Botany

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    Effects of Fusarium moniliforme culture extracts and fumonisin B1 on DNA, RNA and protein synthesis by baby hamster kidney cells
    (Springer Netherlands., 1998) Abeywickrama, K.; Bean, G.A.; Kennedy, K..A.
    Baby hamster kidney cells (BHK-21) were exposed to culture filtrates of 4 Fusarium moniliforme isolates containing varying levels of fumonisin B1 (FMB1) and the effects upon RNA, DNA and protein synthesis were monitored. Cells were also grown on medium amended with FMB1 only for comparison. After 24 h incubation FMB1 (100 μg/100 ml medium) reduced protein synthesis by 4% and by 18% after 48 h. Culture filtrates containing the highest levels of FMB1 also caused the greatest inhibition in protein synthesis after 24 h but after 48 h protein synthesis levels were the same as controls even though the FMB1 level was 360 μg/100 ml. Only FMB1 reduced DNA synthesis, by 8% after 24 h but after 48 h DNA levels had increased by 40 % over controls. The culture filtrates containing the highest levels of FMB1 (360 μg/100 ml) reduced DNA synthesis more than 50% after 24 h and 48 h. Culture filtrates containing lesser amounts of FMB1 in some instances stimulated DNA synthesis and inhibited it in others. There was also no correlation in the level of FMB1 with the inhibition of RNA synthesis by BHK cells. It appears that metabolites other than fumonisin produced by F. moniliforme in culture can affect and both stimulate and inhibit RNA, DNA and protein synthesis by BHK cells.
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    Inhibition of aspergillus flavus link and aflatoxin formation hy essential oils of cinnamomum xeylanicum (L) and cymbopogon nardus rendle
    (Postgraduate Institute of Agriculture, University of Peradeniya: Peradeniya, 2002) Jayaratna, K.H.T.; Pranagama, P.A.; Abeywickrama, K.P.; Nugaliyadde, L.
    The essential oils of Cinnamomum zeylanicum (L.) leaf and Cvmbopoeon nardus Rendle were tested for their fungistatic, fungicidal and qflatoxin suppressing efficacy against an isolate of Aspergillus flavus Link, isolated from rice. The mycelial growth and the aflatoxin formation in SMKY semi synthetic liquid medium in the presence of different concentrations of two test oils were monitored. At concentrations varying from 100 to 500 ppm of the essential oil of C. zeylanicum. the mycelial dry weight decreased from 0.49 to 0.01 g/50 ml. The percentage inhibition of the mycelial growth of A. flavus increased from 50 to 95 when treated with 1000 to 1800 ppm of C. nardus oil. The minimum lethal concentrations (MLCs) for the essential oils of C. zeylanicum leaf and C. nardus were 1000 and 4000 ppm, respectively. Aflutoxins were not present in the medium at or above the concentrations of400 and 600 ppm C zeylanicum leaf and C nardus oils, respectively
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    The effect of spraying essential oils of Cymbopogon nardus, Cymbopogon flexuosus and Ocimum basilicum on postharvest diseases and storage life of Embul banana
    (The Journal of Horticultural Science and Biotechnology, Taylor & Francis., 2003) Anthony, S.; Abeywickrama, K.; Wijeratnam, S.W.
    Embul banana hands were sprayed with emulsions of the essential oils of Ceylon citronella (Cymbopogon nardus) (0.4% v/v) lemon grass Cymbopogon flexuosus (0.16% v/v), or Indian sweet basil (Ocimum basilicum) (0.16% v/v) and stored cool (13.5 ± 1°C) or at ambient temperature (28 ± 1°C) at 94% relative humidity. A benomyl spray (0.1% w/v) was included as a standard fungicide control treatment. The effects of the essential oils on post-harvest diseases, and on organoleptic and cosmetic quality and various properties of the fruit (percentage weight loss, changes in fruit firmness, total soluble solids and titratable acidity) were determined. Treatment with Ocimum basilicum oil controlled crown rot and anthracnose, enabling bananas to be stored for up to 21 d at 13.5 ± 1°C without any detrimental effect on their organoleptic properties; results were comparable with treatment with benomyl. Rapid-ripening induced by ethral after cool storage resulted in better quality bananas. The oil of C. nardus affected the texture and flavour of the fruit and that of C. flexuosus did not give complete control of crown rot. Spraying Embul bananas with emulsions of the essential oil of Ocimum basilicum prior to cool storage can be recommended therefore as a safe, cost-effective method, with commercial potential, for controlling post-harvest diseases and extending storage life.
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    Deterrent effects of some Sri Lankan essential oils on oviposition and progeny production of the cowpea bruchid, Callosobruchus maculatus (F.)(Coleoptera; Bruchidae)
    (2003) Paranagama, P.; Adhikari, C.; Abeywickrama, K.P.; Bandara, P.
    Essential oils extracted from five plant materials were tested on oviposition and progeny production of F1 adult of cowpea bruchid, Callosobruchus maculatus on cowpea seeds. All oils tested showed a significant inhibition of oviposition and F1 adult emergence compared to the control during no-choice tests. Cymbopogon citratus and C. nardus showed higher effect on oviposition and F1 adult emergence than the essential oils of Alpinia calcarata, Cinnamomum zeylanicum and Murraya koinigii. In the choice test, the percentage ovipositions in all oils treated samples (except 10 mg of M. koinigii) were significantly lower than that of the control and ethanol treated samples. The percentage eggs deposited decreased with increasing doses of the oils ranging from 10 to 160 mg. The percentage of eggs laid was zero in samples treated with 40 mg of C. nardus or A. calcarata, 80 mg of C. citratus and 160 mg of C. zeylanicum. The essential oils of M. koinigii showed the lowest effect on oviposition when compared to other four essential oils.
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    Cymbopogon citratus (lemongrass) and citral a+ b spray treatments alone or in combination with sodium bicarbonate in controlling crown rot in Embul banana (Musa acuminata AAB)
    (2004) Abeywickrama, K.P.; Kularathna, L.; Sarananda, K.; Abeygunawardena, D.
    The mounting pressure against synthetic fungicidal dips and sprays, restrict their use in controlling crown rot, a major post-harvest disease in banana. Generally regarded as safe (GRAS) compounds have a great potential to be used as alternatives to fungicides. Identification of chemical constituents of Cymbopogon citratus oil revealed the presence of citral as the main component. Cymbopogon citratus and citral with sodium bicarbonate (SBC) was fungicidal against the 3 banana fungal pathogens at 0.10-0.20 % v/v and 0.07-0.08 % v/v respectively. Embul banana sprayed with C. citratus alone or in combination with SBC after induced ripening, indicated a crown rot severity of 25 - 5 0% whereas, citral treatment resulted in a slightly lower disease severity. The physico-chemical parameters tested were not affected by the treatments. Oil/citral, SBC treated bananas and control were ranked good to excellent with respect to odour, flavour, taste and overall acceptability. The low disease severity of crown rot due to spray treatment of citral and SBC highlights the importance in adapting this simple, alternate treatment strategy for quality maintenance.
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    Aflatoxigenic Aspergillus flavus and aflatoxin formation in selected spices during storage
    (2009) Rajasinghe, M.; Abeywickrama, K.P.; Jayasekera, R.
    Proliferation of aflatoxigenic fungi and accumulation of aflatoxins take place during storage of spices at various environmental conditions. The objective of this research was to identify the aflatoxigenic fungal species and their aflatoxin forming potential in selected spices during storage in the laboratory and refrigerator. Dilution series of spice samples namely chilli (Capsicum annum) powder, curry powder, turmeric (Curcurma longa) powder and pepper (Piper nigrum) powder (purchased from two producers) were prepared separately and the frequency of occurrence of aflatoxigenic and other fungi were assessed after plating each on Potato Dextrose Agar and incubating at ambient temperature. Aflatoxin formation of A. flavus was confirmed by growing a pure culture on a SMKY medium and identifying toxins on thin layer chromatographic plates. The presence of aflatoxins in spice samples stored at 30 ± 20C and 40C was also confirmed. Long storage of spices leads to aflatoxin production irrespective of storage temperature hence, it is advisable to consume spices such as chilli powerder, tumeric etc. within a relatively short period to avoid build up of aflatoxins.
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    Polyphenol oxidase inhibitory activity of essential oils of Cymbopogon nardus and Cymbopogon citratus
    (Journal of Tropical Medicinal plants, 2003) Ranasinghe, L.S.; Jayawardena, B.M.; Abeywickrama, K.P.
    Polyphenol oxidase (tyrosinase) (EC 1.14 18.1) is responsible for the hyperpigmentation in humans, insect molting process and browning reactions of plants. There is interest to develop methods to control polyphenol oxidase reaction. Essential oils of lemon grass, Cymbopogon citratus (D.C.) Stapf. and citronella, Cymbopogan nardus Rendle were found to inhibit the activity of polyphenol oxidase. Cinnamic acid inhibited the oxidation with an ID value of 0.351 (mg/ml). Citronella and lemongrass oils could be used as naturally occurring inhibitors for Polyphenol oxidase.
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    The efficacy of essential oil of Alpinia calcarata (Rosc.) and its major constituent, 1,8-cineole, as protectants of cowpea against Callosobruchusmanculatus(F.) (Coloeptera; Bruchidae)
    (Canadian Journal of Plant Science, 2006) Abeywickrama, K.P.; Adhikari, A.A.C.K.; Paranagama, P.A.; Gamage, C.S.P.
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    Taxonomic complexity of powdery mildew pathogens found on lentil and pea in the U.S. Pacific Northwest
    (Phytopathology, 2008) Attanayake, R.N.; Glawe, D.A.; McPhee, K.E.; Dugan, F.M.; Chen, W.
    and field production conditions in the U.S. Pacific Northwest was investigated using morphological and molecular characters. Isolates collected from lentil plants grown in the greenhouse or field displayed morphologies in substantial agreement with descriptions of Erysiphe trifolii, but sometimes with more extensively branched chasmothecial appendages resembling those of E. diffusa. ITS sequences of the lentil fungi were identical to each other, and more similar to GenBank accessions of E. trifolii (99.5%) than of E. diffusa (97%). The data suggest there may be more than one Erysiphe species causing lentil powdery mildew. The fungus on field-grown pea plants was determined to be E. pisi. However, powdery mildew samples obtained from greenhouse pea plants were either E. pisi or E. trofolii depending on the time of sampling and greenhouse location. Therefore, the powdery mildews infecting lentil and pea are more diverse than previously assumed. Powdery mildews from black medic (Medicago sp.) and sweet clover (Melilotus sp.) found near the greenhouses exhibited ITS sequences with 99.9 to 100% similarity to isolates from lentil and pea in the greenhouses, and to isolates from lentil from the field. These weedy legumes could be inoculum sources for powdery mildew of lentil and pea in the greenhouses, and serve as alternative hosts for cultivated legumes.
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    Potential alternative hosts for a powdery mildew on pea
    (Phytopathology, 2009) Attanayake, R.N.; Glawe, D.A.; Dugan, F.M.; Chen, W.
    Powdery mildew of pea (Pisum sativum) is an important disease in the field and in the greenhouse. The most widely documented powdery mildew on pea is Erysiphe pisi, but E. trifolii and E. baeumleri have also been reported. From greenhouse-grown peas, we obtained powdery mildew samples with rDNA ITS sequences nearly identical to previously deposited sequences of E. trifolii. Because detailed studies on host range of this pea powdery mildew in the US Pacific Northwest were lacking, we tested common legume plants from the region as potential alternative hosts. Eleven species were used in greenhouse cross inoculation studies: Lens culinaris, Glycine max, Melilotus albus, M. officinalis, Medicago polymorpha, M. lupulina, M. scutellata, Lathyrus latifolius, Trifolium pratense, Vicia cracca, and V. faba. Except for Glycine max, all the plant species tested developed powdery mildew lesions in 10?14 days after inoculation. Susceptibilities of two of these species (L. culinaris and M. albus) were also confirmed with detached leaf assays. Results showed that all the above legumes (except soybean) are potential alternative hosts for the E. trifolii found on pea. Powdery mildews found on wild legumes (Meliotus albus and Medicago lupulina) were also confirmed to be E. trifolii, suggesting that the wild legumes could be inoculum sources of powdery mildew on greenhouse pea plants during winter months. These findings have implications in managing powdery mildew of pea.