Publications

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    U.V.A Buddhika, G.Seneviratne, C.L Abayasekara
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    ABSTRACT: Beneficial microorganisms used as biofertilizers enhance seed germination and vigour through breaking seed dormancy and hormonal effects. However, their higher production of hormones like indole acetic acid (IAA) result low seed germination. Therefore, they need a regulation of the IAA production for increased plant growth. Such control exists in developed fungal-bacterial biofilms (FBBs), fungal surface-attached bacterial communities. Therefore, present study compares two FBBs and their seven bacterial monoculture counterparts for IAA production and seed germination with maize as the test plant. Results showed that two biofilms increased seed germination and vigour significantly compared to the monocultures whereas, relatively low IAA concentrations, which were comparable with lower limit of the monocultures. IAA production of monocultures was related negatively to seedling vigour, confirming that relatively low IAA concentrations are more favorable for seed germination. Thus, results suggested a regulatory mechanism for optimizing IAA concentration, and/or factors other than IAA for plant growth benefits in the case of biofilms. In conclusion, it is clear that the FBBs differ from bacterial monocultures in regulating improved seed germination and plant growth. Consequently, FBBs warrant formulating biofertilizers in the biofilm mode for futuristic agriculture.
    International Journal of Scientific and Research Publications. 01/2014; 4(1):1-5.
  • U.V.A Buddhika, G. Seneviratne, C.L. abayasekara
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    ABSTRACT: Soil biodiversity include living organisms existing in the soil and can be categorized as micro, meso and macro biota interacting with each other forming biological web. Generally, soil biodiversity can be lost and deteriorated due to several biotic and abiotic factors. However, recovering of depleted biodiversity is a serious challenge. In agricultural ecosystems, improved biodiversity has been recorded in the application of developed microbial biofilms. N2 fixing bacteria and rhizosphere fungal species have been used to develop fungal-bacterial biofilms in vitro. When such biofilms are coupled with 50% of recommended chemical fertilizers, they tended to increase soil biodiversity especially bacteria, fungi and cyanobacteria with pest and weed control. Therefore, this review is focused on the biofilms developed in vitro and their impact on the enrichment of soil biodiversity in agriculture. Dormant seeds of plants and microbes, which create voluminous seed bank in the soil, tend to be resuscitated with the induction of beneficial organic secretions of the applied biofilms. Consequently, the dormant seeds, which are physiologically inactive, are transformed into physiologically active forms. Thus, the soils applied with in-vitro developed biofilms can enrich the soil biodiversity, addressing many issues related to loss of biodiversity in agroecosystems.
    National Symposium on Soil Biodiversity 2013, Sri Lanka Institue of Development Administration; 12/2013
  • U.V.A Buddhika
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    ABSTRACT: Use of nitrogen fixing bacteria as biofertilizers for particularly legumes is a common practice and rhizobia have been formulated as biofertilizers for more than a century. As a recent development, N2 fixing bacteria from a wide range of genera have been combined with rhizosphere fungi to form fungal-bacterial biofilms (FBBs). These FBBs can be developed as biofilmed biofertilizers (BFBFs) to be coupled with 50% chemical fertilizers (CF) to achieve comparable yields with 100% CF for several crops. Therefore, the current study was focused to develop an effective BFBF for maize cultivation in Sri Lanka. Microbes were isolated and screened, thereby two BFBFs were developed, and they were compared with their monocultures for biological nitrogen fixation (BNF), seed germination, and seedling vigor and indole acetic acid (IAA) production. Fertilizing potential of the two BFBFs were tested in greenhouse and two farmer fields. Treatments were, 100% CF, 50% CF and 50% CF + BFBF1, 50% CF + BFBF2. One of the two BFBFs was selected and further tested in four fields representing different localities in the maize belt of the country. Effect of the BFBFs on soil quality was tested by evaluating microbial diversity and seed germination. The BFBFs significantly enhanced nitrogenase activity. Further, seedling vigor was increased significantly over the monocultures with a reduced IAA production by both BFBFs, possibly through a regulation of the hormone. The application of 50% CF + BFBFs gave a yield comparable to 100% CF. The 50% CF + BFBFs maintained high soil NH4+ and low PO43- availabilities with significantly high root associated BNF. High photosynthetic activity and chlorophyll content, high diversity of fungi, bacteria and cyanobacteria in the soil-plant system with a significant contribution to soil health were observed with 50% CF + BFBFs compared to 100% CF. Regulation of the IAA production by the BFBFs showed their social communication for improved mutual benefits in their symbiosis, which was not observed in the microbial monocultures. This led to increased microbial diversity, resulting in a healthy soil. Accordingly, BFBFs are not only biofertilizers, but also act as microbial ameliorators, supporting to establish sustainable agroecosystems in maize cultivation. Furthermore, as CF could be reduced by 50% with the use of this BFBF technology, the country could save half the expenses on CF imports, thus contributing immensely to the country’s economy. Since, initial soil total P below 0.06% limited yield potential of the BFBFs over the 100% CF, future research is warranted to formulate improved BFBFs with high acid producing capacity and optimized NPK in CF formulations to be coupled with the BFBFs, in order to maximize the use of BFBFs.
    09/2013, Supervisor: G.Seneviratne, C.L.Abayasekara
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    ABSTRACT: Microorganisms use dormancy as a tactic to evade from unfavourable fluctuations of environment conditions, which results in a voluminous soil seed bank of coexisting species. This has now been well proven with the advent of molecular techniques. Sporadic resuscitation of the dormant microbes contributes to maintain ecosystem functioning. The interchange of dormant and active stages aids vast number of species to coexist whilst maintaining persistent populations amidst constant evolutionary pressure. This interchange is a response to dynamic biotic and abiotic factors in the soil environment. Amongst factors deciding this switch, host factor is well documented in the case of plant-associated microorganisms. In addition to the responsive interchange in the fluctuating environments, a spontaneous interchange takes place in stable environments, which is determined by quorum sensing (QS) that leads to emergence of subpopulations. This is theoretically known as “kin selection” or the promotion of species depending on the degree of genetic relatedness amongst the individual organisms. All in all, those mechanisms have resulted in a lesser number of individuals in active stage, due to ever-increasing adverse conditions imposed on the environment. This has caused to collapse sustainability in many ecosystems. However, recent research shows that if developed beneficial microbial communities in biofilm mode would be introduced to the soil, they can increase the emergence of soil microbial diversity, favouring surfacing of subpopulations of beneficial species. It is now evident that the biofilm actions break dormancy of the microbial seed bank for the increased resuscitation of the dormant cells.
    Plant Microbe Symbiosis- Fundamentals and Advances, Edited by Naveen Kumar Arora, 07/2013: chapter 13.Diversity of plant root associated microbes: its regulation by introduced biofilms: pages 351-372; Springer India., ISBN: 978-81-322-1286-7
  • U.V.A Buddhika, G.Seneviratne, C.L. Abayasekara
    Jaffna University International Research Conference-2012; 07/2012
  • U.V.A Buddhika, G. Seneviratne, C.L. Abayasekara
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    ABSTRACT: Nitrogen fixing microorganisms play a major role in enhancing plant growth and development through biological nitrogen fixation (BNF). Their coupling with a fungal species develops fungalbacterial biofilms, which can be used as biofilmed biofertilizers (BFBFs). They enhance beneficial functions more than when they are in isolation. Thus, BFBFs can reduce chemical fertilizer (CF) inputs which cause to collapse soil microorganisms in agricultural ecosystems. A field experiment was conducted in a maize growing area in Sri Lanka (Anuradhapura), in order to evaluate the effects of BFBFs on plant growth and yield under application of different rates of CF (NPK) to maize crop. Reduced doses of CF (i.e. 75% and 50% of the recommended rate) with or without BFBFs application were compared with full dose of recommended CF (100%). Plant chlorophyll content, dry weight, seed weight and number of seeds per cob were measured as growth and yield parameters. Root associated nitrogenase activity was evaluated at flowering. Results showed that maize growth and yield with BFBFs + 50% CF were not significantly different from that of 100% CF, although 50% CF alone showed significantly lower performance. This suggests the potential of BFBFs to overcome nutrient deficiencies without affecting the maize yield. In fact, these results point towards a possible improvement of nutrient use efficiency in maize by BFBFs. This could also have been supported by the enhanced plant chlorophyll production in the presence of the BFBFs, even with the reduced doses of CF. Further, root associated nitrogenase activity was significantly higher with BFBFs + 50% CF than the other treatments. This helps to an improved BNF and hence microbial action in the rhizosphere. Thus, BFBFs application could lead to sustainable maize cultivation with low levels of CF and a better soil microbial community.
    16 th Australian Nitrogen fixation Conference, Q Station, Manly,Australia; 06/2012
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    U.V.A Buddhika
    World Congress on Biotechnology; 05/2012
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    ABSTRACT: Depleted fertility of maize grown soils is reflected by very low yields in absence of chemical fertilizers (CF). This has been attributed to collapse of microbial communities in soil/plant system with conventional cultural practices. To revive this, beneficial microbes are applied as biofertilizers. Recently, rhizospheric nitrogen fixers and fungi in the form of biofilmed biofertilizers (BFBFs) have been used in agriculture with promising results. Therefore, current study was conducted to evaluate the effect of developed BFBFs on restoring deteriorated soil/plant system in conventional maize. A greenhouse soil pot experiment was conducted to evaluate species richness of fungi, bacteria, cyanobacteria and microbial biomass carbon (MBC). Treatments were 100% recommended CF for maize, 50% CF and BFBF + 50% CF. Fungi and bacteria were isolated from plant rhizosphere, rhizoplane and histosphere whereas cyanobacteria from rhizosphere only. Colony forming units (CFU) of bacteria were counted. They were identified using morphological and biochemical characteristics whereas cyanobacteria by direct microscopic observations. The MBC of soil was estimated by using Chloroform fumigationextraction technique. Results showed that species richness of bacteria, fungi and cyanobacteria were higher in BFBF + 50% CF in all the locations tested. Further, the fertilizer reduction by 50% increased CFU significantly in rhizoplane, compared to that of 100% CF, whereas 50% CF + BFBF showed significantly highest counts of CFU in all the locations. Results confirmed the negative impacts of CF application on microbial biomass and diversity, thus inhibiting emergence of new species. The reduced dose of CF with BFBF can rehabilitate the deteriorated microbial community by enhancing biomass and species richness. Thus, microbial community development in this manner would benefit on plant productivity, environmental remediation and hence sustainability in conventional agroecosystems with cereals like maize. Further experiments under field conditions are needed to evaluate the effects and potentials of the BFBF on maize crop.
    Sri Lank-India conference on Agrobiotechnology for sustainable development , 12-13 March,, B.M.I.C.H., Colombo, Sri Lanka; 03/2012
  • U.V.A Buddhika
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    ABSTRACT: Maize is one of the most important cereals generally cultivated under rain fed smallholder conditions in Asia. There is an increasing trend in the application of high levels of nitrogen fertilizers to maize as it is a high nitrogen demanding crop. That suppresses nitrogen fixing microorganisms, which play a major role in plant growth and sustaining ecosystems. In agroecosystems, combining nitrogen fixers and fungal species in the form of fungal-bacterial biofilms (FBBs) has been shown to enhance beneficial effects. The current study focused on the effect of developed FBBs on maize seed germination and plant growth. Bacteria and fungi were first isolated from different sources, followed by screening for biological nitrogen fixation (BNF) prior to biofilm formation. Two FBBs (BF1 and BF2) were formed, which had two and seven bacterial species, respectively. Performance of the FBBs was compared with the seven bacterial species in monocultures for nitrogenase activity, seed germination and seedling vigor of maize. The FBBs showed significantly high nitrogenase activity, seed germination and seedling vigor. Further, biofertilizing potential of FBBs was investigated by conducting a greenhouse soil pot experiment under a reduced level of recommended chemical fertilizers (i.e. 50%). The FBBs showed a positive response in terms of total plant dry weight and photosynthetic efficiency. Thus, it seems that the FBBs exert beneficial effects through rhizosphere colonization, which leads to improved plant growth via increased seed germination and photosynthesis. Nitrogen fixation of the FBBs may have contributed to reduce chemical fertilizer requirement, thus sustaining maize plant growth. Further studies under field conditions are required to evaluate the efficacy of the FBBs in maize cultivation.
    Sri Lank-India conference on Agrobiotechnology for sustainable development 12-13 March,; 03/2012

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