The role of pore size on the migration of Meloidogyne incognita juveniles under different tillage systems

Migration of Meloidogyne incognita juveniles was investigated in soils collected from fields under different tillage regimes. Over 7 days, juvenile migration speed was greater in tilled soil (bulk density, 0.64 g cm−3) than in non-tilled soil (0.86 g cm−3). The volume of pores with diam. > 100 μm was greater in tilled soil than in non-tilled soil. The effect of bulk density on juvenile migration was investigated using columns filled with soils of six bulk densities (range, 0.60-0.85 g cm−3). As bulk density decreased, migration increased, and soil with a lower bulk density had greater volume of pores with diam. > 30 μm. The migration speed and behaviour of nematodes under saturated conditions were investigated using two micromoulded substrates that had pore spaces measuring 40-100 or 60-160 μm. As pore size increased from 40 to 160 μm, the migration speed decreased. The migration speed along a straight line ranged from 8.4 to 70.2 μm s−1 on these substrates. Migration speed was not constant across a pathway composed of different pore spaces, and the speed was affected greatly by the increased detection behaviour required in the broader space. Our experimental findings suggest that considerable nematode migration can occur in soil through pores with diam. 30-100 μm and > 100 μm. Therefore, conventional tillage may enhance the migration and reinfestation of crops by M. incognita.