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LEAF SPOTS at first greenish yellow, later yellow to brown, finally cracked, rugged, with crumbled away leaf fragments, developing along veins.
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ACERVULI (a) buff tofuscous black, up to 150 µm diam, composed of a stromatic layer, from which conidiophores arise, formed on the under leaf surface, mainly on vains. When young, the acervuli are covered with epidermis. Later, the epidermis cracks and exposes the conidioma of the fungus.
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CONIDIOPHORES (cp) erect, hyaline, 15-20 µm long, arranged in a palisade.
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CONIDIA (c) ellipsoidal, obpyriform, ovate to oblong, hyaline, aseptate, 9-14 x 4-6 µm, held in a creamy white gelatinous matrix.
PLANT HOST AND DISTRIBUTION. Discula platani affects different plant species of the genus Platanus (Agrios 1988).
Discula platani occurs in the whole world (Agrios 1988; Brooks 1953).
NOTES. The teleomorph of D. platani is Apiognomonia errabunda (Rob.) Hohn. (Smith et al. 1988).
Discula platani causes the most important disease of sycamore (Agrios 1988; Brooks 1953; Madej 1993; Smith et al. 1988).
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Apart from leaves, D. platani also affects twigs, causing twig blight before leaf emergence, and buds, killing them before they open. Leaves originating from infected buds are small, yellow to yellowish white, and short-lived. From the infected buds or leaves, the fungus spreads into the twigs on which it produces cankers.
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Strongly affected plane-trees early drop leaves, even in early summer. In trees severely affected for several successive years, many branches may die.
Discula platani overwinters as mycelium and immature perithecia in twig cankers and fallen leaves. In spring, the fungus forms perithecia with ascospores. The ascospores are liberated at the time when foliage is appearing. The fungus is favoured by rainy weather and rather cool temperatures.
REFERENCES
Agrios 1988. Plant pathology, 3rd edition, Academic Press, INC. San Diego, New York, Berkeley, Boston, London, Sydney, Tokyo, Toronto.
Brooks F. T. 1953. Plant diseases. Geoffrey Cumberlege. Oxford University Press. London, New York, Toronto.
Madej T. 1993. Badania do patologii Platanus x acerifolia. In: Madej T. Materialy do patologii i ochrony roslin oraz srodowiska, 72-100.
Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.
