Nigrospora sphaerica Causing Leaf Spot and Twig and Shoot Blight on Blueberry: A New Host of the Pathogen

Abstract

Blueberries (Vaccinium corymbosum) have recently become an important alternative crop in different ecological regions of Argentina. In surveys, a new disease characterized by leaf spots and twig and shoot blight has been observed on plants cultivated in Arrecifes, Mercedes, and San Pedro (provinces of Buenos Aires) and Concordia (province of Entre Ríos) since July 2004. Spots initially appear brown, circular, 1 to 2 mm in diameter, and irregularly distributed on the leaves and they eventually coalesce. Fruiting twig and shoot blight developed from the tips toward the base. Affected plants of cvs. O'Neal and Reveille were distributed randomly in the field and with a low incidence (average of 2%). The objective of this work was to identify the causal agent of this disease. Symptomatic plant material was surface disinfested with 0.2% NaOCl for 1 min and 70% ethanol for 1 min, washed once with sterile distilled water, blotted dry with paper towels, and plated on potato dextrose agar. Colonies were initially white, becoming light to dark gray with the onset of sporulation with black, sphaerical to subsphaerical conidia that measured 14 to 19 × 12 to 16 μm. These characteristics agree with published descriptions of Nigrospora sphaerica (Sacc.) Mason (1,4). To evaluate pathogenicity, all leaves, petioles, and stems of seven healthy potted plants of cv. O'Neal were punctured with flamed needles and sprayed with a suspension of 1 × 108 spores of the fungus per milliliter of sterile distilled water. Another seven nonwounded plants were sprayed with the spore suspension. Seven plants similarly injured and seven nonwounded plants were sprayed with sterile distilled water and served as controls. Each plant was covered with a water-sprayed polyethylene bag and maintained in a controlled environment chamber at 20°C with a 12-h photoperiod. The bags were removed after 3 days. All wounded inoculated plants began to show disease symptoms similar to those observed in the field 20 days after inoculation. Controls and nonwounded inoculated plants remained symptomless. The pathogen was reisolated from diseased tissues fulfilling Koch's postulates. N. sphaerica is a well-known saprophyte on many plant species but has been mentioned as pathogen on many hosts (2,3). To our knowledge, this is the first reference of N. sphaerica as a wound pathogen of blueberry. In the field, the fungus would have gained access to the plant through wounds caused by insects or frost after a long-term wetness duration. References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CMI, Kew, Surrey, UK, 1971. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN, 1989. (3) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. ARS, USDA. 2007. (4) E. W. Mason. Trans. Brit. Mycol. Soc. 12:152, 1927.

Mycotoxigenic potential of fungi isolated from freshly harvested Argentinean blueberries

“…In Argentina, additional fungal diseases have been reported in blueberries, produced by Rhizoctonia solani, Fusarium solani, Pestalotiopsis guepini, Pucciniastrum vaccinii, Dothichiza caroliniana, Nigrospora sacchari, Nigrospora sphaerica, Rhizopus stolonifer, Botryosphaeria spp., Fusicoccum spp., Dothiorella spp., Phomopsis spp., Cylindrocladium spp., Curvularia spp., Phoma spp., Phytophthora spp., Aspergillus spp., and Penicillium spp. , Rivera et al 2009, Wright et al 1998, 2008b. Nevertheless, there are few reports on postharvest diseases of blueberries in our country (Munitz et al 2013, Rivera et al 2009, Wright et al 2008c.…”

Mercury affects the phylloplane fungal community of blueberry leaves to a lesser extent than plant age

“…Nigrospora spp. has been identified as pathogenic cause of leaf spot in Vaccinium corymbosum (blueberry plants) (Wright et al 2008). The increase of pathogenic species over time since Hg addition is likely associated with changes of an ageing leaf.…”

Disease Prevalence and Symptoms Caused by <i>Alternaria tenuissima</i> and <i>Pestalotiopsis guepinii</i> on Blueberry in Entre Ríos and Buenos Aires, Argentina

“…The other fungal species isolated from symptomatic blueberry organs have been identified as pathogens on V. corymbosum already. Blueberry was confirmed as a new host of N. sphaerica, on which it causes leaf spot and shoot blight [19]. B. cinerea was also reported on blueberry, as causative of flower and branch blights [34] and shoot blight caused by S. sclerotiorum was diagnosed [35].…”

“…tenuissima was by far the most frequent species isolated from leaves, and it was highly present on fruits as well; and P. guepinii was comparatively less important on both organs. A. tenuissima has been identified causing leaf spots on blueberry in Argentina [19], China, the United States and New Zealand [17]. Pestalotiopsis sp.…”

“…The isolates had been obtained from diseased organs, and had been already confirmed as pathogenic on blueberry [19] [20]. Healthy blueberry plants were inoculated with A. tenuissima, P. guepinii or A. tenuissima + P. guepinii.…”