The Effect of Soil Moisture and Relative Humidity On the Root-Knot Nematode Meloidogyne Javanica 1)

Abstract

Stock cultures of M. javanica from Southern Rhodesia (S.R.) and Georgia (Ga) U.S.A., were established from single egg-masses. Egg-masses were used to study survival under extremes of soil moisture and relative humidity. Results are expressed in terms of galling on indicator plants. Two techniques for maintaining prescribed soil moisture levels (soil columns of varying height in glass cylinders and soil subjected to suction in sintered-glass funnels) gave comparable results. There was a greater and more rapid reduction in egg viability in wet soil (20.4 percent moisture) than in dry (3.4 percent moisture). The S.R. eggs withstood exposure to both wet and dry soil better than those of the Ga population. The more rapid reduction in viability in wet soil may be due to relatively quick hatching of eggs and increased activity of larvae in this environment, resulting in depletion of stored energy. Eggs of both populations died in atmospheric relative humidities of 0 and 20 percent for 1 day and 90 and 93 percent for 5 days. They withstood 100 percent humidity for 20 days. Viability of the Ga eggs was greatly reduced after 5 days, whereas S.R. eggs were relatively unaffected after 20 days. The tolerance differences of the M. javanica populations to extremes of soil moisture may be due to the different environmental conditions in the areas from which they were taken.