Host-parasite relationships in root-knot disease of white mulberry

Severe infections of white mulberry feeder roots and heavy soil infestation s by Meloidogyne arenaria race 2 were found in southern Spain. This is the first record of M. arenaria on white mulberry in Europe. Morphometric obser vations, analysis of the esterase electrophoretic pattern, and artificial i noculations of race differentials were used to characterize nematodes. Nema tode-induced mature galls were spherical and usually contained one or more females, males, and egg masses with eggs. Feeding sites were characterized by the development of giant cells that contained granular cytoplasm and man y hypertrophied nuclei. Giant cell cytoplasm was aggregated along a thicken ed cell wall. Vascular tissues within galls appeared disorganized. The rela tionship between the initial nematode population density (Pi) in a series f rom 0 to 1,024 eggs and juveniles/cm(3) soil and growth of white mulberry s eedlings was tested in the greenhouse. A Seinhorst model was fitted to plan t height and top fresh weight. Tolerance limits of white mulberry to M. are naria race 2 for plant height and top fresh weight were, respectively. 1.1 and 1.38 eggs and juveniles/cm3 soil. The minimum relative values for plant height and top fresh weight were 0 at Pi greater than or equal to 64 and P i greater than or equal to 128 eggs and juveniles/cm(3) soil, respectively. Maximum nematode reproduction rate was 435-fold at the lowest Pi.