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Disease Note. First Report of Stemphylium vesicarium on Garlic in South Africa. T. A. S. Aveling, Margaretha Mes Institute for Seed Research, University of Pretoria, Pretoria 0002. S. P. Naude, V.O.P.R.I., Private Bag X293, Pretoria 0001, South Africa. Plant Dis. 76:426. Accepted for publication 24 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0426E. During surveys for diseases of garlic (Allium sativum L.), a leaf
blight was repeatedly observed in the province of Transvaal.
Stemphylium vesicarium (Wallr.) E. Simmons was consistently isolated
from lesions varying from small and pale yellow to large, dark brown
to black, and ovate-elongate, often with a pinkish margin. Immersed
dark brown to black globose pseudothecia of the teleomorph,
Pleospora allii (Rabenh.) Ces. & De Not. (1), formed on potatodextrose
agar in 3-mo-old cultures. Pathogenicity of an isolate from
a garlic leaf (deposited with the National Collection of Fungi, South
Africa, designated PREM 50634) was shown by inoculating leaves
of 20 garlic plants (cv. Large Egyptian White) with conidia and
maintaining plants in a mist chamber for 48 hr. After 8 days, leaves
were severely diseased, with lesions similar to those seen in the field.
Cultures of S. vesicarium reisolated from these plants were identical
to the original. Our observations indicate that severe foliage damage
of garlic caused by this pathogen, with subsequent yield loss, occurs
only when leaf-wetness periods exceed 24 continuous hours and that
warm, humid summers are conducive to development of severe
epidemics. |