Abstract
The rice plants treated with pulp-masses containing ethrel at more than 30ppm by spotting on leaves showed symptoms quite similar to the stunting of blast diseased plants, i.e., shortened new leaf blades and sheaths that emerged after infection, hastened leaf emergence period and epinasty of infected leaves. The ethylene evolution in susceptible cultivar inoculated with the blast fungus occurred immediately after infection and increased considerably toward eleventh day reaching the maximum level of 2.7nl/g/h, but decreased rapidly thereafter. Stunting of the plants was also induced as early as the latent period, becoming more conspicuous with disease development. In resistant cultivar the temporal evolution could be detected only two days after inoculation, resulting in no stunting. The leaves bearing acute type lesions with waterly greenish grey color produced much more ethylene than those with chronic type lesions with grey center and brown margin. There was no significant difference in the amounts of ethylene during the first 14 days that required for 1% inhibition of plant growth between the infected and the ethrel-treated plants. These facts suggest that ethylene may be a major factor for stunting of blast infected rice plants.
