Abstract
The spectrophotometer was used for the numerical evaluation of the relation between the tone of rice leaf color and the susceptibility to rice blast. It was able to evaluate precisely the numerical value of the seven tone grades of the rice leaf color scale by analyzing the brightness, coloration, tonality and reflection rate at 550nm wave length. It was also used for the evaluation of the relation between the tone of rice leaf color and the degree of susceptibility to rice blast after the nitrogen application as topdressing. It was able to detect the delicate change of leaf color just after nitrogen topdressing. Values of brightness, coloration and reflection rate at 550nm wave length reached the minimum 3 days after topdressing and the value of tonality reached the maximum. The susceptibility to rice blast began to increase just after nitrogen topdressing and reached the maximum 3 days later. These results suggested that using the spectrophotometer for detection of the change of leaf color afternitrogen topdressing was effective for the evaluation of the degree of susceptibility to rice blast.
