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The Relation of Soil Temperature to Germination of Certain Philippine Upland and Low-Land Varieties of Rice and Infection by the Helminthosporium Disease

Gerardo Offimaria Ocfemia
American Journal of Botany
Vol. 11, No. 7 (Jul., 1924), pp. 437-460
Stable URL: http://www.jstor.org/stable/2435585
Page Count: 28
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Relation of Soil Temperature to Germination of Certain Philippine Upland and Low-Land Varieties of Rice and Infection by the Helminthosporium Disease
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Abstract

The results of the experiments discussed in the foregoing pages may be summarized as follows: 1. Experiments conducted to determine the effect of soil temperatures from 16⚬ to 40⚬ C., with soil moisture varying from 16 to 100 percent of the water-holding capacity, upon the germination of rice, showed that emergence occurred in from 1 to 4 days at 36⚬ C. and 32⚬ C., in from 4 to 7 days at 28⚬ C., in from 5 to 9 days at 24⚬ C., in from 2 to 6 days at 40⚬, in from 6 to 13 days at 20⚬ C., and in from 9 to 16 days at 16⚬ C. It was also found that sterilizing the soil for a long time under high steam pressure did not produce much effect upon the rate of germination or the time of emergence. The quality of the seed affects the percentage of germination at soil temperatures from 16⚬ to 24⚬ C. Above this soil temperature, the influence of seed-borne parasites becomes less effective. 2. Inoculation experiments with H. oryzae on rice demonstrate that seedlings are infected at soil temperatures from 16⚬ to 36⚬ C. The development of the lesions on the aerial parts of the rice is much faster from 28⚬ to 32⚬ C., because of the rapid growth of the fungus and of rice seedlings at these temperatures. Severe blighting of seedlings before emergence occurs at 16⚬ to 24⚬ C. At 36⚬ C. the percentage of infection is low and the growth of the lesions is comparatively slow. 3. The temperatures favorable for the growth and sporulation of H. oryzae and for the growth of Philippine varieties of rice are nearly the same. The development of the lesions is most rapid at temperatures at which the subsequent growth of the rice is best. A more severe infection, resulting in blighting of the seedlings before emergence, occurs at soil temperatures from 16⚬ to 24⚬ C. At 36⚬ C., only an occasional blighting of the seedlings occurs. Planting rice in soil or in seed beds with temperatures of from 32⚬. to 36⚬ C. will materially reduce infection and blighting by H. oryzae. 4. Although the coleoptile, mesocotyl, and seedling-root infections are more abundant and the lesions develop faster at higher soil temperatures, they are less harmful and are finally outgrown by the rice seedlings. 5. At lower soil temperatures, even coleoptile, mesocotyl, and seedlingroot infections are conducive to blighting after the seedlings have emerged through the soil.

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