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Apical Necrosis and Premature Drop of Persian (English) Walnut Fruit Caused by Xanthomonas arboricola pv. juglandis

December 2011 , Volume 95 , Number  12
Pages  1,565 - 1,570

Concepció Moragrega, Institute of Food and Agricultural Technology-CIDSAV-XaRTA, University of Girona, Campus Montilivi s/n 17071 Girona (Spain); Josep Matias and Neus Aletà, Unitat de Producció Agroforestal, IRTA-Torre Marimon 08140 Caldes de Montbui (Spain); Emilio Montesinos, Institute of Food and Agricultural Technology-CIDSAV-XaRTA, University of Girona, Campus Montilivi s/n 17071 Girona (Spain); and Mercé Rovira, Unitat de Producció Agroforestal, IRTA-Torre Marimon 08140 Caldes de Montbui (Spain)



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Accepted for publication 11 July 2011.
Abstract

Etiological and epidemiological aspects of apical necrosis of walnut fruit were studied on cultivars Chandler, Franquette, and Hartley in a Spanish walnut orchard during 2007 and 2008. Affected fruit showed brown necrosis beginning at the blossom end of nuts; these symptoms differed from lesions of common blight of walnut (Xanthomonas arboricola pv. juglandis). X. arboricola pv. juglandis was consistently isolated from apical lesions throughout the growing season. Field isolates reproduced symptoms observed in the orchard when inoculated on immature detached walnut fruit in the laboratory. Sporadic occurrence of Fusarium spp. and Alternaria spp., mainly in dropped fruit, was attributed to secondary colonization of apical lesions that were originally caused by X. arboricola pv. juglandis. Apical necrosis and common blight were similar in disease epidemiology and cultivar susceptibility; a major increase in epidemics occurred at initial fruit development, and cvs. Chandler and Hartley were more affected than cv. Franquette. Our results suggest that apical necrosis is a new manifestation of walnut blight characterized by distinct symptoms and severe premature fruit drop.



© 2011 The American Phytopathological Society