Abstract:
Inoculation of grain legumes with rhizobia has been recorded to have
a great potential in maximizing biological N2
fixation in these crops. Glycine max
(soybean) is one of the most important grain legumes in the rain fed farming
systems in dry and intermediate zones of Sri Lanka. Rhizobia of wild non-edible
legumes have higher tolerance to prevailing adverse conditions. The main
objective of the current study was to test the ability of certain rhizobial isolates
from wild legumes which could overcome competition by indigenous strains and
effectively nodulate G. max in order to use them as rhizobial inoculants. Rhizobial
strains from wild legumes (C10, M5, VD1, and VW2) which were previously
selected as effective were used in all experiments. Physiological and biochemical
characterization of rhizobia was done by assessing their growth in media with
different pHs (5, 7 and 9), salt concentrations (0.5%, 1%, and 2%) and sugars
(Lactose, Sucrose and Maltose). A field test was conducted with the above four
strains, using a Randomized Complete Block Design (RCBD) with three
replicate blocks per treatment. Seeds were mixed with coir based inoculants
prior to sowing. Three plants from each plot were harvested after 8 weeks and a
nodule count was taken. These plants were oven dried and weighed. Yield and
yield component data were recorded in the remaining plants. C10, M5 and VW2
grew at basic pHs. All the strains showed moderate tolerance to salinity except
M5 which showed a high tolerance to 0.5% and 1% NaCl. VW2 showed a higher
ability to use all carbohydrates while M5 showed moderate ability. Inoculation
with all four strains showed increases in nodulation compared to the
uninoculated N+ and N- controls. Dry matter production with C10, VD1 and
VW2 were significantly higher which was similar to the N fertilizer application.
The highest Average Number of Pods was observed with VD1. Strain C10 gave
the highest value for number of seeds per pod which is significantly higher than
the other treatments. With respect to 100 seed weight strains C10 and VD1 gave
significantly higher values than the uninoculated controls. All the inoculated
treatments gave higher values for seed yield than the uninoculated treatments
whereas strains C10 and VD1 gave significantly higher values. Strains C10, VD1
and VW2 appear to be capable of overcoming competition by indigenous
rhizobia and suitable to be used as inoculants for G. max
