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 13 - Inoculant Quality & Application
1600 - 1740
Authors: Rosalind Deaker, Andrea Casteriano, Elizabeth Hartley and Greg Gemell
University of Sydney, Australia
Presentation Title: Making the most of high quality inoculants: survival of rhizobia during application to
legume crops
Presentation Time: 1600 – 1620
Despite developments in inoculant technology and a high level of compliance of commercial legume inoculants
to quality standards, poor survival of rhizobia during delivery to legume crops and pastures is still a major issue.
Loss of viability of inoculant microorganisms limits the potential for maximum nodulation by elite strains and thus
nitrogen fixation and yield. Legume inoculants are most commonly applied to seed prior to sowing; however, the
seed surface presents a hostile environment for rhizobia exposing cells to desiccation stress and potentially toxic
chemicals. Inoculant technology balances an incomplete scientific understanding of growth and survival with
production and market demands. As a result, the potential for rhizobia to survive seed coating operations both
commercially and on farm is not maximised.
Polymer adhesives are typically used to fasten inoculants, growth enhancing and pelleting materials to seed.
However, polymer properties that enhance survival of inoculant microorganisms are poorly defined. Preference
for polymer latexes in the pre-inoculated seed industry is largely based on pellet quality and ease of handling but
little attention has been given to compatibility and protection of rhizobia. Polymer latexes are not only likely to
contain incompatible chemical constituents such as excess polymerisation initiator, surfactants and biocides but
are also faster drying than solution polymers. Rhizobial survival is substantially improved when the rate of
dehydration is reduced.
In addition to external protectants, intracellular physiological changes after growth of rhizobia in different media
prior to drying significantly affect survival and may be responsible for improved desiccation tolerance. A better
understanding of how to induce physiological mechanisms involved in desiccation tolerance will provide new
direction for inoculant technology development. It is expected that combining targeted physiological conditioning
during production of inoculants with optimised external protection during application will maximise the potential of
microbial inoculants to enhance agricultural production systems.
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