島根県下に於ける秋落の様相(第1報)

Every year, cultivation of rice plant is suffering severe damage from the Akiochi phenomenon.
The diseased spot of Helminthosporiose of the rice plant was observed in the Akiochi region in Shimane Prefecture and these spots were divided into four types. It was suggested that there might exist some correlation between the type of diseased spots and growing conditions.
Spectrographic analysis has been made to clarify the difference of mineral elements in the diseased spots and in the healthy parts of rice plant leaves grown in sound areas and the Akiochi region. Some characteristic in the contents of mineral elements was observed.
In the Akiochi region, the contents of Al, Ca, Si, and Mn increased. Norin No. 37, a suitable variety for Akiochi region, showed little difference in mineral elements between the Akiochi and sound areas but Mihonishiki showed rather striking difference between them. This seem to mean that Norin No. 37 is less affected by the influence of cultivated soil than Mihonishiki.
Generally speraking, the contents of the mineral elements decreased along the following order.
Healthy parts of the Akiochi region, diseased parts of Akiochi region, healthy parts of sound region.
The difference in mineral contents between the diseased spots and healthy parts is not so striking as in potato late-blight.
Until now, it was said that the rice plant cultivated in Akiochi region has less Mn content than that in ordinary paddy fields; but in our experiments, we find the rice plant grown in the Akiochi region has much more Mn content as well as other mineral content than in the ordinary plants. In our experiments, we used the material of diseaed spots and healthy parts seperatly, instead of using the whole plant as had been done in the past.
We find that in Norin No. 37, the ressistant variety to Akiochi, has much more Mn content than Mihonishiki. This tendency coincides with the results of other research workers.