AL and Nemafric-BL phytonematicides would result in cucurbitacin residues in tomato plant, to generate mean concentration stimulation point (MCSP) values, overall sensitivity (∑k) and selected foliar mineral elements of tomato plant. Two parallel trials of Nemarioc AL and Nemafric-BL phytonematicides were conducted under field conditions, with each validated the next season. Each trial had seven treatments, namely, 0, 2, 4, 8, 16, 32 and 64% of Nemarioc-AL or Nemafric-BL phytonematicide concentrations, arranged in a randomised complete block design (RCBD), with five replications. In each trial, the seasonal interaction on variables was not significant and therefore data were pooled across the two seasons (n = 70). In both phytonematicides, the cucurbitacin residues were not detected in soil and tomato fruit. Plant variables and selected foliar nutrient elements were subjected to the Curve-fitting Allelochemical Response Data (CARD) model to generate biological indices which allowed for the calculation of MCSP of phytonematicides on tomato and their ∑k values of tomato to Nemarioc-AL and Nemafric BL phytonematicides. In Nemarioc-AL phytonematicide experiment, MCSP for tomato plant variables was at 1.13%, with the ∑k of 60 units, while the MCSP for selected tomato nutrient elements in leaf tissues was at 2.49%, with the ∑k of 21 units. Plant height, chlorophyll content, stem diameter, number of fruit, dry fruit mass, dry shoot mass and dry root mass each with increasing concentration of Nemarioc-AL phytonematicide exhibited positive quadratic relations with a model explained by 95, 82, 96, 89, 83, 83 and 92%, respectively. Similarly, K, Na and Zn each with increasing Nemarioc-AL phytonematicide concentration exhibited positive quadratic relations with a model explaining a strong relationship by 91, 96 and 89%. In Nemafric-BL phytonematicide experiment, MSCP for tomato plant variables was at 1.75%, with the ∑k of 45 units, whereas MCSP for selected tomato nutrient elements in leaf tissues was at 3.72% with the ∑k of 33 units. Plant height, chlorophyll content, stem diameter, number of fruit, dry fruit mass, dry shoot mass and dry root mass and increasing Nemafric-BL phytonematicide concentration exhibited positive quadratic relations with the model explaining a strong relationship by 92, 83, 97, 96, 87, 94 and 96%. Likewise, Na and Zn each with increasing Nemafric-BL phytonematicide concentration exhibited positive quadratic relations with a model explaining their relationship by 93 and 83%, respectively. In contrast, K with increasing Nemafric-BL phytonematicide concentration exhibited negative quadratic relations with a model explaining the relationship by 96%. In conclusion, tomato plant variables and selected foliar nutrient elements over increasing concentration of phytonematicides exhibited DDG patterns, characterised by three phases, namely, stimulation, neutral and inhibition. The developed non-phytotoxic concentration would be suitable for successful tomato production under field conditions.