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Purple blotch ( Alternaria porri ) of onion in Kenya
Author(s) -
BOCK K. R.
Publication year - 1964
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1964.tb01195.x
Subject(s) - biology , mancozeb , horticulture , fungicide , alternaria , lesion , spots , conidium , incubation period , incubation , germination , botany , veterinary medicine , psychology , biochemistry , psychiatry , medicine
SUMMARY In 1961 an epidemic attack by Alternaria porri occurred on irrigated onions at Baringo in the Rift Valley, Kenya. Two distinct lesion types appeared: (1) typical purple or brown blotches; (2) white, irregular spots or flecks. These were present in varying proportion, depending on the duration of conditions favourable to infection, and subsequent relative humidity. High R.H. favoured the development of purple blotches; low R.H. for prolonged periods after infection usually resulted in white flecking only. These flecks were often sterile, making diagnosis difficult. Germination, appressorial and lesion formation displayed a broad optimum temperature (21–30° C). Resistance to the disease shown by a number of American hybrid onions was governed by cuticle thickness; this resistance was reduced by wounding—such as is associated with sand‐storm blast—or by incubation after infection for prolonged periods at high R.H. Two fungicides, mancozeb and dicloran, effectively controlled the disease in the field.