Enhancement of tolerance to high salinity and extreme pH conditions in common bean (phaseolus vulgaris L.)-nodulating rhizobial isolates from hararghe lowlands and mid altitudes, eastern ethiopia, through physical and chemical mutagenesis

Enhancement of tolerance to high salinity and extreme pH conditions in common bean (phaseolus vulgaris L.)-nodulating rhizobial isolates from hararghe lowlands and mid altitudes, eastern ethiopia, through physical and chemical mutagenesis

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Title: Enhancement of tolerance to high salinity and extreme pH conditions in common bean (phaseolus vulgaris L.)-nodulating rhizobial isolates from hararghe lowlands and mid altitudes, eastern ethiopia, through physical and chemical mutagenesis
Author: Mulugeta, Mekonnen; Kebede, Dr Ameha
Abstract: The intent of this study was to examine the effectiveness of chemical and physical mutagenesis on enhancement of tolerance of common bean (Phaseolus vulgaris L.) nodulating rhizobial isolates from Hararghe lowlands and mid altitudes to extreme salinity and pH conditions. A total of 50 isolates were obtained from soil samples of three weredas in Hararghe lowlands and mid altitudes using the host trap method and were presumptively identified as rhizobia. Among the five highly effective wild isolates except HUCR 3D showed significantly (p <0.05) higher nodule number than both positive and negative controls. The physiological tests revealed that among the 50 wild isolates 43(86%), 37(74%), 29(58%), 6(12%), 4(8%), and 2(4%), grew at 2%, 4%, 6%, 8%, 9%, and 10% NaCl concentration, respectively. 50(100%) of the isolates grew in the range of pH 5.5 - 8.5. 2 (4%) and 38(76%) of the isolates were grew at pH 4.5 and pH 5 while 48(96%), 43(86%), 40(80%) and 37(74%) of the isolates were able to grow at pH 9, pH9.5, pH10 and pH 10.5 respectively. After mutagenesis, a total of 8 mutants were selected based on their ability to survive at extreme salt and pH conditions. 100% of the mutants were found to be symbiotically highly effective. The nodule number of mutants were positively and significantly correlated with nodule dry weight (r = 0.85, P < 0.0001) on sand culture. Six of the highly effective mutants were tested on unsterilized soil in controlled growth chamber. The correlation data on soil experiment displayed that nodule number was associated positively and significantly (r = 0.73, p<0.0001) with NDW while SDW was positively correlated with percent N (r = 0.8, p<0.0001) and total nitrogen content (r = 0.9, p<0.0001). Physiological test of mutants also showed that, 5(63%) and 3(36%) of mutants were able to grow at salt concentrations of 11% and 12%, respectively. 3(38%), 4(50%), 2(25%) and 2(13%) of the mutants were able to grow at pH 4, 11, 11.5 and 12 respectively. Among the observed rhizobium isolates, HUCR (3D, 3A), HUCR 2D and HUCRM 2D showed the highest symbiotic effectiveness. Only the mutant isolates HUCRM2D (which tolerated 12% NaCl, pH4, pH12), HUCRM5C (which tolerated 12% NaCl, pH 4, 5 HUCRM3B (which tolerated 12% NaCl) and HUCRM9C (which tolerated 11% NaCl) were grow successfully at extreme conditions. Thus, on the basis of their symbiotic effectiveness and tolerance to extreme environmental conditions, these wild and mutant isolates were recommended to be used as candidates for future development of rhizobial inoculants of common bean grown under saline, extreme temperature and pH conditions.
Description: 89p.
URI: http://hdl.handle.net/123456789/3259
Date: 2013-05


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