PURPOSE:To provide a system for assaying the resistance of plants to disease- causative microorganisms and a method thereof. CONSTITUTION:The system is provided with the first and second stage 70 for placing one sample and the other sample where a plant to be assayed is divided into two samples; a sprayer 50 for inoculating a disease-causative microorganism to the one sample; the mean for leaving the other sample arranged in the second stage 70 and the one sample inoculated under the same conditions for a certain time; the first and second multiplier phototubes which are set so that they may face to these samples and measure the weak light emissions from them; and a computer 40 which compares the measurements of the first and second multiplier phototubes 10 to assay the resistance or sensitivity to diseases of the plant.
