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 th ose obtained with whole-plant tests, so the callus tissue technique co uld 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-S ul 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 ae rial hyphae, length of hyphae, and onset of necrosis. All parameters d iffered 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 fro m whole plant tests; the dual culture in vitro technique can, therefor e, be used as a rapid and reliable means also to study the FOV/cotton pathosystem.