Michael A. McClure

Root-Knot Nematodes in Golf Course Greens of the Western United States

A survey of 238 golf courses in 10 states of the western United States found root-knot nematodes (Meloidogyne spp.) in 60% of the putting greens sampled. Sequence and phylogenetic analyses of 18S rRNA, D2-D3 of 28S rRNA, internal transcribed spacer-rRNA, and mitochondrial DNA gene sequences were used to identify specimens from 110 golf courses. The most common species, Meloidogyne naasi, was found in 58 golf courses distributed from Southern California to Washington in the coastal or cooler areas of those states. In the warmer regions of the Southwest, M. marylandi was recovered from 38 golf courses and M. graminis from 11 golf courses. This constitutes the first report of M. marylandi in Arizona, California, Hawaii, Nevada, and Utah, and the first report of M. graminis in Arizona, Hawaii, and Nevada. Two golf courses in Washington were infested with M. minor, the first record of this nematode in the Western Hemisphere. Columbia root-knot nematode, M. chitwoodi, was found in a single golf course in California. Polymerase chain reaction restriction fragment length polymorphism of the intergenic region between the cytochrome oxidase and 16S rRNA genes in the mitochondrial genome with restriction enzyme SspI was able to distinguish populations of M. graminis from M. marylandi, providing a fast and inexpensive method for future diagnosis of these nematodes from turf.

The tylenchid (Nematoda) egg shell: formation of the egg shell in Meloidogyne javanica

Oogonia of Meloidogyne javanica are radially arranged around a central rachis to which they are attached by cytoplasmic bridges. As the oocytes mature the rachis disappears and the oocytes pass through the oviduct in tandem. The oviduct-spermatotheca valve is constructed of two rows of tightly packed cells of which there are four per row. The nuclei of these cells are large and contain balloon-shaped cytoplasmic invaginations. The spermatotheca is characterized by microtubules which extend to its lumen and by invaginations of plasmalemma. Cells of the distal uterine region contain large intracytoplasmic spaces bordered by endoplasmic reticulum whereas proximal uterine cells have dense cytoplasm and large areas of compact endoplasmic reticulum. Egg-shell formation begins in the spermatotheca with the modification of the oolemma to form the vitelline layer. The chitinous layer begins in the distal portion of the uterus and appears to originate from the egg. Proline-containing protein is incorporated into the chitinous and lipid layers as the egg passes through the mid-region of the uterus and formation of the lipid layer in this region completes egg development.

Increased penetration of host roots by nematodes after recovery from quiescence induced by root cap exudate

Fourteen of 20 plant species surveyed produced root cap exudates that induced a state of reversible quiescence in Meloidogyne incognita and Caenorhabditis elegans. Exudate from six species failed to induce quiescence in either nematode species. Root cap exudates from pea were found to trigger quiescence in populations of plant-parasitic, animal-parasitic, insect-pathogenic, and free-living nematode species. One animal parasite was resistant. Caenorhabditis elegans strains with defects in known metabolic pathways also were screened to explore the potential for using this model system to examine the genetic basis for exudates-induced quiescence (EIQ). All 62 lines tested exhibited wild type sensitivity to root cap exudates and preliminary efforts to obtain viable EIQ-resistant strains by ethyl methanesulphonate (EMS) mutagenesis were unsuccessful. After recovery from EIQ, penetration of alfalfa roots by second-stage juveniles of M. incognita more than doubled within 24 h, compared with controls, and the number of nematodes per root remained high for a week but long-term development and maturation was similar to that of untreated control inoculum. In cucumber, penetration after recovery from EIQ increased by several fold but returned to control levels within 4 days post-inoculation.