Browsing by Author "Fernando, T.H.P.S."

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    Antagonistic Effect of Five Native Trichoderma Isolates on Economically Important Foliar Pathogens of Rubber
    (Uva Wellassa University of Sri Lanka, 2016) Sandamali, P.K.N.N.; Chandrasena, G.; Fernando, T.H.P.S.; Silva, P.D.P.M.D.
    Rubber foliar diseases play an important role in latex yield losses of rubber plantations in Sri Lanka. The frequent use of chemical fungicides to control causative pathogens leads to environmental pollution, hazardous to human and may lead to the development of new chemical resist pathogenic strains. Trichoderma species are the most widely studied bio control agent against many economically important plant pathogens. Hence, an attempt was made to investigate the antagonistic effect of five native Trichoderma strains on the plant pathogenic fungi; Colletotrichum spp., Corynespora cassiicola, Phytophthora spp. and Drechslera heveae. Foliar pathogens were isolated, identified and confirmed based on the symptoms, cultural and reproductive characteristics. Five Trichoderma strains isolated from different rubber growing soils in Sri Lanka were tested in vitro for their antagonistic effects against four foliar pathogens. The results obtained from dual culture tests showed that all five Trichoderma isolates effectively checked the growth of the four foliar pathogens. The test antagonists grew faster than the pathogen limiting their growth. Trichoderma isolate A was the best antagonist against Drechslera heveae, Corynespora cassiicola and Colletotrichum spp. showing percentage inhibition of 75.63 %, 51.34 % and 74.46 % respectively. Isolate B showed the best inhibition rate (70.99 %) against Phytophthora spp. All antagonists showed their lowest inhibition rates against Drechslera heveae. All the tested Trichoderma isolates showed antagonistic effects against four foliar pathogens under investigation. Therefore, the fungal strains can be used for further greenhouse and field studies to confirm the feasibility of using for the management of rubber foliar pathogens. Key Words: Trichoderma spp., Drechslera heveae, Corynespora cassiicola, Colletotrichuin spp., Phytophthora spp.
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    Isolation of Antagonistic Organisms against Rigidoporus microporus from Soils of Main Rubber Growing Areas in Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2013) Jayamuthu, J.P.D.L.; Herath, H.M.S.K.; Fernando, T.H.P.S.; Siriwardena, D.
    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).
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    Variability of Corynespora cassiicola Isolates from Non-Traditional Rubber Growing Areas
    (Uva Wellassa University of Sri Lanka, 2013) Udayasiri, G.R.P.N.; Chandrasena, G.; Fernando, T.H.P.S.; Nishantha, N.A.D.
    Corynespora leaf fall disease (CLFD) caused by Corynespora cassiicola (Berk and Curt) is the most distructive foliar disease reported in Sri Lanka and it has become a serious threat to the world natural rubber industry (Fernando et al., 2012). CLFD was first detected in Sri Lanka during the year 1985 and the first epidemic was experienced in 1985-1986, devastating the clone RRIC 103, one of the most prestigious genetic materials bred by Sri Lankan scientists. Very recently, a leaf spot disease with uncommon symptoms was reported from non- traditional rubber growing areas. The disease samples were collected from the field plants of RRIC 121 and the isolation of the samples consistently resulted Corynespora cassiicola isolates. The objective of this investigation was to report the newly recorded disease symptoms, isolate the pathogen and also to study the variability in cultural and reproductive characteristics. Methodology Diseased leaf samples were collected from the several traditional and non- traditional rubber growing areas and the different symptoms were recorded. Five isolates were collected, purified and single conidia cultures were raised on to potato dextrose agar (PDA). Mycelial plug (5.0 mm) from the advancing margin of a seven-day old culture of the test isolates and were placed at the centre of Petri plates containing PDA. The plates were incubated at RT under normal light and dark regimes. Colony colour, texture and the growth were recorded after 8 days of incubation period. The growth was also recorded. The cultural characteristics in different culture media were also observed. Ten-day old cultures of the isolates grown on PDA were used to prepare conidia suspensions. Reproductive characteristics were evaluated by using slide cultures, conidia shapes and their sizes. The conidial concentration of the filtrates was measured using a haemocytometer. Pathogenicity of the isolates was tested a concentration of 2×10 conidia/ ml) were used for artificial inoculations. Apple green leaves of the clone, RRIC121 clone were used for pathogenicity tests. Toxin production was evaluated by using leaf wilt bio assay and leaf puncture bio assay.