Response of Glycine max L. Merr., Vigna unguiculata L. Walp, Phaseolus lunatus L., Phaseolus vulgaris L. to inoculation as influenced by the indigenous Rhizobia
1989
Ortega, M.L.C.
In the pot experiment, soybean and snap bean showed no response to inoculation in terms of dry matter yield and N uptake where the soil had 290 cells/g soil of Bradyrhizobium japonicum and 1.4 X 10 to the fourth power cells/g soil of Rhizobium leguminosarum biovar phaseoli. In the field, where the number of background rhizobia was only 100 cells/g soil, inoculated soybean showed increased nodulation and plant biomass at maturity. Inoculation also increased seed yield of snap bean by 230% in the soil where less than 4 cells of the native snap bean rhizobia per gram soil was detected. Cowpea and lima bean were not influenced by inoculation in terms of the parameters tested, both in the pot and field experiments. Native population of rhizobia for both crops were found to be 5.2 x 10 to the fourth power and 1.28-8.0 x 10 to the second power cells/g, respectively. The plant infection method of determining rhizobia compared well with plate count when the test plant was soybean, but it underestimated rhizobial counts for Phaseolus species by tenfold and for Macroptilium atropurpureum by hundredfold. Eighty-five percent and 70% of native soybean and cowpea rhizobia, respectively were as effective as the inoculum-strains. None of the native rhizobia isolated was related to the inoculum strains on the basis of serological reactions. Results of the present study showed that the number of native rhizobia is a determining factor in inoculation response. It seems that no response to inoculation may be expected when the native rhizobia exceed 100 cells/g soil.
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