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Growth, infectivity and nodulating abilities of some winged bean rhizobia in acid conditions

Shamsuddin, Zulkifli Haji (1987) Growth, infectivity and nodulating abilities of some winged bean rhizobia in acid conditions. PhD thesis, Murdoch University.

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The present research project was undertaken to study the growth of winged bean and its rhizobia, the infectivity and nodulating abilities of winged bean rhizobia, and the symbiotic growth of winged bean, in acid conditions. The effects of different carbon and nitrogen sources and the rhizosphere on growth of rhizobia and final pH of media were also investigated.

Three winged bean cultivars behaved similarly in the response of their top dry matter to soil treatments which increased acidity: they differed in their root responses.

Fifty-two Bradyrhizobium strains from nine international research centres were found to nodulate winged bean and their effectiveness assessed. Forty-one effective strains were screened for growth in acid conditions, using two different techniques.

In soils without plant roots, CB756 began to show a lag phase but could grow at pH 4.4 (1:5 in 0.01 M CaCl2); NRll 2 produced no growth even at pH 4.6. The presence of winged bean roots reduced the rhizobial growth limitations due to the combined effects of low pH (4.4) and addition of aluminium (0.33 -1 cmol (+) kg-1 soil).

The combined effect of low pH (4.4) and aluminium -1 application (0.33 cmol (+)kg-1 soil) reduced nodulation and total nitrogenase activity in winged bean cv. TPtl inoculated with CB756. For NRll, which is unable to grow in acid soil at pH 4.6, a similar reduction occurred at the higher pH (4.6), a trend which directly reflects the influence of survival of rhizobia on nodule number and dry weight, and nitrogenase activity. Growth of TPtl, a cultivar tolerant of acid soil at pH 4.4 when supplied with inorganic nitrogen, was reduced at pH 4.4 and 4.6, when inoculated with CB756 and NRll, respectively.

These results suggest that in the winged bean -Bradyrhizobium symbiosis under acid conditions, the growth of rhizobia and the processes of nodulation and nitrogen fixation are both limited by low pH; these limitations are greater than that on growth of the host-plant. The limitations to nodulation and total nitrogen fixed vary inversely with the acid tolerance of the rhizobia. Acid-tolerant strains formed nodules earlier and fixed nitrogen sooner than acid-intolerant strains.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Loneragan, Jack and Dilworth, Michael
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