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

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Title Gamma irradiation and autoclave sterilization of peat and compost as the carrier for rhizobial
inoculant production
Author Panlada Tittabutr 1 , Kamonluck Teamthisong 2 , Neung Teaumroong 1 &
Poster Board Number 24
Nantakorn Boonkerd 1
1 School of Biotechnology, Suranaree University of Technology, Nakhon Ratchasima 30000,
Thailand
2 The Center for Scientific and Technological Equipment, Suranaree University of
Technology, Nakhon Ratchasima 30000, Thailand
Although several alternative carriers have been investigated and successfully used instead of peat, the main
problem found in rhizobial inoculant production is contamination by other bacteria or molds that cause reduction
of rhizobial cell number. This study aimed to elucidates the efficient sterilization process of two carriers, peat
and compost before using as rhizobial inoculant. Peat and compost could be efficiently sterilized by irradiation.
The carrier with 10% moisture content could be sterilized by irradiation at 10 kGy, while carrier with 30%
moisture content must be sterilized by irradiation at 25 kGy. Penetration of irradiation through polypropylene (PP)
bag tend to be better than polyethylene (PE) bag, since lower dose of irradiation was needed for carrier
sterilization. However, PE bag appear to be more durable than PP bag after gamma irradiation at high doses.
Nevertheless, contaminants could be detected in irradiated carrier after storage at room temperature for two
months. Thus, autoclaving with tyndallization approach was applied in order to minimize the contaminant
microorganisms in the carrier. Carriers with 10% moisture were autoclaved two times in a row at 121ºC for 60
min, with the waiting period during each time after autoclaving for 18 h could eliminate the fungal contaminants,
while bacterial contaminants still remained about 10 2 cfu/g carrier. The number of Bradyrhizobium sp. PRC008
was in the range of 10 8 -10 9 cfu/g in both irradiated and autoclaved peat after 6 months storage. However, the
numbers of bradyrhizobial cell were reduced in compost sterilized by both methods after one month storage.
These results indicated that carrier material had an important influence on inoculant quality, while sterilization
processes using gamma irradiation and autoclaving with tyndallization approach could be used for efficient
rhizobial inoculant production with peat based carrier.
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2011