Dry Matter and Nitrogen Accumulation in Rice Inoculated with a Nitrogenase-Derepressed Mutant of Anabaena variabilis
- Freeman Kamuru,
- Stephan L. Albrecht,
- Leon H. Allen and
- K. T. Shanmugam
- D ep. of Agronomy, Agronomy Physiology Lab., P.O. Box 110965, Univ. of Florida,, Gainesville, FL 32611-0965
U SDA-ARS, Columbia Plateau Conserv. Res. Ctr., P.O. Box 370, Pendleton, OR 97801
U SDA-ARS, Crop Genetics and Environmental Res. Unit, Agronomy Physiology Lab., P.O. Box 110965, Univ. of Florida,, Gainesville, FL 32611-0965
D ep. of Microbiology and Cell Science, P.O. Box 110700, Univ. of Florida, Gainesville, FL 32611-0700
Cyanobacteria contribute to the N economy of flooded rice (Oryza sativa L.) fields by reducing N2 to NH3. The purpose was to determine the extent to which a nitrogenase-derepressed mutant strain of the cyanobacterium Anabaena variabilis (strain SA-1), capable of excreting newly fixed N as NH3, could provide N for rice plants grown outdoors in pots. Growth of plants inoculated with the mutant strain was compared with growth of plants inoculated with the parent strain (A. variabilis, strain SA-0) or fertilized with inorganic N fertilizer [(NH4)2SO4] at rates of 0 (control), 25, 50, and 100 kg N ha−1. Rice plants inoculated with the mutant cyanobacterium produced more panicles than plants inoculated with the parent strain. Dry matter and total N contents of the root, shoot, and grain were significantly greater (P < 0.05) in the plants inoculated with the NH3-excreting mutant strain than plants that were inoculated with the parent strain of the cyanobacterium. Under these conditions, the contribution of the mutant cyanobacterium to growth and yield of rice plants was equivalent to the application of 71 to 73 kg N ha−1 as (NH4)2SO4. Estimates the rate of N2-fixation (acetylene reduction) in pots inoculated with the NH3-excreting mutant cyanobacterium were about twice the amount observed in pots inoculated with the wild-type strain, even in the presence of (NH4)2SO4. Pots inoculated with the mutant strain also had more NH3 in the flood water than pots that were inoculated with the parent strain. The NH3-excreting strain of A. variabilis shows potential for development for use as a biofertilizer in paddy rice production in areas where inorganic fertilizer N is unavailable or expensive and in rice production systems that aim to minimize environmental pollution from inorganic N fertilizers.
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