First Report of Aspergillus Vine Canker on Table Grapes Caused by Aspergillus niger in Europe

Abstract

In March of 2003, vine cankers and lesions were first observed on vigorous 1-year-old cv. Black Rose vines (Vitis vinifera) in a vineyard in southeastern Sicily, Italy. Since then, the same symptoms have been observed every year up to 2007 throughout the most important table grape production areas of Italy on cvs. Black Rose, Redglobe, and Italia. The disease epidemic has increased during the last 2 years, with incidence of cankered vines as much as 12.5%, and with two to three canker lesions per infected vine. On affected vines, most cankers were found at branch points and on the stems of young shoots grafted in the field. The infections seem to start from growth cracks on rapidly growing 1-year-old shoots or through wounds caused by the removal of lateral shoots. First symptoms usually appeared in late July or August as reddish pinhead-size drops of sap exuded from the infection site on the surface. By October to November, trunks of affected vines were girdled by the canker and prematurely displayed bright fall colors. The trunk appeared slightly larger and spongy where the canker occurred. Internally, cankered tissues were discolored and dead, and black powdery spores were abundant and sometimes visible on the surface. Callous tissue was often associated with the canker. Canker length was variable (average of approximately 8 cm) and either affected a small portion of the shoot's cross section or girdled it completely. Cultures of the fungus isolated from canker lesions or from the black spores within the lesions consistently yielded colonies typical of Aspergillus niger van Tiegh (3) when cultured on potato dextrose agar (PDA) supplemented with 100 μg/ml of chloramphenicol. Pathogenicity tests were carried out on potted plants of cvs. Black Rose, Redglobe, and Italia grown in a greenhouse by inoculating six vigorous, young grapevines of each cultivar. Inoculations were made by placing 8-mm-diameter mycelial plugs taken from actively growing cultures of A. niger on a cut made by removal of a lateral shoot with a sterile razor. Inoculated sites were sealed with Parafilm to prevent dehydration of the inoculum. For a control treatment, an equal number of grapevines was inoculated with only a PDA plug. Three months later, all inoculated grapevines exhibited symptoms similar to those observed in the commercial vineyards while control vines remained symptomless. A. niger was always reisolated on PDA media from all infected vines. A. niger is reported to cause bunch rot complex of grape (1,2) and was previously reported in California causing Aspergillus vine canker (4). Since disease incidence and severity can increase year after year on vines grafted in the field, it is recommended that all cankers be removed by cutting back the vines in the fall. In the following March to April, growers could revisit the affected vines, evaluate shoot growth, and vines with weak shoot growth should be cut back below the canker. Subsequently, the vine can be retrained using a shoot originating from below the canker. To our knowledge, this is the first record of Aspergillus vine canker caused by A. niger on table grapes in Europe.