Pathogenicity of the root-knot nematode Meloidogyne java']javanica on potato

Host-parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density (P) [0-64 eggs + second-stage juveniles (J2s) per cm(3) soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [y = m + (1 - m)z((P-T))] was fitted to fresh shoot weight and shoot height data of nematode-inoculated and control plants. Tolerance limits (T) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0.50 and 0.64 eggs + J2s per cm(3) soil, respectively. The m parameter in that model (i.e. the minimum possible y-values) for fresh shoot weight and shoot height were 0.60 and 0.20, respectively, at P = 64 eggs + J2s per cm(3) soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51.2 at a moderate initial population density (P = 4 eggs + J2s per cm(3) soil).