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Research Articles
ScienceAsia 33 (2007): 069-077 |doi: 10.2306/scienceasia1513-1874.2007.33.069
Growth, Survival and Field Performance of
Bradyrhizobial Liquid Inoculant Formulations with
Polymeric Additives
Panlada Tittabutra, Waraporn Payakaponga, Neung Teaumroonga, Paul W. Singletonb, and
Nantakorn Boonkerda*
ABSTRACT: Liquid inoculant has become a preferred method for inoculating legumes with bradyrhizobia. Finely
ground peat has been the standard of quality for inoculants for many years. Suitable peat for an inoculant
carrier is difficult to find and limited in supply in many locations. We evaluated six different polymeric
additives (polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), polyvinyl alcohol (PVA), gum arabic,
cassava starch, and sodium alginate) for their ability to support growth and promote survival of several
strains of bradyrhizobia and rhizobia during storage. Some concentrations of various additives to yeast
extract mannitol (YEM) media promoted higher cell density compared to cells cultured in YEM media alone.
There was a large interaction between strains of rhizobia and the additives in relation to cell survival. Shelflife
of liquid inoculant formulations depended on the strain of rhizobia and additives, when stored at room
temperature. Liquid inoculants formulated with sodium alginate promoted long-term survival of all rhizobial
strains, but its effect on cell survival was not as great as peat. Peat also provided the greatest protection to
cells of bradyrhizobia after application to the seed surface followed by incubation at 40°C. Survival of
bradyrhizobia was maintained at 105 cells/seed after 48 hours of incubation. Liquid inoculant formulated
with gum arabic, sodium alginate, PVP, or cassava starch supported survival at only 104-105 cells/seed, while
PEG and PVA additives performed poorly and cell numbers fell to 103 cells/seed at 48 hours after inoculation.
One-week old liquid inoculants with bradyrhizobia were tested for their ability to nodulate and fix nitrogen
under field conditions. We found that liquid inoculant performance was as good as that of peat based
inoculant.
KEYWORDS: additive, bradyrhizobia, liquid inoculant, polymeric substance, survival.
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a School of Biotechnology, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
b Department of Tropical Plant and Soil Sciences, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
* Corresponding author, E-mail: nantakon@sut.ac.th
Received 13 Sep 2005,
Accepted 5 Jul 2006
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