Abstract
Abstract A description is provided for Alternaria porri . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Allium spp. including chive, garlic, leek, onion and shallot. DISEASE: Purple blotch of onion. The first symptoms are small, white lesions on the leaves; these, under wet conditions, develop into elliptical purplish areas, spreading to several centimetres long and with a yellowish border. Sporulation on these results in the formation of dark and light concentric zones. If conditions, after the initial appearance of symptoms, become dry (RH < 70%) then the white fleck lesions do not develop into the typical purple blotch. After 3 - 4 weeks the leaves collapse and infection can spread to the bulb, causing a deep yellow to reddish watery rot. The scales become desiccated and dark. Bulbs may be small or fail to develop. GEOGRAPHICAL DISTRIBUTION: Widespread, CMI Map 350, ed. 3; two new records not mapped are Nepal and S. Africa (47, 964). TRANSMISSION: The air-borne conidia increase with rain and wind and have a diurnal periodicity with a max. concentration between 0800 and 1400 hr, few being released between 2000 and 0600 hr (45, 1596). The pathogen is carried over from season to season in crop debris (40: 717).
Published Version
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