Tobacco Ringspot Virus and Rhizobium Interactions in Soybean: Impairment of Leghemoglobin Accumulation and Nitrogen Fixation

ORELLANA, R. G., F. FAN, and C. SLOGER. 1978. Tobacco ringspot virus and Rhizobium interactions in soybean: impairment of leghemoglobin accumulation and nitrogen fixation. Phytopathology 68: 577-582. Tobacco ringspot virus (TRSV)-infected and noninfected N2-fixation rates calculated in micromoles of C2H 4 " gramHarosoy soybeans grown in the greenhouse with Rhizobium nodule-l' hr1 (on a fresh-weight basis) were increased 30, 99, japonicum-1 10 seed-inoculant were studied during and 57%, respectively, during the last three growth stages as prebloom, bloom and seed-set, bloom and early pod, pod-fill, the plants aged; however, N2-fixation rates, calculated on and mature-pod stages. The effects of the disease relative to plant basis for the last three growth stages, decreased 81, 41, noninfected plants were the following: (i) the virus and 23%; and (vi) TRSV-infected plants remained green 2-3 significantly reduced top, root, and nodule growth; (ii) wk longer than the noninfected controls. Correlation nodulation and hence symbiotic activity were nearly or coefficients between LH accumulation and N2 fixation rate completely suppressed until the plants were about 40 days old for TRSV-infected and noninfected plants were r = -0.9900 and were in the bloom and early pod stage; (iii) after and -0.8905, respectively. These results demonstrate that nodulation started, nodule fresh weights were reduced 85, 67, soybean budblight disease severely delays nodulation and and 67% during the last three growth stages; (iv) interferes with the efficiency of the N2-fixation process. The leghemoglobin (LH) content decreased 3% during the bloom delayed, although increased, specific activity of TRSVand early pod stage but increased 33 and 25% during the infected nodules would be too late to promote yield. successive pod-fill and mature-pod stages, respectively; (v) Bud blight of soybean [Glycine max (L.) Merr.], which that interact with Rhizobium japonicum (Kirchn.) is caused by the seedborne and sap-transmitted tobacco Buchanan has been, with a few exceptions (7, 15, 16, 20, ringspot virus (TRSV), is a widely distributed, prevalent, 21), very limited. Studies of the interaction of soybean and yield-reducing disease of this crop and of other viruses and R.japonicum have dealt mainly with soybean leguminous plants (1, 10). Recently, we characterized mosaic virus (SMV) as it affects nodulation and total TRSV in soybean roots and in root nodules of plants nitrogen content (21) and nodule infection (20). Similar grown from TRSV-infected seed as well as from research also has been reported on the Arhar mosaic of artificially inoculated plants (7). Tobacco ringspot virus pigeon peas (18), enation mosaic of Dolichos (17), and also has been detected in meristematic tissue of root tips other bean mosaics. We recently reported briefly on the and in the inner root cap of bean (Phaseolus vulgaris) (5). effects of TRSV on N2 fixation in soybeans (14). In the United States the importance of this disease Leghemoglobin (LH), the heme protein complex, is varies with the amount of TRSV-infected seed planted likely to function in the symbiotic fixation process by and the subsequent dispersal of the virus. In continental facilitating diffusion and regulation of 02 for the China, the center for soybean domestication and source respiration of the nitrogenase-containing Rhizobium of several wild species of Glycine, budblight ranks with bacteroids in the nodule (4, 6, 8, 24). Myoglobin has a soybean mosaic and soybean stunt as one of the three similar function in the regulation of pO2 in mammalian most important virus diseases of soybeans (19); it also is muscle cells (23, 24). In leguminous plants it has been present in other countries, shown that LH biosynthesis coincides with the onset of Research conducted thus far on diseases of soybean the symbiotic process in the young plant (3, 8, 23). It is 00032-949X/78/000 096$03.00/0 apparent, however, that such an association becomes less Copyright @ 1978 The American Phytopathological Society, 3340 pronounced as the plant ages. Pilot Knob Road, St. Paul, MN 55121. All rights reserved. We now present additional data on soybean infection