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ISHS Acta Horticulturae 1149: II International Workshop on Bacterial Diseases of Stone Fruits and Nuts

Outbreak and etiology of brown apical necrosis on walnut in Balıkesir province of Turkey

Authors:   N. Ustun, D. Poyraz, N. Arslan
Keywords:   walnut, brown apical necrosis, etiology, identification
DOI:   10.17660/ActaHortic.2016.1149.11
Abstract:
In 2013 and 2014, severe brown apical necrosis (BAN) symptoms on walnut cultivar 'Pedro' fruits were observed in Balıkesir (Sındırgı), province of Turkey. The diseased fruits dropped prematurely. As a result, yield losses were estimated to reach nearly 50%. On some trees in the surrounding orchards leaf and shoot blight resembling walnut blight caused by Xanthomonas arboricola pv. juglandis (Xaj) or anthracnose by Gnomonia leptostyla were observed together with BAN symptoms. Samples from different diseased plant parts were subjected to isolation in order to determine the causal agent of the disease. Isolations performed from stigmatic end and inner wet rotting tissues of fruits as well as wet rotting on leaf petioles yielded yellow, mucoid colonies on YDC and several fungi on PDA. Yellow mucoid colonies were consistently isolated from blackish greasy leaf spots with angular appearance. Isolated bacteria were identified as Xaj on the basis of morphological, biochemical and pathogenicity tests on immature 'Pedro' fruits. Fungi isolated from internal fruit rotting tissues as well as wet rot on petiole were identified as Fusarium spp. or Alternaria spp. based on morphological characters. Only Fusarium spp. isolates were pathogenic on immature 'Pedro' walnut fruits. The results of the study demonstrated that BAN was primarily associated to Xaj and fungi like Fusarium spp. and Alternaria spp. co-existing on plant parts could be involved in the disease development under certain environmental conditions.

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