Effect of inoculum concentration, wetness duration and plant age on disease development by Exserohilum prolatum in itchgrass (Rottboellia cochinchinensis)

Hala E. Alloub, A. S. Juraimi, J. Kadir, A. Rajan, S. Sasttroutomo


Exserohilum prolatum, a fungus isolated from diseased itchgrass plants in Peninsular Malaysia, has been considered as a potential agent for biological control of this serious grass weed. Inoculum concentration, wetness duration and itchgrass age significantly influenced disease development by E. prolatum in itchgrass when evaluated in glasshouse experiments. Disease development increased with increasing inoculum concentration from 2x104 to 2x107 conidia/ml. As wetness duration increased, disease development increased. Complete kill of itchgrass at 3 to 4 leaf stage was obtained at 2x106 conidia/ml and a 24 hr dew period. However, when formulated in 0.01% Tween 20 and 2% palm oil, E. prolatum reduced wetness duration requirement, and exposure to 12 hr dew period resulted in 80% reduction in itchgrass shoot dry weight. Susceptibility of itchgrass to the fungus decreased with increasing plant age. Itchgrass at two to six leaf stages were the most susceptible to fungus infection.

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