The Effect of Soil Temperature On the Survival of the Root-Knot Nematodes Meloidogyne Javanica and M. Hapla 1)

Abstract

Plant roots infected with the root-knot nematode, M. javanica, were obtained from Southern Rhodesia, North Carolina and Georgia. These widely separated areas represent a diversity of soil temperature and soil moisture conditions. Stock cultures of each of the three populations, S.R., N.C. and Ga. were established from single egg-masses. Egg-masses of the three M. javanica populations and of M. hapla were exposed to various soil temperatures in the laboratory and to over-wintering in the field. Viability of eggs after treatment was measured by the bioassay method. At a soil temperature of -2° C eggs of M. hapla can survive for .a longer period than those of M. javanica. Of these populations S.R. has the least tolerance, N.C. has the greatest, and Ga. is intermediate. A longer period is required to kill eggs of all populations in dry soil than in damp soil. However, at 36° C and 40° C eggs are killed more rapidly in dry soil. The response of M. javanica and M. hapla to these high temperatures is the reverse of that found at -2° C, eggs of the latter are less tolerant than those of M. javanica. The N.C. eggs are least able to withstand high temperatures, those of S.R. are most tolerant and Ga. is intermediate. Individuals within each of the four populations exhibit increased tolerance to -2° C and others to 36° C. Tolerance to -2° C is not associated with response to high temperatures. The ability of M. hapla eggs to over-winter in the field is marked. Differences between the M. javanica populations are pronounced. Egg-viability of S.R. is greatly reduced after 98 days and none survived 139 days or longer. The N.C. eggs show only a moderate reduction in numbers after 98 days and some remain viable for 208 days. The Ga. population is intermediate, few eggs remaining viable after 139 days in the field. Differences of the degree of tolerance of the M. javanica populations may to some extent be due to conditions under which the three populations have evolved.