BEHAVIOR OF FUSARIUM-OXYSPORUM F SP VASINFECTUM ISOLATES FROM ANGOLA ON CALLUS-TISSUE OF COTTON

An experimental study was undertaken to determine whether inoculation of FOV on callus tissue of cotton would yield results comparable to those obtained with whole-plant tests, so the callus tissue technique could be used in lieu of those tests. Calli from embryos of 'Coker 304', a cotton cultivars known to be highly susceptible to FOV, and 'Acala SJC-1', known to be resistant, were cultured on amended MURASHIGE and SKOOG nutrient medium. Calli of 2 cm diameter were inoculated with 0.5 cm diameter disks of one of three isolates from Angola: Bie, Cuanza-Sul and Cuanza-Norte. Inoculated calli were examined every 5 h, and the following parameters assessed: colony growth rate, colony appearance, percentage of callus surface covered by the mycelium, branching of aerial hyphae, length of hyphae, and onset of necrosis. All parameters differed significantly between the cotton cultivars, but there were no differences between the FOV isolates. Some of the data suggested that the resistance of 'Acala SJC-1' was fungistatic against FOV. Tests at 20, 25, 30 and 35 degrees C showed a temperature of 25 degrees C to be optimal in all cases. The data were consistent with known results from whole plant tests; the dual culture in vitro technique can, therefore, be used as a rapid and reliable means also to study the FOV/cotton pathosystem.