Production of zoospores, mode of infection, and inoculum potential of Pythium myriotylum propagules on cocoyam.
Zoospores of P. myriotylum were consistently produced from sporangia of detached mycelia in vitro in deionized water at pH 7.0 with 0.001 smallcap˜M sucrose under 24 h continuous fluorescent light at 31°C. The oblong-to-pea shaped zoospores measured 2.5-7.5 µm in diam. and remained motile for >48 h. Lengths of flagella were 1-1.5 times the greatest diam. of the zoospores. Contaminated cultures of P. myriotylum were revived to pure isolates by the use of zoospores. Penetration of fungal propagules took 6-7 h following contact with roots of Xanthosoma sagittifolium, and the invasion was inter- and intracellular. At a min. concn of 200 zoospores/ml or 180 mycelial strands/ml, P. myriotylum caused symptoms of cocoyam root rot disease within 3 to 6 d after inoculation of the roots of X. sagittifolium plantlets, showing the pathogen to be very destructive.