Mean concentration stimulation point of nemarioc-AL and nemafric-BL phytonematicides on pelargonium sidoided : an indigenous future cultigen

Abstract

Pelargonium sidoides has numerous medicinal applications, with economic potential to serve as a future cultigen in smallholder farming systems. However, it is highly susceptible to the root-knot (Meloidogyne species) nematodes, without any identifiable nematode resistant genotypes. Nemarioc-AL and Nemafric-BL phytonematicides, with cucurbitacin A and cucurbitacin B active ingredients, respectively, are being researched and developed as an alternative to synthetic nematicides at the University of Limpopo. However, since active ingredients in phytonematicides are allelochemicals, the two phytonematicides have the potential of inducing phytotoxicity on crops protected against nematode damage. The objectives of the study, therefore, were (1) to determine the non-phytotoxic concentration of Nemarioc-AL phytonematicide on plant growth of P. sidoides, and (2) to determine the non-phytotoxic concentration of Nemafric-BL phytonematicide in plant growth of P. sidoides. Cuttings were raised in 30-cm-diameter plastic pots containing 10 000 ml steam-pasteurised river sand and Hygromix-T at 3:1 (v/v) under microplot conditions in autumn (March-May) and repeated in spring (August October) 2015. After establishment each plant was inoculated with 5 000 eggs and second-stage juveniles (J2s) of M. javanica. Six treatments, namely, 0, 2, 4, 6, 8 and 10% concentrations of each phytonematicide on separate trials were arranged in a randomised complete block design, with seven replicates. At 56 days after inoculation, in Experiment 1, Nemarioc-AL phytonematicide, treatment significantly (P ≤ 0.05) affected plant height, dry root mass and root galls, contributing 62, 69 and 70% to total treatment variation of the three variables, respectively. Relative to untreated control Nemarioc-AL phytonematicide increased plant height and dry root mass by 34 to 61% xxi

and 20 to 76%, respectively, with a slight decrease by 5% in plant height at the highest concentration. However, the material decreased root galls by 5 to 50%. Significant (P ≤ 0.05) plant variables were subjected to Curve fitting-allelochemical respond dosage model, to generate biological indices which were used to compute the mean concentration stimulation point (MCSP) using the relation: MCSP = Dm + Rh/2 and the overall sensitivity value (∑k). In Experiment 1, MCSP = 6.18% and ∑k = 3. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. Treatments reduced nematode variables, at all levels including at the lowest, but the effect were not different. In Experiment 2, Nemarioc-AL phytonematicide treatment effects were not significant on plant variables except for root galls, but were significant for root nematodes except for eggs. Data for plant variables in Experiment 2 were not subjected to Curve fitting-allelochemical respond dosage model because they were not significant (P ≤ 0.05). In Experiment 1, Nemafric-BL phytonematicide treatment significantly (P ≤ 0.05) affected plant height and root galls, contributing 63 and 67% to total treatment variation of the two variables, respectively. Relatively to untreated control, plant height was increased by 10 to 36%, while root galls was reduced by 2.43 to 60%. In Experiment 1, MCSP = 2.87% and ∑k = 3. Concentrations of Nemafric-BL phytonematicide significantly (P ≤ 0.05) reduced eggs, juveniles and Pf at all levels including at the lowest, but the effect were not significant different, with treatments contributing 78, 72 and 90% to the total treatment variation. In Experiment 2, Nemafric BL phytonematicide treatment effects were not significant on plant variables except for root galls, but were significant for root. In conclusion, Nemarioc-AL and Nemafric-BL xxii

phytonematicides could be applied at the lowest concentration of 2% where it was shown to be effective in suppressing population densities of M. javanica.