Effect of temperature treatments on the penetration and disease development in the leaf epidermis by the rice blast fungus, Pyricularia oryzae Cavara. 1. Effect of pre- and postdisposing temperature on the disease development of rice blast.

Four different pre- and postdisposing temperature regimes 23/15 C·23/15 C, 29/21 C·29/21 C, 23/15 C·29/21 C and 29/21 C·23/15 C were evaluated for their effects on percent penetration, hyphal growth and disease development by the rice blast fungus, Pyricularia oryzae, in the leaf epidermis of a susceptible rice variety Aichi-asahi. Typical leaf blast lesions produced more in 29/21 C·23/15 C plot than in other temperature treatments, but total number of typical lesions decreased as the length of duration of treatments became longer. On the contrary, total number of typical lesions increased by the longer duration of treatments in 23/15 C·29/21 C plot. Despite of the increase in percent penetration until 120 hours after inoculation, no significant differences were found for percent penetration among temperature regimes, but hyphal growth in the leaf epidermis and number of cells in which hyphal growth was observed were greatly influenced by temperature regimes; i. e., the seedlings disposed at 29/21 C regime after completion of inoculation exhibited apparent hyphal growth since 96 hours after inoculation, while hyphal growth was suppressed until 120 hours on the seedlings postdisposed at 23/15 C regime. Thus, lesion formation on the seedlings disposed at lower temperature after inoculation was delayed due to the suppressed activities of blast fungus after penetration.