Abstract
In order to clearify the mechanism of phytotoxicity against rice plants caused by soil treatment of simetryne, the effects of several enviromental conditions, especially the air humidity, to the phytotoxic symptoms and to the content of simetryne in rice plants were investigated.
Simetryne was applied on the watersurface of submerged soil after transplanting the rice seedlings. The results are as follows.
1. Necrosis of lower leaves of main stem and of tiller leaves was the main symptom of simetryne phytotoxicity at the early stage, thereafter these symptoms were observed in upper leaves. Dry weights and number of tillers of rice plants reduced remarkably by simetryne application. The degree of those reduction showed good relation with the applied dose of simetryne and with the saturation deficit.
2. The content of simetryne in rice plants was higher at lower humidity and in lower leaves than at higher humidity and in upper leaves. The degree of phytotoxicity was closely related with the content of simetryne in rice plants, and the maximum content of simetryne was found at one or two days after treatment.
3. Detached leaves were dipped into dilute solution containing simetryne, and the amounts of simetryne found in the test leaves were compared with theoretical amounts translocated from solution. The ratio of these two amounts was postulated as the rate of metabolism of simetryne, which showed no difference among leaf positions of rice plants.
4. It is said that simetryne may move in rice plant along the apoplast system. The upper phytomer units of the rice plants treated with simetryne did not fully developed, and this phenomenon seems to suggest that simetryne phytotoxicity has a close relation with the development degree of phytomer units in rice plants.
