Physiological Effects of Pentachlorobenzylalcohol on Rice Plants

Abstract

Pentachlorobenzylalcohol (PCBA) is a new fungicide remarkably effective against rice blast caused by Piricularia oryzae Cavara. It is known that PCBA has many desirable characteristics as a rice blast fungicide; for example, nonphytotoxicity for every variety of plants tested and extremely low toxicity for the rat, mouse and small carp. One of the most striking characteristics of PCBA in comparison with the organic mercury fungicides is the excellent residual effect. However the antifungal activity in vitro of PCBA against rice blast fungus is too weak to be regarded as the origin of the efficacy.To know the physiological function of PCBA on the rice plant, the influence of PCBA on the constituents of nitrogen and carbohydrate in the rice plant was studied. The change of the ratio of these organic constituents of the PCBA-sprayed rice plant and the unsprayed has been traced at successive growth stages.The results obtained was summarized as follows:1. Spraying of PCBA on the rice plant appeared to cause the decrease of the ratio of total nitrogen in the leaf blade. In ripening stage, however, the ratio of total nitrogen was estimated in higher level in the PCBA-treated plant than in the untreated.2. Concerning water soluble- and protein-nitrogeous fractions the results showed the similar tendency to that of the total nitrogen ratio. The compounds with amino radicals, especially glutamic acid and aspartic acid, decreased considerably after the treatment of PCBA, and were maintained in relatively low level till the later growth stage.3. In the carbohydrate fractions, the ratio of crude starch estimated in the lower sheath of the rice plant sprayed with PCBA was much higher than that of the unsprayed plant. There was also appreciable difference in the accumulation of crude starch in the ear between the PCBA-sprayed plant and the unsprayed.