Sorghum-nematode interactions were previously purported to produce chemicals that confer pre-infectional nematode resistance to the infective second-stage juveniles (J2) of the root-knot (Meloidogyne species) nematodes in the rhizosphere, without any contact to J2 bodies. We tested the null hypothesis in four sorghum cultivars with a wide range of pre-infectional nematode resistance relative to the susceptible tomato cultivar. Post a 56-day exposure of Meloidogyne enterolobii, J2 from soil and root samples were subjected to step-wise fixative solutions and then mounted on slides. Length-related and diameter-related morphometrics were measured using an OMAX microscope – equipped with a digital measuring software. The study was conducted over two seasons and the seasonal interactions on morphometrics were not significant. Relative to the tomato cultivar, sorghum treatments generally increased the length-related morphometrics, but decreased the diameter-related variables in both soil J2 and root J2. The null hypothesis was therefore rejected in favour to the assumption that upon exposure of J2 bodies to botanical chemicals in both soil and root samples, with certain morphometrics being adjusted to ameliorate the potential damage of hydrostatic pressure on internal organs of the infective juveniles. In conclusion, in pre-infectional nematode resistance, J2 bridge chemicals in the rhizosphere and enter the root system, where chemicals still have effects on morphometrics of nematodes.

Cucurbitacin phytonematicides consistently suppress population densities of plant nematodes, but have no effect against bacteria, fungi and insects. This study investigates the mechanism through which cucurbitacin phytonematicides consistently exert nematicidal properties on nematodes. Post 72-h exposure of second-stage juveniles (J2) of Meloidogyne enterolobii to geometric concentration of Nemafric-BL phytonematicide, J2 total proteins were measured using TruspecCHNS Macro. Total proteins versus phytonematicide exhibited a negative quadratic relation (R² = 0.97), with the minimum total proteins achieved at x = 4.9% phytonematicide. Beyond the minimum, total proteins increased gradually, depicting the existence of both isoprenylation (breakdown) and farnesylation (biosynthesis) of total proteins. In conclusion, cucurbitacins and nematode cuticles are both chemically structured, which provides the mechanism through which the test chemicals consistently decrease population densities of plant nematodes.