The interaction between Meloidogyne incognita and Thielaviopsis basicola on cotton (Gossypium hirsutum)

Studies were conducted to evaluate the relationship between the root-knot nematode (Meloidogyne incognita)(Mi) and black root rot ( Thielaviopsis basicola)(Tb) on cotton (Gossypium hirsutum ). Growth chamber studies at various temperatures were established with soils infested with Mi, Tb, or both. Reductions in plant height-to-node ratio and total fresh weight were observed for both pathogens compared to the control or soils infested with either pathogen alone. T. basicola reduced root galling and reproduction of the nematode. Histological studies showed that plants grown in Tb infested soil contained chlamydospore chains on the root surface and the fungus was not observed inside the vascular cylinder. Roots from soils infested with Tb and Mi showed bingal sporulation in and necrosis of vascular tissues. Microplot studies were used to examine the contribution of various populations of Mi and Tb to disease and cotton development. Combinations of Mi and Tb reduced plant survival and plant height-to-node ratios. Root necrosis was greater in the presence of either pathogen and was greatest for the higher rates of Mi and Tb. A reduction in Mi reproduction was observed at the high rate of Tb across all Mi levels compared to those plots without Th. Fields studies were used to evaluate the effects of chemical pesticides on both pathogens and plant growth. Recovery from soil and root colonization by Tb was lowered by soil fumigants. Plant height-to-node ratio and mid-season nodes above white flower was not affected by any of the treatments used. At harvest plant structure or yields were not affected by any treatment. These studies suggest that the pathogen combination expands the temperature range at which disease occurs and that Mi increases access of Tb to vascular tissues. Management of the nematode can be an important factor in minimizing the effect of this interaction on cotton production in Arkansas. The use of soil fumigants can lower root-knot nematode populations, and has the potential to decrease the severity of early season black root rot and indirectly reduce disease pressure the following growing season.