Variation in Frankia strains isolated from Alnus root nodules

Hooker, John E (1987) Variation in Frankia strains isolated from Alnus root nodules. PhD thesis, University of Glasgow.

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Several techniques and media were compared for their effectiveness in the isolation of Frankia from nodules of Alnus. The most successful technique was based on differential filtration and was used further to isolate Frankia from nodules of Alnus growing on different sites in Britain. All isolated strains gave rise to sp- nodules, even when isolated from sites known to contain sp+ nodules. Strains did, however, vary morphologically and in their carbon nutrition. Differences were also shown in the ability of strains to effect symbiotic nitrogen fixation in nitrogen-free culture. Comparisons with crushed nodules and strains from The Netherlands and North America showed that British strains were as effective and in some cases more effective than foreign strains. In homologous associations nodule specific activity remained relatively constant and differences in strain effectivity were mainly due to differences in plant nodule productivity. In heterologous associations differences were due more to changes in nodule specific activity and nodule growth remained relatively constant. Plants that fixed most nitrogen during the growth period were not those with nodules of highest specific activity, The most effective associations were homologous associations which combined good nodule growth with satisfactory specific activity. Strain effectivity and its determinants were shown to be different in A. rubra from different provenances. Nodules from all plants evolved little hydrogen and all demonstrated uptake of hydrogen, probably due to the presence of an efficient uptake hydrogenase, indicating a high relative efficiency. Differences in nodule specific activity were not, therefore, due to differences in relative efficiency. Field observations showed that infection or spread of Frankia seems to be inhibited in some peats. This suggests that soil type may influence the symbiosis. This was confirmed in a glasshouse experiment to examine the effect of soil type, host plant genotype and Frankia inoculum source on the symbiosis. The largest effects were observed between different soils; in peat growth was particularly poor and many plants failed to nodulate at all. Differences in growth were also observed with different Frankia sources and host plant genotype and interactions were evident between all 3 factors. Further experiments with aqueous extracts from soils and Frankia in vitro showed that although extracts from mineral soils were always stimulatory, peat extracts could be either inhibitory or stimulatory. Evidence was obtained which suggests that some strains may be adapted to peat sites. The prospects for field inoculation of Alnus rubra with selected strains was examined. Glasshouse experiments to determine competition between indigenous sp+ strains and introduced sp" strains suggest that the introduced Frankia competed successfully for infection of new A. rubra roots with strains already present in the soil. In a further experiment the benefits of inoculation with selected Frankia in the nursery were clearly shown. Although differences in nodule specific activity were similar to those shown under combined nitrogen-free conditions the relative order of effectivity was changed due to soil effects on infectivity and nodule growth. It is clear that, as with the Rhizobium symbiosis, further efforts to isolate and identify Frankia strains which are capable of high rates of symbiotic nitrogen fixation and which show adaptation to particular environmental conditions should result in better prospects for improved tree growth.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Botany
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-76648
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 13:58
Last Modified: 19 Nov 2019 13:58

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