IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Wednesday 30 November 2011
Concurrent Session 12 – PGPR & Plant Production
1100 – 1230
Authors: Sharon Fox 1 , Graham O‟Hara 1 and Lambert Bräu 1
1 Centre for Rhizobium Studies, Murdoch University, Murdoch, 6150, Western Australia.
Presentation Title: Differential effects of Pseudomonas fluorescens WSM3457 on enhanced
Medicago nodulation
Presentation Time: 1100 - 1120
Pseudomonas fluorescens WSM3457 has been studied as a nodulation increasing bacteria (NIB) since 2006
due to increases in the nodulation of subterranean clover reported in glasshouse and field trials. We have
demonstrated a similar phenomenon on the Medicago truncatula / Sinorhizobium medicae WSM419 symbiosis.
During glasshouse trials it was observed that co-inoculation results in larger, pinker nodules, located higher on
the root system, compared to M. truncatula inoculated with only S. medicae WSM419.
Nodule location suggested that nodules were elicited earlier on co-inoculated plants and this was confirmed
during studies comparing the rate of nodule initiation on M. truncatula inoculated with either S. medicae WSM419
or both WSM419 and P. fluorescens WSM3457. The results also demonstrated that there was a significant
increase in symbiotic effectiveness, both in terms of plant mass and total fixed N.
Following those results it was investigated whether co-inoculation increased the effectiveness of a partially
effective symbioisis, namely that of the symbiosis between S. meliloti 1021 with M. truncatula. The results show
that there was no significant increase in shoot mass with co-inoculation with P. fluorescens WSM3457. However,
the nodulation data tells a conflicting story, with enhanced nodulation scores on M. truncatula when P.
fluorescens WSM3457 was co-inoculated with S. meliloti 1021.
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