Effect of an ice-nucleating activity agent on subzero survival of nematodejuveniles

Juveniles of five species of nematodes, Caenorhabditis elegans, Panagrellus redivivus, Pratylenchus agilis, Pristionchus pacificus, and Distolabrellus veechi, were added to solutions with (treatment) and without (control) a c ommercial ice-nucleating activity (INA) agent. Ten-microliter droplets of t he solutions containing the juveniles were placed on glass microscope slide s and transferred to a temperature-controlled freeze plate where the temper ature was reduced to -6 to -8 degrees C. At this temperature, the droplets containing the INA agent froze while those without the agent remained liqui d. After 2 minutes, the temperature of the plate was raised to 24 degrees C , and the slides were examined with a light microscope to determine the via bility of the juveniles. The results showed that usually most juveniles (43 % to 88%, depending on species) in solutions that did not contain the INA a gent (controls) were active, indicating that the juveniles were capable of supercooling and were thereby protected from the subzero temperatures. Alte rnatively, less than 10% of the juveniles that had frozen for 2 minutes in solutions containing the INA agent remained viable, indicating that inocula tive freezing of the solution was lethal to the supercooled juveniles. Our results suggest that, in geographical areas where winter temperatures may n ot be sufficiently low or sustained to freeze soil, the addition of an INA agent may help induce ice nucleation and thereby reduce the populations of nematode species that are unable to survive when the soil solution is froze n.