PURSE 2013
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Browsing PURSE 2013 by Subject "Agriculture"
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- ItemDoes oxidizing power of roots affect the iron toxicity tolerance of rice?(The University of Peradeniya, 2013-07-04) Wijerathna, Y. U. C.; Dandeniya, W. S.; Mithrasena, Y. J. P. K.Iron toxicity decreases the average rice yield in the low country wet zone of Sri Lanka from its potential of 10 t ha-1 to 2.5 t ha-1. Management of iron toxic soils will not be successful until a clear understanding of the mechanisms to tolerate iron toxicity is gained. A study was conducted with the aim of determining the effect of the oxidizing power of roots on iron toxicity tolerance by rice. Three varieties of rice with varying iron toxicity tolerance were used in an experiment conducted at the Regional Rice Research and Developing Centre, Bombuwela. The varieties were Bw 267-3 (tolerant), Bw 272-6b (susceptible) and Bw 363 (moderately tolerant). Rice seedlings were grown in a nursery maintaining aseptic conditions. To test the iron toxicity tolerance by rice varieties 21 day-old seedlings were transplanted in sand culture maintained at saturated condition and enriched with three iron treatments; 0, 75 and 300 ppm of Fe2+ supplied as in four replicates. Plants were irrigated with standard IRRI solution with the respective iron treatment twice a week until 40 days after germination (DAG). At 40 DAG plants were uprooted and oven dry weights, shoot Fe, P and K contents were measured. Potential rhizosphere oxidizing power of three rice varieties was assessed following the method suggested by Trolldenier (1987). Analysis of variance was done to determine the significance of treatment effects and LSD was used for mean separation. At 40 DAG, the biomass production decreased by nearly 50% with increasing iron levels from 0 to 300 ppm in all three varieties. Bw 272-6b showed iron toxicity symptoms and higher tissue Fe2+ contents than the tolerant varieties but Fe2+ levels were not significantly different (p<0.05). There was a significant interaction between variety and iron treatment on nutrient uptake by rice (p<0.05). Oxidizing power of roots as indicated by the width of the clearing zone was significantly different among varieties. Tolerant Bw 267-3, had the highest oxidation potential (5.3±0.9 cm) followed by moderately tolerant Bw 363 (3.7±0.9 cm) and susceptible Bw 272-6b (2.5±0.6 cm). Hence, there is a positive relationship between oxidizing power of roots and iron toxicity tolerance. Even though the results from the present work suggest the use of oxidizing power of roots as a potential parameter for in vitro screening of a large number of rice varieties for iron toxicity tolerance, further studies with a larger germplasm with varying iron toxicity tolerance is recommended.
- ItemInvestgations on the causes of discolouration of rice grain(The University of Peradeniya, 2013-07-04) Gunarathne, L. H. S. N.; De Costa, D. M.; Dissanayake, D. M. N.The grain quality of rice is severely reduced due to discoloration of grains, an emerging problem of many rice growing areas of Sri Lanka. The objectives of the present study were to identify microorganisms causing grain discoloration of rice grown in Sri Lanka and to identify effective control measures. Seeds of four varieties of rice (i.e. Bg 300, Bg 352, Bg 357 and Bg 358) were collected from rice fields of RRDI, Batalagoda. Fungi and bacteria associated with discoloured grains were isolated by the standard blotter method and the PDA plate method. Efficiency of the commercially available fungicide (i.e. 50% CarbendazimWP) and a biological control agent (i.e. Bacillus subtilis) was determined using a pot experiment to control grain discolouration. The efficiency of the commercially available fungicide (i.e. 50% CarbendazimWP) and a biological control agent (i.e. Bacillus subtilis) was determined using a pot experiment to control grain discolouration. Fusarium moniliforme, Penicillium spp., Helminthesporium oryzae, Aspergillus flavus and Aspergillus niger were isolated as commonly-occurring fungal species and Burkholderia cepacia was isolated as a bacterial species from discoloured rice seeds. Fusarium moniliforme was recorded as the fungus present at the highest frequency in all rice varieties tested. Efficiency of the commercially available fungicide (i.e. 50% CarbendazimWP) and a biological control agent (i.e. Bacillus subtilis) was determined using a pot experiment to control grain discolouration. Carbendazim was found to be more effective than the bacterial antagonist in reducing rice grain discolouration. Treating the four rice varieties with 50% Carbendazim (1mg in 300 ml of water) resulted in a 64-96 % reduction of grain discolouration in comparison to the reduction given by the bacterial antagonist (i.e. 57-94%).
- ItemMetabolomics of Sri Lanka tea germplasm : a quantitative analysis of catechins, gallic acid and caffenine(The University of Peradeniya, 2013-07-13) Jeganathan, B.; Punyasiri, P. A. N.; Kottawa-Arachchi, J. D.; Ranatunga, M. A. B.; Abeysinghe, I. S. B.; Gunasekare, M. T. K.; Bandara, B. M. R.Tea (Camellia sinensis L.) contains a myriad of metabolites of varying chemical structures. Early efforts to correlate metabolites with the quality of tea have been focused on single metabolite variation in tea cultivars. The literature available on the analysis of a broad range of metabolites in tea accessions is minimal. We have begun a systematic study on metabolic profiling of the Sri Lankan tea germplasm through the analysis of principal metabolites of tea leaves. The results of this study will enable, the commercial exploitation of germplasm accessions for making diverse products of tea of desired quality, the definition of biochemical diversity of the Sri Lankan tea germplasm, the stratification of germplasm accessions into diverse clusters, and the identification of parent candidates for breeding programmes. We report our preliminary results on the quantitative analysis of tea flush from 40 germplasm accessions for total polyphenol content (TPP) and six metabolites. Green leaf samples of 40 germplasm accessions collected from the ex situ field genebank of the Tea Research Institute of Sri Lanka were analysed for total polyphenols using the Folin Ciocalteu’s colorimetric method (ISO 14502-1), and for six metabolites to include 4 catechins, caffeine and gallic acid, using high performance liquid chromatography (ISO/CD 14502-2). The measurements were made for two extracts prepared from each accession. The TPP was found to be 165.16 - 275.78 mg/g (w/w, dry weight). The contents of the six metabolites varied in the following ranges: epigallocatechin gallate (EGCg, 37.18±2.70 - 109.44±8.35 mg/g), epigallocatechin (EGC, 6.11±0.43 - 47.60±0.20 mg/g), epicatechin gallate (ECg, 13.73±3.66 - 43.52±4.00 mg/g), epicatechin (EC, 4.44±0.42 – 21.88±1.27 mg/g), caffeine (13.72±0.53 – 43.48±1.48 mg/g) and gallic acid (0.10±0.03 - 1.56±0.12 mg/g). The highest contents of EGCg, ECg, EGC and EC were observed for the accessions TRI62/9, TRI62/9, TRI4076 and TRI777 while the lowest amounts were shown by the accessions KEN16/3, PBGT41, PLLG2 and PLLG2, respectively. High levels of EC and ECg were observed in high-quality black tea producing cultivars whereas low-quality tea producing cultivars had low levels of EC and ECg.
- ItemNutrient release from soil as affected by the composition of organic amendment(The University of Peradeniya, 2013-07-04) Mariaselvam, A. A.; Dandeniya, W. S.; Indrarathne, S. P.Organic materials contribute to soil fertility by influencing nutrient availability. Composition of the organic amendments affects soil microbial activity and nutrient dynamics. Therefore, nutrient release from soil may differ with different organic amendments. The objective of this study was to determine the effect of different types of organic materials on soil nutrient release. Soil was collected from an Ultisol in an agricultural field in Wagolla (Low Country Wet Zone of Sri Lanka). Organic amendments used were cattle manure (C), cattle manure-rice straw (CR) (2:1) cattle manure-wood shaving (CW) (2:1) cattle manure–rice straw-wood shaving (CRW) (4:1:1) as fresh material or material incubated for two months. 50 g soil was mixed with organic amendment (1% w/w) in triplicate and was used to set up leaching columns arranged in a complete randomized design. At the 1st, 2nd, and 8th week of incubation soil was leached with 150 ml distilled water. Leachates were analyzed for available NO3--N, P and K. Soil microbial respiration was measured in an incubation experiment using the same treatments up to 8 weeks. Nutrient release declined over time and the trends were significantly affected by the treatment. Release of K during the first two weeks was higher in soils amended with fresh C followed by incubated CR, C and CRW treatments. Incubated C and CRW supplied more P than other treatments. N release in the first week was highest in soil only treatment as compared to soils incubated with organic amendments indicating immobilisation. Except for CW, N immobilisation was less when using incubated material. Soil microbial activity as reflected by the respiration rate was enhanced by organic amendments. Higher respiration rates in first and second week of incubation were noticed when soil was amended with an organic material (175-370 μg/g/day and 273-448μg/g/day respectively) compared to soil only treatment (117 and 136 μg/g/day respectively). The complexity of the organic amendment differently affects the release of different nutrients. This is partly due to the nutrient content of the amendment and partly due to microbiologically mediated processes like mineralization-immobilisation. In general, incubation of organic amendments prior to application resulted in high P and K release in soil.
- ItemSoil fertility constraints identified for a low productive alfisol at Mahailluppallama(The University of Peradeniya, 2013-07-04) Chathurika, J. A. S.; Indraratne, S. P.; Dandeniya, W. S.Low productive soils exist throughout the world and many of these soils are low in organic matter and nutrients. These fertility constraints can be resolved using an appropriate supply of nutrients. This study was conducted to identify soil fertility constraints of a low productive field from the low country dry zone of Sri Lanka. Soil samples were collected from the Field Crops Research and Development Institute at Mahailluppallama. Two sites were selected representing a low productive field (LPF) and a comparatively high productive field (HPF), based on farm records. From each field 16 soil samples were collected at 0-20cm depth using a grid method to prepare a representative composite sample. Six sub-samples from the composite sample were analyzed for pH, organic-matter (OM), cation exchange capacity (CEC) electrical conductivity (EC) and texture. Available nutrients were determined using three extractions; P, K, Cu, Fe, Mn and Zn were extracted with 0.25 M + 0.01M EDTA + 0.01M , 0.1M KCl extraction used for , Ca and Mg and 0.08 M extraction for S. Critical values considered for N, P, K, Ca, Mg, S, Fe, Mn, Cu and Zn were 100, 48, 156, 701, 182, 40, 30, 12, 3 and , accordingly. There was no significant difference between the two fields for OM%, sand % and EC. The pH, CEC, clay % and silt % were significantly different (p<0.p5) between the two fields but pH and CEC were within the favourable range for cropping in both fields. Soil in LPF is sandy clay loam in texture while that of HPF is sandy loam. The higher clay content in LPF (27%) as compared to the HPF (20%) may be linked to poor infiltration rates reported for LPF and may have caused its low productivity. Concentrations of S, K, Mg, Ca, Zn and Mn were significantly different (p<0.05) between the two fields. Further both fields were deficient in N, P, S, Ca and Zn in comparison to the critical values. Hence, nutrient deficiencies could be limiting the productivity of both fields. Implementing site-specific fertilizer recommendations, addition of silt-sized organic matter pellets or rock powder, and planting in raised beds could be adopted to increase the productivity of LPF.