Pathogenicity Determination of Crude Extract Toxin Produced by the Fungus Pyricularia oryzae Cav. Causal Agent of Rice Blast

Abstract

Series of experiments were carried out to determine the disease determinant factor of crude extract toxin produced by the rice blast fungus, Pyricularia oryzae, to determine an optimal concentration of crude extract toxin for screening against this toxin, and to obtain information on the phytotoxic effect of crude extract toxin on different varieties. The result indicated that crude extract toxin produced by P. oryzae was disease determinant factors. Leaf trated with this toxin produced spindle shaped to roundish lesion with gray centre and brown margin with or without halo and running lesion. The symptom was similar to those produced by the blast fungus infection. The capability of crude extract incited blast symptom increased when crude extract concentration increased. It was concluded that 25 percent concentration of the crude extract would be an appropriate concentration to inoculate rice plants. Genotypic variation was found among rice varieties against crude extract toxin inoculation. Varieties tested against crude extract toxin could be rated resistant, moderately resistant and susceptible to the toxin. The varieties produced small, roundish brown lesion with gray centre and without halo and running lesion were classified to be resistant whereas the varieties that produced larger round lesion with halo and running lesion were classified as susceptible. The result suggested that variety KTH-17 was considered to be susceptible whereas Usen was resistant.