First report of Alternaria alternata causing leaf blight of potatoes in South Africa.

摘要

During recent growing seasons, a new leaf blight was observed on potatoes in various production regions in South Africa. Symptoms were observed before early blight, from 50 to 60 days after emergence of the potato plants. Typical leaf symptoms were small, circular, brown lesions, first visible on the abaxial sides of leaves. During favourable environmental conditions, severe infections were seen as coalesced lesions and blighted leaves and stems. Isolations from leaf lesions were made. Alternaria alternata was consistently isolated and preliminarily identified based on the morphological characteristics. Morphological identification was confirmed by amplification of the ITS region. PCR products were sequenced and the identity of isolates confirmed by a BLAST search on the GenBank database. Koch's postulates were confirmed by inoculation of healthy potato cv. BP1 leaves. Leaf blight symptoms similar to those observed on diseased potatoes in the field began to develop at 3 weeks after inoculation. Isolations made from these lesions consistently yielded A. alternata.This is thought to be the first report of A. alternata causing leaf blight on potatoes in South Africa.Digital Object Identifier http://dx.doi.org/10.1094/PDIS-11-10-0820