Changes in responses to the inoculation of fungi by varying the number of subcultures of rice callus culture.

Authors recognized a decrease in morphogenetic potency of rice callus cultures by repeated subculturing. Based on this evidence, we investigated whether the rice callus cultures transferred from one to five times (F-callus) differed from that subcultured many times (M-callus) in its response to fungal infection. M-callus turned brown after 24 to 48hr by inoculation of Pyricularia oryzae and other plant pathogenic fungi. These fungi colonized favorably on M-callus. But growth of inoculated fungi on F-callus, with the exception of P. oryzae, was delayed in comparison with growth of fungi on M-callus. This evidence was based on the fact that F-callus formed the antimicrobial substances by the affection of fungi. But this activity was not so strong. However, there were no differences in growth of P. oryzae on both rice callus cultures. Quantity of polyphenols sligthly increased, but free o-diphenols were scarcely detected in both infected and noninfected rice callus cultures. Phenylalanine ammonia-lyase activity was increased in F-and M-callus by inoculation of P. oryzae and other fungi. No increase in respiration was observed in F-callus inoculated with fungi. Although tenuazonic acid caused the formation of necrotic spot on rice leaves which resembled of naturally infected one, callus surface was not changed at 50μg/ml of tenuazonic acid concentration, and callus growth was only inhibited with increasing concentration of it. We concluded from those results that R-gene actions in rice plant were not exhibited in rice callus cultures.