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Published in Crop Sci 21:758-761 (1981)
© 1981 Crop Science Society of America
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Nitrogen Fixation in the Rhizosphere of Cultivated and Wild Rice Strains1

Y. Sano, T. Fujii, S. Iyama, Y. Hirota and K. Komagata2

A modified assay system using the acetylene reduction technique was devised in order to measure large numbers of plants easily, to look into variations among genotypes for N2 fixation in the rhizosphere of paddy rice (Oryza sativa L.), this assay system showed that the activity could be detected immedidately after incubation and the amount of ethylene produced increased linearly with time. It was considered that rice roots were essential for the activity of heterotrophic bacteria contributing N2 fixation in paddy rice. The highest activity was found at flowering stage though large diurnal fluctuation was observed. The differences in nitrogenase activity among rice species and strains were highly significant. In comparisons between cultivated and wild rice strains, cultivated strains generally showed higher activities than wild relatives. These results suggested that the association between rice plants and N2-fixing bacteria was controlled by the genotypes of the plants, and the association might have been enhanced in the course of domestication.

Key Words: Acetylene reduction • Nitrogenase activity • Rhizosphere • Oryza sativa L. • Oryza glaberrima Steud. • Oryza perennis Moench. • Oryza punctata Kotschy ex Steud.

1 Contribution from National Institute of Genetics, Misima, Japan, No. 1347. This research was supported by grant 111905 from the Ministry of Education, Japan.

2 Research scientist; laboratory head; laboratory head; head of Dep. of Microbial Genetics; respectively, National Institute of Genetics, Misima, 411 Japan; and professor, Institute of Applied Microbiology, Tokyo Univ., Tokyo, 113 Japan.

Received for publication May 1, 1980.




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