Isolation of Antagonistic Organisms against Rigidoporus microporus from Soils of Main Rubber Growing Areas in Sri Lanka
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Date
2013
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Journal ISSN
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
White root disease is the most destructive root disease in Sri Lankan rubber plantations. It is
caused by the fungal pathogen Rigidoporus microporus which spreads through infected roots
and mycelial aggregates (rhizomorphs) through the soil (Jayasinghe et al., 2010). Soil characters
are important for the disease progress. Soil microorganisms may reflect changes in soil quality
since the dynamics of their populations describe the status and trends of soil conditions (Lu et
al., 2012). Soil habited micro-organisms play a critical role in rubber plantations, for example in
biological control of soil borne fungal diseases. Present study was carried out to isolate the
potential antagonistic micro-organisms from different rubber growing soils, against Rigidoporus
microporus the causative agent of white root disease in Sri Lanka.
Methodology
Isolation of the pathogen was under taken from rubber (Hevea brasiliensis) roots after
sterilization using 0.01% Hg2Cl2 for 2 minutes. The resulted fungal culture was maintained on
Malt Extract Agar (MEA). Microorganisms were isolated from twelve soil samples collected
from main rubber growing districts in Sri Lanka viz, Kaluthara, Rathnapura, Kegalle and
Monaragala. Chemical properties of the soil such as pH, organic matter content and moisture
content of each sample were measured. Dilution plate technique was used to isolate the
microorganisms in Potato Dextrose Agar medium (PDA). The dishes were then incubated with
three replicates and colony forming units were counted after 4 days. Direct opposition method
was used for isolating the potential antagonistic microorganisms against the pathogen in the
MEA medium for six days. Selected antagonistic fungi were introduced onto PDA media and
bacteria were cultured in nutrient agar (NA) while actinomycetes were grown in starch-casine
agar. Growth inhibition of the pathogen’s colony was measured the presence of different
antagonistic microorganisms using dual culture plates to investigate the most promising
antagonistic organisms that would be useful in controlling the growth of R. microporus. The
variation of soil properties and microbial populations among sites and districts were analyzed by
Nested ANOVA procedure by using SAS (SAS Institute Inc., 2009) software programme. The
growth inhibition of pathogen was analyzed with analysis of variance (ANOVA) procedure of
SAS (SAS Institute Inc., 2009). Significant means of treatments were separated using the Least
Significant Difference (p<0.05) test (LSD).
Results and Discussion
Fungi and bacteria were isolated from the four rubber growing districts under investigation. The
results demonstrated that both the antagonistic fungi and bacteria effective against R.
microporus are available in the soils of rubber plantations in Sri Lanka. The distribution varied
with the agro-climatic region and the environmental conditions. The number of bacterial
colonies was more compared to the fungal colonies (Table 1). Among the micro-organisms
isolated 11 bacteria ssp. and 20 fungi were effective based on the mean growth inhibition (Plate
1 a and b). Variation of growth inhibition of the pathogen by different antagonistic organisms
was significantly different (p<0.05) at 95% confidence level (α = 0.05).
Description
Keywords
Agriculture, Export Agriculture, Crop Production, Rubber, Rubber Plantations