A screen house experiment was conducted in 1000 cm(3) plastic pots to evaluate the effect of increasing population densities of M. incognita race 1 on yield of parsley cv. Double Curled. Initial nematode densities were: 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64, 128 and 256 eggs + second stage juveniles (J2) cm(-3) soil. Fitting the Seinhorst model, y = m+(1-m)z(Pi-T), to average plant top and total fresh weight and top dry weight, gave tolerance limits (7) of 0.17, 0.02 and 0.025 eggs + J2 cm(-3) Sod. The minimum relative yields (m) were 0.5 at Pi greater than or equal to 16 eggs + J2 cm(-3) soil, 0.55 at Pi greater than or equal to 2 eggs + J2 cm(-3) soil and 0.34 at Pi greater than or equal to 4 eggs + J2 cm(-3) soil for top fresh weight, total fresh weight and top dry weight. The maximum nematode reproduction rate was 37-fold at Pi = 0.25 eggs + J2 cm(-3) soil and an equilibrium density was estimated at 5 eggs + J2 cm(-3) soil. Anatomical modifications observed in galled roots were similar to those induced by this root-knot nematode species in other hosts.
