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First Report of Diplodia seriata Causing Loquat Fruit Rot in Spain

Palou, L., Taberner, V., Montesinos-Herrero, C.
Plant disease 2013 v.97 no.3 pp. 421
DNA primers, Diplodia, Eriobotrya japonica, Vitis, agar, alcohols, blight, conidia, cultivars, cutting, dieback, fruit trees, fruits, fungi, genes, internal transcribed spacers, loquats, malt extract, mycelium, olives, orchards, pathogens, plant pathology, plant rots, planting, polymerase chain reaction, pycnidia, ribosomal DNA, surveys, vines, Spain
Spain is the second largest loquat (Eriobotrya japonica Lindl.) producer in the world, with about 40,000 t per year. ‘Algerie’ is the main cultivar planted in Alicante province (SE of Spain; Lat. 38.40° N, Long. 0.08° W), where more than 80% of Spanish commercial loquat plantations are located. In a survey of fruit losses at harvest, irregular brownish superficial dry spots (5 to 15 mm) located mainly near the stem end were observed on fruits from different orchards. After incubation at 20°C for 14 days, the spots on fruit expanded rapidly and turned to dark brown or black, producing black, unilocular, ostiolate, and thick-walled pycnidia. Isolation was performed by disinfecting the surface of symptomatic fruits with alcohol and aseptically cutting pieces of infected peel tissue and plating them in potato dextrose agar (PDA) dishes. The potential causal agent (isolate IVIA GCA-5) was identified in the Spanish Type Culture Collection (CECT, University of Valencia, Valencia, Spain). The fungus grew rapidly on both PDA and malt extract agar (MEA) at 26°C, covering the entire plate surface with dark gray mycelium within 4 days. The plate reverse was dark gray to black. The conidia were brown and aseptate, with the apex broadly rounded and the base rounded or truncate, and 23 × 11 μm (n = 50). The identification of Diplodia seriata De Not. was molecularly confirmed with the amplification with the primers ITS1 and ITS4 and subsequent sequencing of the internal transcribed spacer ITS1-5.8S-ITS2 region of the rDNA extracted from the isolate IVIA GCA-5 (GenBank Accession No. JX987099). Furthermore, the region D1/D2 in the 5′ end of the 28S rDNA gene was amplified with the primers NL1 and NL4 and sequenced (JX997743). A nucleotide BLAST analysis showed in both cases 100% identity with D. seriata [EF127892 (3) and AY928050, respectively]. To fulfill Koch's postulates, 5-mm diameter mycelial plugs from 7-day-old colonies of isolate IVIA GCA-5 grown on PDA at 25°C were aseptically transferred to skin wounds on superficially disinfected ‘Algerie’ loquats (one plug per fruit; n = 9). Wounded but not inoculated fruit were used as controls. The experiment was repeated three times. Inoculated fruit developed lesions of 18 to 100 mm after 7 to 21 days of incubation at 20°C. No lesion was observed on controls. The fungus was consistently reisolated from inoculated fruit. D. seriata is a broadly spread pathogen causing cankers, blight, dieback, and fruit rots in vines and many fruit trees. In Spain, it has been reported to cause fruit rot of olive (1) and branch dieback in olive (2) and grapevine (4). To our knowledge, this is the first report worldwide of D. seriata causing loquat fruit rot.References: (1) J. Moral et al. Plant Dis. 92:311, 2008. (2) J. Moral et al. Phytopathology 100:1340, 2010. (3) A. J. L. Phillips et al. Fungal Divers. 25:141, 2007. (4) J. R. Úrbez-Torres et al. Plant Dis. 90:835, 2006.