Host-parasite relationships of Meloidogyne incognita on spinach

Host–parasite relationships in root‐knot disease of spinach caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Nematode‐induced mature galls were large and usually contained one or more females and egg masses with eggs. Feeding sites were characterized by the development of giant cells containing granular cytoplasm and many hypertrophied nuclei. The cytoplasm in these giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density (Pi) in a series from 0–128 eggs and second‐stage juveniles per cm3 soil and growth of spinach cv. Symphony F1 seedlings was tested under glasshouse conditions. A Seinhorst model [y = m + (1 − m)zP–T] was fitted to fresh top‐ and total plant‐weight data for inoculated and control plants. Tolerance limits (T) of spinach cv. Symphony F1 to M. incognita race 1 for fresh top and total plant weights were 0·25 and 0·5 eggs and second‐stage juveniles per cm3 soil, respectively. The minimum relative values for fresh top and total plant weights were zero in both cases at Pi ≥ 32 eggs and second‐stage juveniles per cm3 soil. Root galling was least at low initial population densities and greatest at 16 eggs and second‐stage juveniles per cm3 soil. Maximum nematode reproduction rate was 33·1‐fold at the lowest Pi.