Faculty of Science

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https://ir.lib.pdn.ac.lk/handle/20.500.14444/213

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Browsing Faculty of Science by Subject "Botany"

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    Biology of plumeria leaf rust disease caused by coleosporium plumeriae
    (University of Peradeniya, 2006) Weeraratne, T. P.; Adikaram, N. K. B.
    The leaf rust disease in Plumeria first appeared in Sri Lanka some time in the year 2002 and is now widespread. The disease is found in both Plumeria rubra and P. obtusa (Apocynaceae) and the infected leaves show numerous tiny, raised, orange, rusty pustules on the abaxial surface of the leaf. The adaxial surface opposite to infected sites is chlorotic reducing the available photosynthetic area of the leaf. Symptoms were absent in the stem or flowers. The causal agent was identified as Coleosporium plumeriae. This is the first report of Plumeria leaf rust in Sri Lanka. Microscopic studies indicated the presence of uredia, formed from the transversing mycelium and emerged through ruptured lower epidermis. No other fruiting structures, telium, aecium or spermatium were encountered at any stage of the disease in Plumeria or in Pinus, which was previously reported as a secondary host of C. plumeriae. Two other fungi, Absidia sp. and Verticillium sp., were found to colonize the rust areas of more mature leaves in succession, Absidia sp. appearing first. These two fungi grew as mycoparasites on C. plumeriae and had no direct contact with the leaf tissue. However, colonization by these two fungi resulted in necrosis around the rust infections inflicting damage to leaves. Young leaves down to about the third from the apical bud are resistant to rust infection. Young leaves contain more latex compared to mature leaves and the latex shows inhibitory action against germination of uredospores. Latex was found to possess chitinase activity on a gel diffusion assay. Latex may therefore be playing a role in the resistance of young leaves against rust infection.
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    Occurrence of Leaf Blotch Disease (Botryosphaeria sp. ) in Ficus religiosa in Sri Lanka
    (University of Peradeniya, 2009) Maharachchikumbura, S. S. N.; Adikaram, N. K. B.
    This paper reports the occurrence of a leaf blotch disease in Ficus religiosa in Sri Lanka. The disease first appears as small, irregular, yellow specks in leaves at later stages of maturity and with time the infected areas become necrotic and gradually enlarge. At advanced stages the whole leaf turns yellow with brown blotches and is shed. The causal agent was identified as Botryosphaeria sp. The necrotic blotches are associated with erumpent fruiting bodies of the fungus, ascomata. Ascomata are solitary or botryose and are found on both sides of leaves. Asci are with numerous pseudoparaphyses and ascospores were observed. Colony developed on water agar medium showed hyaline, aseptate conidia and mature brown conidia. In the presence of leaf blight caused by Glomerella cingulata, the leaf blotch symptoms appeared much later, about 10-12 weeks after the new flush. The diseased leaves do not last long as F. religiosa, being a deciduous species, sheds leaves seasonally. However, the fallen leaves, unless eliminated, may provide a good source of inoculum for infection of the new flush. Commercial fungicide, BULLET 50, inhibited the in vitro growth of Botryosphaeria sp. This is the first report on a blotch disease attacking leaves of F. religiosa in Sri Lanka.