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Brown Apical Necrosis (BAN) a new problem in English walnut (Juglans regia L.) production in the Biobio Region of Chile

Ernesto Moya-Elizondo: Universidad de Concepción

<div>English (Persian) walnut plantations have had an explosive growth in the Biobío Region in Chile, going from 107 hectares to almost 2,000 in the last 10 years. Walnut blight, caused by <em>Xanthomonas arboricola</em> pv. <em>juglandis</em>, has been the main phytopathological problem affecting these nuts, but from 2013 to date premature fruit dropping during fruit growth in spring, associated with a brown to dark necrosis in the apical area of nuts has been consistently observed. Isolation of different <em>Fusarium</em> and <em>Alternaria</em> species in dropped fruit suggests the presence of the disease complex Brown Apical Necrosis (BAN) in this area. During the 2016/17 season, a follow-up of 16 English walnut trees cv. Chandler and three cv. Serr in a commercial orchard located in Negrete (Biobío Region), showed that between 60 and 100% of the fruits that fell to the ground between November 28 and January 2 were colonized by <em>Fusarium</em> and <em>Alternaria</em> species. Morphological and molecular analysis (ITS, NS, and β-tubulin genes) of fungal isolates obtained from walnut fruits indicate the presence of <em>F. oxysporum</em>, <em>F. culmorum</em>, and <em>A. alternata</em> as part of BAN disease complex in central-southern Chile. A study determined that inoculations with a field isolate of <em>F. oxysporum</em> and <em>A. alternata</em> during the flowering period, reproduced BAN symptoms in a 68.8% and 55.4%, respectively. Actually, we are working in epidemiological studies of BAN disease complex and developing control strategies for its proper management.</div>