TABLE CONTENTS

An Antarctic Nematode that Survives Intracellular Freezing
Wharton, D.A. (1), M.R. Raymond (1), S.R. Clarke. (2) & C.J. Marshall (2)
(1) Departments of Zoology and (2) Biochemistry, University of Otago, PO Box 56, Dunedin, NZ
Panagrolaimus davidi is a free-living Antarctic nematode that lives associated with moss and
algal growth in terrestrial coastal ecosystems of Victoria Land that are seasonally free of
snow and ice. Liquid water is available during part of the summer and the nematode is
exposed to an extremely variable thermal and hydric environment. P. davidi is the only
organism known to survive extensive intracellular freezing. However, depending on the
freezing conditions, this nematode may also lose water to the surrounding ice and survive by
cryoprotective dehydration. We have confirmed that P. davidi can survive intracellular ice
formation and shown that this ability is critically dependent upon the nutritional status of the
nematode. We have compared the structure of, and pattern of ice formation in, fed and
starved nematodes using light and electron microscope techniques. Results indicate a loss of
control over the pattern of ice formation in the starved nematodes. An ice-active protein
appears to be involved in controlling the formation and stability of ice in the nematode.
Attempts to purify the protein by binding to ice were not successful. This, and other results,
indicate that this protein is not an antifreeze protein but belongs to a novel group of ice-active
proteins, called recrystallization-inhibiting proteins. We hope to purify and sequence this
protein and determine the mechanism by which it interferes with recrystallization.
Survival of Plant-parasitic Nematodes in the Absence of a Host Crop
Moens, M. (1) & R.N. Perry (2)
(1) Institute for Agricultural and Fisheries Research, Burg. Van Gansberghelaan 96, 9820 Merelbeke, Belgium;
(2) Plant Pathology and Microbiology Department, Rothamsted Research, Harpenden, Herts. AL5 2JQ, UK
Plant-parasitic nematodes have evolved various strategies to survive adverse conditions when
host crops are unavailable. This talk will explore the various survival strategies of plantparasitic
nematodes to illustrate the adaptations necessary for survival outside the host plant.
The ability of species, such as Ditylenchus dipsaci and Anguina tritici, to survive extreme
desiccation is well documented and is associated with morphological and behavioural
adaptations of a specific stage in the life cycle. The survival of cyst and root-knot nematodes
as unhatched juveniles depends on the protection of the eggshell, perivitelline fluid and cyst
wall or gelatinous matrix. In all these instances, the nematode is in a dormant state, either in
diapause or quiescence. Soil dwelling stages of plant-parasitic nematodes have to survive the
intercrop period, often in adverse environmental conditions. Work on P. penetrans and M.
chitwoodi shows that survival of the two species in the intercrop period shows some
similarities but also some remarkable differences. Like P. penetrans, surviving stages of M.
chitwoodi are mainly detected in the root fraction. However, the survival dynamics of stages
in the soil differ. Unlike P. penetrans, whose distribution after harvest remains nearly
constant, the density of M. chitwoodi varies with the soil layer and also depends on the
previous crop. Our data showed no evidence of M. chitwoodi moving to deeper layers during
colder spells. Soil samples taken soon after harvest give highest detection for M. chitwoodi.
As the time after harvest increases, the numbers of juveniles in the soil decrease and detection
becomes more difficult. The possibility that these differences in survival behaviour of P.
penetrans and M. chitwoodi may, in part, be linked to different patterns of egg laying will be
discussed.
5 th International Congress of Nematology, 2008 51