Production of Zoospores, Mode of Infection, and Inoculum Potential of Pythium myriotylum Propagules on Cocoyam

Zoospores of Pythium myriotylum were consistently produced from sporangia of detached mycelia in vitro in deionized water at pH 7.0 with 0.001 M sucrose in 24 h of continuous fluorescent light at 31°C. The oblong-to-pea shaped zoospores measured from 2.5–7.5 μm in diameter and remained motile for more than 48 h. The lengths of flagella were 1–1.5 times the diameter of the zoospores. Contaminated cultures of P. myriotylum were revived to pure isolates by the use of zoospores. The penetration of P. myriotylum propagules took from 6 to 7 h following contact of the inoculum with the roots, and the invasion was inter- and intracellular. At the minimum concentrations of 200 zoospores/ml or 180 mycelial strands/ml, P. myriotylum caused symptoms of CRRD within 3 to 6 days after inoculation of the roots of cocoyam plantlets, results indicating that the pathogen is very destructive in cocoyam.