Induced soil suppressiveness to a root-knot nematode species by a nematicide

Investigations were conducted to determine whether the nematicide DiTera, could induce soil suppressiveness to the root-knot nematode Meloidogyne incognita. To determine the effects of DiTera on soil microorganisms with antagonistic potential to nematodes, DiTera was added to autoclaved and nonautoclaved soils, and at 10, 30, and 60 days after treatment (DAT), alginate screens with M. incognita eggs were buried in the soil for 70 h, removed, and incubated at 24 degreesC for 5 days to determine percentages of parasitized eggs and juveniles. At 30 and 60 DAT, the nonautoclaved soil treated with DiTera had higher percentages of parasitized eggs and juveniles than did the control, whereas no effects of DiTera were observed in the autoclaved soil. To further investigate the effects of DiTera on soil microbial communities, populations of specific groups of microorganisms from the soil and rhizosphere of tomato plants were quantified after DiTera addition. An increase in the population level of several groups of microorganisms from the soil and rhizosphere after DiTera treatment was observed 30 and 60 DAT compared with the control. Changes in traits of microbial physiology that confer enhanced survival or antagonism toward nematodes were also investigated; however, the application of DiTera was not correlated with a change in frequency of any one specific physiological trait. To investigate functional changes of the microbial community, activities of several soil enzymes including fluorescein diacetate hydrolysis, catalase, chitobiase, protease, and urease were measured along with pH and electrical conductivity from autoclaved or nonautoclaved soil treated with DiTera at 0, 2.5, or 5.0 g/kg soil after 1, 10, or 43 DAT. More enzymatic activity was measured as early as 1 DAT in the treatments with DiTera compared with the control. Our results demonstrate that application of DiTera to soil led to enhanced antagonism of root-knot nematodes and that this was associated with structural and functional changes of the rhizosphere bacterial community. (C) 2001 Academic Press.