THE ROLE OF THE EGGSHELL IN THE COLD TOLERANCE MECHANISMS OF THE UNHATCHED JUVENILES OF GLOBODERA-ROSTOCHIENSIS

The eggshell of Globodera rostochiensis prevents exogenous ice nucleat ion during freezing and allows the eggs to supercool in contact with w ater. Hatched second stage juveniles (J2) are frozen by exogenous ice nucleation and are not freezing tolerant. The effect of low temperatur es on the hatching of eggs indicates that the unhatched J2 cannot surv ive freezing. The eggs exhibit a freeze avoiding strategy by supercool ing in the presence of external ice. There is no evidence for a cold-i nduced diapause. Exposure to high temperatures and to potato root diff usate does not destroy the ability of the eggshell to prevent exogenou s ice nucleation; indicating that this is not a property of the lipid layer of the eggshell. Exposure to 10% NaOCl, however, does destroy th is ability and is accompanied by a pronounced thinning of the eggshell . This suggests that the prevention of exogenous ice nucleation is a p roperty of the chitinous layer of the eggshell.