Diseases of Cotton in Cordoba, Colombia

Meloidogyne incognita and Thielaviopsis basicola are important cotton pathogens in Arkansas (3). In fields where both pathogens are found, a synergistic interaction that dramatically increases losses may occur (5). Disease development for these pathogens differs including soil temperature and texture. Warm soil temperatures favor nematode damage, whereas cold soil temperatures increase black root rot severity (2). Co-infection expands the temperature ranges at which both pathogens are able to cause plant damage. The interaction appears to result in the fungus invading xylem tissue and causing extensive vascular necrosis (4). The objectives of this research are: 1) to evaluate the impact of soil texture on each pathogen and their interaction and pathogen survival; 2) to evaluate the impact of temporal and spatial separation of M. incognita and T. basicola on the disease interaction; 3) to examine the spatial distribution of both pathogens in the field and the importance of sampling frequency and pattern for estimating soil populations; and 4) to determine the influence of selected cultural practices on the severity and incidence of diseases caused by M. incognita and T. basicola and their interaction on cotton. The influence of soil texture will be evaluated in microplots and controlled environmental experiments. Five soil textures, ranging from 40 to 80% of sand, will be used in the microplot experiments. Pathogen population densities will be either 0 or 20 chlamydospore chains/g soil of T. basicola and 0, 4 or 8 eggs/cc soil of M. incognita.