A. J. Clarke

Hatching of Cyst-Nematodes

This review primarily covers literature on the hatching of cyst-nematodes that has appeared since 1971. The section on physical factors which influence hatching includes the effects of temperature, moisture, aeration and seasonal effects especially in relation to diapause. Research dealing with chemical stimulation and inhibition of hatching is also reviewed and the mechanism of hatching is discussed with particular reference to Globodera rostochiensis.

Osmotic Stress and the Hatching of Globodera Rostochiensis

When hatched juveniles are transferred from distilled water to 0.4 M sucrose or trehalose solutions their water content falls from 72% to 67%, the value observed for unhatched juveniles in eggs equilibrated with water. Juveniles move little after 6 hr immersion in 0.4 M or more concentrated sugar solutions, but dilution with water to give a sugar concentration 0.1 M restores many to active movement. Few juveniles emerge from cysts in solutions of potato-root diffusate or of an artificial hatching agent (0.4 mM picrolonic acid) which contain sucrose at concentrations 0.4 M. The evidence suggests that loss of solutes from the egg fluid permits hatching and supports the belief that changes in permeability of the egg shell precede other steps in the hatching process. Prolonged storage of second-stage juveniles is possible in 0.4 M solutions of sugars.

Synthetic Hatching Agents for Heterodera Schachtii Schm. and Their Mode of Action

Two hundred and eighty-three compounds were tested for their hatching activity for Heterodera schachtii Schmidt, 31 of these, at the given concentrations, gave hatches equal to or greater than that obtained with beet root diffusate. No correlation was found between hatching activity and redox potential for the 25 redox compounds examined. The structure of the artificial hatching agents and the mechanism of hatching are discussed.

The Role of Trehalose in the Hatching Mechanism of Heterodera Goettingiana

Carbohydrate analysis of cyst components of Heterodera goettingiana revealed trehalose in the egg, mainly in the fluid surrounding the unhatched juvenile, at a concentration of 0.5 M. When hatched juveniles were transferred from artificial tap water or distilled water to 0.5 M trehalose their water content fell to 66.5 % , the value observed for unhatched juveniles in eggs equilibrated with water. Few juveniles moved after 7 d immersion in 0.5 M trehalose, but dilution with water to give a sugar concentration 0.1 M resulted in over 90% of the juveniles moving after 24 hr. Hatching was also inhibited when cysts were immersed in solutions of pea root diffusate containing trehalose to give a concentration of 0.5 M. This evidence, together with the increase in juvenile water content which occurs before hatching when eggs are immersed in pea root diffusate, suggests that loss of solutes from the egg fluid permits hatching. H. goettingiana shares some features of a hatching mechanism previously described for Globodera rostochiensis and Ascaris suum.

The Role of Egg-Shell Calcium in the Hatching of He Ter Odera Schachtii

The Ca2+ content of Heterodera schachtii egg-shells was investigated by X-ray microanalysis. The egg-shells contained Ca2+, most of which was probably present in the inner lipoprotein membrane. Results from experiments with artificial hatching and non-hatching agents suggested that hatching agents, by binding to or replacing membrane-bound cations, induced structural change in the membrane and hence altered egg-shell permeability to solutes. The results are discussed in relation to previous work on the hatching mechanism of Globodera rostochiensis.

Release of juveniles of cyst-nematodes from eggs by hypochlorites.

The release of juveniles from eggs of Globodera rostochiensis and Heterodera schachtii in hypochlorite solutions was of two chemical types. In dilute hypochlorite solutions ( 11.5, a second type of emergence occurred. Under optimum conditions 90-100% of the eggs released juveniles within 1h. Reported differences in the emergence of G. rostochiensis in bleaching powder and sodium hypochlorite solutions are largely related to the pH of the respective solutions and not to the cations present.