Mean concentration stimulation point of nemarioc-AL and nemafric-BL phyonematicides on cururbita pepo cultivar 'caserata

Abstract

Butternut squash (Cucurbita pepo) is highly susceptible to root-knot (Meloidogyne species) nematodes. Nemafric-BL and Nemarioc-AL phytonematicides were being researched and developed for use in various crop farming systems for managing nematode numbers. However, the two products when not properly quantified are highly phytotoxic to crops. The Curve-fitting Allelochemical Response Dosage (CARD) computer based model was adopted to compute the Mean Concentration Stimulation Point (MCSP), which is a non-phytotoxic concentration. The objective of the study, therefore, was to determine whether the MCSP values of Nemarioc-AL and Nemafric-BL phytonematicides on squash under greenhouse, microplot and field conditions exist. Seedling were raised in 25-cm plastic bags filled with loam, pasteurised sand and Hygromix 2:1:1 (v/v) in the greenhouse , raised in 25-cm pots with pasteurised sand and loam 3:1 (v/v) on the microplot, and raised under field with Hutton sandy loam (65% sand, 30% clay and 5% silt). After establishment each plant was inoculated with 5 000 eggs and second-stage juveniles (J2) of M. incognita. Treatments comprised 0, 2, 4, 8, 16 and 32% concentration of Nemarioc-AL and Nemafric-BL phytonematicides with ten replicates. For greenhouse, treatments comprised 0.0, 0.8, 1.6, 3.2, 6.4 and 12.8% concentration of both Nemarioc-AL and Nemafric-BL phytonematicide with 10 replicates. For micro-plot and for field experiment treatments comprised 2.4, 4.8, 9.6, 19.2 and 38.4% of both Nemarioc-AL and Nemafric-BL with nine replicates. In all experiments, treatments were arranged in a randomised complete block design with ten replicates. In the greenhouse, Nemafric-BL phytonematicide had highly significant effects on dry fruit mass and significant on fruit number, but had no effect other plant variables recorded. xxii Treatments contributed 51 to 71% in total treatment variation (TTV) of dry fruit mass and fruit number, respectively. However, at higher concentrations the same phytonematicide decreased fruit number by 66 to 137% and dry fruit mass by 6 to 14%. In the greenhouse, MCSP value for Nemafric-BL phytonematicide was 2.83% of which the overall Σk was 3 units. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. In microplot, Nemarioc-AL was highly significant for dry shoot mass and dry fruit mass with treatment contribution of 15 to 63% in TTV. At lower concentrations Nemarioc-AL phytonematicide increased dry shoot mass by 5%. However, with increasing concentrations dry shoot mass decreased from 7 to 30%. Phytonematicide increased dry shoot mass from 41 to 81% and decreased root galls from 3 to 73%. In microplot, MCSP value was 11.85%, with the Σk zero. Plant variables and increasing concentration of phytonematicide exhibited quadratic relations. In field experiment, Nemarioc-AL and Nemafric-BL phytonematicide treatment effect were not significant on any plant variables. In conclusion, the MCSP and Σk values appear to be location-specific since they were not similar in various locations.