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Physiology and Biochemistry

Tobacco Ringspot Virus and Rhizobium Interactions in Soybean: Impairment of Leghemoglobin Accumulation and Nitrogen Fixation. R. G. Orellana, Research Plant Pathologist, Applied Plant Pathology Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; F. Fan(2), and C. Sloger(3). (2)Support Plant Pathologist, Applied Plant Pathology Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; (3)Research Plant Physiologist, Cell Culture and Nitrogen Fixation Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 68:577-582. Accepted for publication 24 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-577.

Tobacco ringspot virus (TRSV)-infected and noninfected Harosoy soybeans grown in the greenhouse with Rhizobium japonicum-110 seed-inoculant were studied during prebloom, bloom and seed-set, bloom and early pod, pod-fill, and mature-pod stages. The effects of the disease relative to noninfected plants were the following: (i) the virus significantly reduced top, root, and nodule growth; (ii) nodulation and hence symbiotic activity were nearly or completely suppressed until the plants were about 40 days old and were in the bloom and early pod stage; (iii) after nodulation started, nodule fresh weights were reduced 85, 67, and 67% during the last three growth stages; (iv) leghemoglobin (LH) content decreased 3% during the bloom and early pod stage but increased 33 and 25% during the successive pod-fill and mature-pod stages, respectively; (v) N2-fixation rates calculated in micromoles of C2H4 gram-nodule1 hr1 (on a fresh-weight basis) were increased 30, 99, and 57%, respectively, during the last three growth stages as the plants aged; however, N2-fixation rates, calculated on plant basis for the last three growth stages, decreased 81, 41, and 23%; and (vi) TRSV-infected plants remained green 2-3 wk longer than the noninfected controls. Correlation coefficients between LH accumulation and N2 fixation rate for TRSV-infected and noninfected plants were r = 0.9900 and 0.8905, respectively. These results demonstrate that soybean budblight disease severely delays nodulation and interferes with the efficiency of the N2-fixation process. The delayed, although increased, specific activity of TRSV-infected nodules would be too late to promote yield.