EFFECT OF TEMPERATURE ON THE INTERACTION BETWEEN BLACK ROOT ROT (Thielaviopsis basicola) AND THE ROOT KNOT NEMATODE (Meloidogyne incognita)

Both the root-knot nematode (Meloidogyne incognita) and the soilborne fungus that causes black root rot of seedling cotton (Thielaviopsis basicola) are widely distributed in cotton field soils in Arkansas. Both of these pathogens are capable of causing significant crop damage and yield loss, primarily through damage to the root systems of infected plants. When root-knot nematode or T. basicola infection occurs alone in fields, cotton plants may be damaged, but these pathogens seldom kill plants. In 1995, fields in Southeast Arkansas were found with extremely severe seedling disease problems that resulted in significant stand losses. In all cases, both the root-knot nematode and T. basicola were isolated from infected plants and from soil from the fields. Subsequent studies in microplots demonstrated the possibility that a synergistic disease complex occurred between these pathogens on seedling cotton, and the severity of the interaction appeared to be temperature-dependent. Growth chamber studies were conducted to determine the role of soil temperature in the severity of the interaction.