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First Report of Coniella granati Fruit Rot and Dieback on Pomegranate in the Western Cape of South Africa

Author:
Lennox, C. L., Mostert, L., Venter, E., Laubscher, W., Meitz-Hopkins, J. C.
Source:
Plant disease 2018 v.102 no.4 pp. 821
ISSN:
0191-2917
Subject:
Coniella, Punica granatum, agar, bark, conidia, cultivars, dieback, ethanol, fruits, genes, greenhouses, humidity, hyphae, industry, internal transcribed spacers, mycelium, orchards, pathogenicity, peptide elongation factors, petrolatum, plant pathology, plant rots, pomegranates, postharvest diseases, pycnidia, sodium hypochlorite, translation (genetics), trees, Asia, Europe, South Africa, United States
Abstract:
Shoot dieback and necrotic black lesions were observed on pomegranate trees (Punica granatum Linn.) in commercial orchards in South Africa near Ladismith and Malmesbury in 2011. Postharvest fruit rot was identified from an orchard near Malmesbury in 2011. Affected fruit decayed after 2 months storage (5 to 7°C) and was covered with globose brown pycnidia (mean length × width: 113 × 102 μm; diameter range 72 to 149 μm; 40 spores). Fungal cultures isolated from fruit and shoot symptoms were morphologically identified as Coniella granati Sacc. Petrak and Sydow (synonym Pilidiella granati Saccardo; Alvarez et al. 2016). Hyphae were septate with hyaline, one-celled, ellipsoid to fusiform conidia (10.15 to 14.39 × 2.67 to 4.42 μm; average of 20 spores: 11.35 × 3.28 μm). Sequence data of the translation elongation factor alpha gene (TEF1, MG255164) and internal transcribed spacer region (ITS1-5.8S-ITS2; GenBank accession nos. KU666470 and KU666471) confirmed identifications with 99 to 100% similarity to reference sequences KX833681 and JN815313. Two-year-old pomegranate trees (cultivar Wonderful) were used to perform Koch’s postulates to verify that stem lesions were caused by isolates STE-U 7688 and STE-U 7689 (six trees per isolate). Six trees were used as a negative control. The place of inoculation on the main stem of the trees was surface sterilized (70% ethanol), wounded, and inoculated using a 5 mm mycelial plug, or a sterile PDA plug as a noninoculated control. The inoculated wound was covered with Parafilm and incubated for 3 months in a glasshouse at approximately 25°C. Dark brown lesions formed beneath the bark at the inoculation site, with mean lesion lengths 67 and 59 mm for STE-U 7688 and STE-U 7689, respectively. The control plants did not have lesions. Reisolation from the edge of the lesion confirmed the pathogenicity of the tested isolates. Pathogenicity was also tested on 20 surface-sterilized (0.5% sodium hypochlorite) wounded fruit (cultivar Wonderful) per isolate. Agar plugs (5 mm diameter) from the margin of PDA cultures (STE-U 7687, STE-U 7688, and STE-U 7689) were inserted into wounds and sealed using petroleum jelly. Fruit was incubated at 22 to 25°C in humidity chambers (85 to 95%) in the dark for 10 days. Extensive decay was consistently observed on inoculated fruit (mean lesion diameter 45 mm), and reisolation completed Koch’s postulates. Control fruit showed no decay. Cultures were stored in the Stellenbosch University Plant Pathology Department’s culture collection. C. granati has been reported on pomegranate previously from Asia (Mirabolfathy et al. 2012), Europe (Palou et al. 2010), and the United States (KC and Vallad 2016). However, to our knowledge, this is the first report of C. granati causing dieback and fruit rot of pomegranate in South Africa. This finding potentially impacts on the South African pomegranate industry owing to postharvest decay.
Agid:
6139935