Occurrence and Etiology of Brown Apical Necrosis on Persian (English) Walnut Fruit

Abstract

In 1998, a severe fruit drop was observed in Italy, principally on cv. Lara Persian (English) walnut (Juglans regia). Dropped fruit showed a brown patch at the blossom end and blackening and rot of inner tissues. The disease, called brown apical necrosis (BAN), was investigated on fruit collected in Italy and France in 1999. In 2000, studies were carried out in three walnut orchards located in Italy and in France to substantiate the etiology of BAN. Isolations performed from inner diseased fruit tissues yielded several fungi, in decreasing frequency of isolation: species of Fusarium and Alternaria, and one species each of Cladosporium, Colletotrichum, and Phomopsis. However, only Fusarium spp. were recovered from stigmas of BAN-affected fruit. The fungi associated with BAN-diseased fruit and species composition differed among locations and over time, confirming results obtained in previous investigations. The species of Fusarium used in pathogenicity tests reproduced BAN-disease symptoms when inoculated on fruit, whereas an Alternaria alternata isolate caused only limited necrosis of the style. However, the role of the other fungi commonly isolated from BAN-diseased fruit remains to be defined. The walnut blight pathogen, Xanthomonas arboricola pv. juglandis, occasionally was isolated from BAN-diseased fruit. No correlation was found between the extent of external brown patches and the size of inner lesions. Repeated isolations from and inoculations of fruit demonstrated that BAN can be considered a complex disease, and the inner infections originate from the style of the fruit.

First Report of Apical Necrosis in Walnut Cultivars from Northern Argentinean Patagonia

“…This description matches with the symptoms found in fruits with brown apical necrosis from cultivars of Italy, described by Belisario et al [7]. Although necrosis at the apical end is always present, there is no definite correlation between the extent of external and internal lesions [7].…”

“…With respect to internal symptoms, the infection progresses through the tissues and can reach the seed, causing a brown or black rot of the seeds [6,8]. This description matches with the symptoms found in fruits with brown apical necrosis from cultivars of Italy, described by Belisario et al [7]. Although necrosis at the apical end is always present, there is no definite correlation between the extent of external and internal lesions [7].…”

“…During the last years, it has been reported a new disease that affects walnut trees causing premature fruit to drop and significant yield losses in Mediterranean regions such as Spain, France, Turkey [5,6] and Italy [7]. The typical symptoms of this pathology consist of an apical necrosis that originates at the stigmatic end of the fruits.…”

“…The typical symptoms of this pathology consist of an apical necrosis that originates at the stigmatic end of the fruits. A characteristic apical necrosis that causes severe fruit fall was defined by Belisario et al [7] as Brown Apical Necrosis (BAN) and was recently described in some walnut producing regions of Spain and Italy. Brown apical necrosis was first reported and observed in Italy in 1998 [7].…”

Phylogenetic and Variable-Number Tandem-Repeat Analyses Identify Nonpathogenic Xanthomonas arboricola Lineages Lacking the Canonical Type III Secretion System

“…Previous studies showed that X. arboricola pv. juglandis has been also isolated from tissues affected by brown apical necrosis (29)(30)(31). Hajri et al (10) reported the association of X. arboricola pv.…”