First Report of Neofusicoccum parvum Causing Fruit Rot on Eriobotrya japonica in China

Abstract

Loquat, Eriobotrya japonica (Thunb.) Lindl., is one of the most economically important fruit trees in China. During 2017, a field survey conducted in orchards of the Fuling District, Chongqing City, revealed the occurrence of fruit rot of mature fruit of E. japonica ‘Dawuxing’. Water-soaked decay with a brown stripe around the lesion was present on symptomatic fruits. Tissues from symptomatic fruit (5 × 5 mm) were aseptically separated and surface disinfested in 2.5% sodium hypochlorite for 45 s, rinsed in sterile water, disinfested in 75% ethyl alcohol for 45 s, rinsed in sterile water twice for 30 s, placed onto potato dextrose agar (PDA), and incubated at 25°C in the dark for 3 days. Tissues from 30 out of 32 affected fruits developed fungal colonies. Seven of them showed a white mycelium, moderately dense, becoming dark gray after 5 days. Pycnidia of strain YLLO2-1a were produced on the surface of PDA after 50 days under a photoperiod of 12 h at 25°C. Conidia were hyaline, aseptate, ellipsoidal, measuring (12.4 to) 15.8 (to 19.4) × (4.5 to) 6.7 (to 9.4) μm. Based on morphological characteristics, strain YLLO2-1a was tentatively identified as Neofusicoccum sp. (Crous et al. 2006; Palavouzis et al. 2015; Slippers et al. 2004). Further species identification was performed by polymerase chain reaction and BLAST sequencing analyses of the partial internal transcribed spacer (ITS) rDNA region, β-tubulin (BT), and translation elongation factor 1 alpha (EF-1α) genes. Sequences of strain YLLO2-1a have been deposited in GenBank under accession numbers MH393618 (ITS region), MH393617 (BT gene), and MH824423 (EF-1α gene). BLAST searches of those sequences in GenBank showed >99% similarity with sequences of reference N. parvum isolate CMW9080 (ITS, accession no. AY236942; BT, accession no. AY236916; and EF-1α, accession no. AY236887). To confirm pathogenicity, mycelium plugs of a 3-day-old colony of strain YLLO2-1a were placed onto the surface of wounded and unwounded mature fruits (six replicates) of loquat ‘Dawuxing’. Wounded and unwounded but not inoculated fruits were used as controls. The experiment was repeated twice. Inoculated fruits were incubated at 25°C in plastic containers (42.0 × 31.0 × 12.0 cm) covered with plastic film. All inoculated fruits showed small necrosis spots at 24 h postinoculation (hpi). The rot lesions quickly expended into the entire fruit at approximately 96 hpi. Both inoculated wounded and unwounded fruits developed lesions of 5.75 ± 0.88 and 4.33 ± 0.25 cm² (average area ± SD) at 72 hpi, respectively, whereas the control fruits inoculated with noncolonized PDA plugs remained asymptomatic. The pathogen was reisolated from the lesions of inoculated fruits and confirmed to be N. parvum by morphological characterization and ITS sequence. Based on these results, N. parvum was determined as the pathogen responsible for the fruit rot disease on loquat. N. parvum is a broadly spread pathogen, causing cankers and dieback on loquat tree in Italy and Spain (Giambra et al. 2016; Gonzalez-Dominguez et al. 2017). However, shoots and branches infected with N. parvum were not found in our study. To our knowledge, this is the first report of N. parvum affecting loquat in China.