Low-Temperature Scanning Electron Microscope Observations of the Meloidogyne incognita Egg Mass: The Gelatinous Matrix and Embryo Development.

The root-knot nematode Meloidogyne incognita was cultured monoxenically on excised tomato roots. Galls and egg masses were observed daily using a light microscope. Two phases were distinguished in the gelatinous matrix of the egg mass: a translucent, amorphous material on the surface of the egg mass and a denser, layered phase in which nematode eggs were deposited. Egg masses were also cryofixed, fractured, and observed as frozen, hydrated specimens on a cold stage in a scanning electron microscope (SEM). In the SEM, the layered phase appeared as a meshwork of fibrils that became more loosely associated as the gelatinous matrix aged: Small pearl-like bodies were observed along the fibers of gelatinous matrix. The egg shell surface and several stages of embryo development, including the one-cell stage, initial cleavages, blastula, gastrula, tadpole stage, elongation, and molt of the first-stage juvenile within the egg shell, were observed and photographed with this technique. The developmental events observed were consistent with those described in other nematode species with different techniques.