Morphological adjustment in free-living Steinernema feltiae infective juveniles to increasing concentration of Nemafric-BL phytonematicide

Abstract

Third-stage larvae (L3) of Steinernema feltiae exist as free-living infective juveniles (IJ), with suspended development activities. In contrast, parasitic stages (L1, L2, L4, adult) have mutualistic relations with Xenorhabdus species bacteria, along with unique morphological changes and development inside the cadaver of host insects and/or plant-parasitic nematodes. Commercial IJ strains are tolerant to cucurbitacin-containing phytonematicides, but we have scant information on how morphological adjustments in IJ are achieved. In this study, we investigated the nature of morphological adjustments in commercial S. feltiae IJ strains to Nemafric-BL phytonematicide, which contains cucurbitacin B as active ingredient. Post-72 h exposure to phytonematicide concentration, IJ specimens were fixed on mounting slides. Length (body, excretory pore to anterior end, pharynx, rectum, stoma, tail), diameter (head width, neck base, mid-body, anal body), cuticle thickness and De Man ratios were measured with a computer software programme attached to Omax light microscope. Morphometric data against increasing phytonematicide concentration exhibited either densitydependent quadratic, linear or neutral relations. Increase in body length at low phytonematicide concentration was accompanied by decrease in tail length and pharynx length during muscle contraction when IJ were still alive. After death at high phytonematicide concentration, the opposite morphometric effects ensued due to muscle relaxation. The observed changes in morphometric structures were explained on the basis of morphological adjustments that modulated volumes of pseudocoelom cavity in IJ. The modulation is intended to maintain hydrostatic pressure within permissible upper limits in order to avoid structural damage to internal organs embedded in the pseudocoelom fluids. OPEN ACCESSCitation: Mashela PW, Shokoohi E, Pofu KM (2020) Morphological adjustment in free-living Steinernema feltiae infective juveniles to increasing concentration of Nemafric-BL phytonematicide. PLoS ONE 15(1): e0227448. https://doi.org/ 10.

Morphometric Adjustment in Meloidogyne enterolobii to Botanical Chemicals in Sorghum Cultivars with a Wide Degree of Pre-infectional Nematode Resistance

“…Broadly, a nematode is a "tube-in-a tube", with the outer tube being the multi-layered rather rigid cuticle, whereas the internal tube comprises a single-layered intestine [11,15,16,32]. The inner tube is technically embedded in a fluid referred to as the hydrostatic fluid, which induces hydrostatic pressure [16,32].…”

“…The inner tube is technically embedded in a fluid referred to as the hydrostatic fluid, which induces hydrostatic pressure [16,32]. Since the cuticle is rigid, when nematodes are exposed to solutions that increase the hydrostatic pressure in the pseudocoelom, adjustments of certain organs as illustrated by increases in length-related morphometrics avoid damage to internal organs by the increasing hydrostatic pressure [15,16]. The increase in length of certain morphometrics, supported by the existence of longitudinal muscles in J2 bodies [11,32], could to a certain degree, explain the observed increases in length-related morphometrics in this and other studies where infective stages of nematodes were exposed to increasing concentration of botanical chemicals [13][14][15][16].…”

“…In the mid-1980s, using inocula from a single egg mass, females of M. incognita developing on roots of 17 plants from seven genera, exhibited significant variation in morphometrics, except for females on non-host species, where the development to maturity was inhibited [12]. Recently, In vitro studies demonstrated that crude extracts containing cucurbitacins from fruits of wild Cucumis species consistently affect morphometrics Tylenchulus semipenetrans Cobb 1913 [13], Scutellonema brachyurus (Steiner 1938) Andrassy, 1958 [14], Steinernema feltiae Filipjev 1934 [15] and M. incognita [16].…”