4. Discussion
The use of biofertilizers or plant growth stimulating bacteria in
agricultural fields has been limited by saline soil environments, as
salinity has an adverse effect on them (Ibekwe et al., 2009).
Therefore, tolerance to salinity is an important requirement that
enables their use in saline soil conditions. Our results in Fig.1 were
in agreement with our previous study, in that PNSB grew better in
microaerobic light than in aerobic dark conditions (Panwichian
et al., 2010). Hence, only 45 isolates were selected for further
screening to choose the most promising strains for use in saline
paddy fields and the two PNSB strains (TN114, PP803) were
selected based on their release of extracellular ALA and ability to
reduce CH4 emissions. The optimal concentration of 0.25% NaCl for
both PNSB strains (Fig. 2) was close to the average salt
concentrations in the original habitats: paddy fields with EC
3.00–4.00 mS cm1 (Nunkaew et al., 2012). Apparently the strains
have adapted or been selected for this level of salt. It is of interest,
that they were able to grow at higher concentrations up to 6% NaCl