First Report of Nothophoma spiraeae Causing Fruit Rot on Prunus armeniaca in China

Abstract

Apricot (Prunus armeniaca L.) is an important fruit crop produced worldwide and is widely cultivated in China (Guo et al. 2010). In July 2025, a severe fruit rot disease was observed on apricot trees in an orchard located in Harbin, Heilongjiang Province (126.68°E, 45.72°N). Based on a random survey of 30 plants, the incidence of the disease was estimated to be 32%. At the initial stage of pathogen infection, dark brown lesions appeared on the fruit surface, accompanied by a grayish-brown floccose mycelial layer. As the disease progressed, the pathogen invaded the fruit interior, causing browning and softening of the flesh and hindering fruit ripening. The entire fruit eventually rotted and completely dehydrated, forming dark brown mummified fruits that remained attached to the branches. Tissues from lesion margins were surface-disinfested, plated on potato dextrose agar (PDA), and incubated at 25°C in the dark. Hyphal tips were subcultured for purification and eleven isolates were obtained. Based on morphological observation and ITS sequencing, all eleven isolates were preliminarily identified as Nothophoma sp. Representative isolates (strains PN2 and PN7) were selected for pathogenicity tests. Seven-day-old mycelial plugs from the colony margins were used as inoculum to inoculate healthy apricot fruits attached to branches, with blank PDA plugs serving as controls. The fruits were surface-disinfested with 75% ethanol and subjected to two inoculation methods: wounded (punctured 8–10 times with a sterilized insect needle) and non-wounded. Apricot fruits wound-inoculated with strains PN2 and PN7 exhibited typical disease symptoms consistent with those observed in the field. Pure cultures with morphological and cultural characteristics identical to the original inoculated strains were reisolated from the lesion margins of symptomatic fruits. Conidia of strains PN2 and PN7 were ovoid to ellipsoid, smooth, aseptate, hyaline to olivaceous, and measured 5.3–7.1 × 3.7–4.4 μm. On PDA, colonies initially grew radially, with a pale yellowish-brown center and white cottony margins; the texture was dense in the center and sparse at the edge. Colony color later deepened to dark brown, becoming a dense, thick, cottony mat, with both color and texture showing obvious maturation. These characteristics were consistent with previous descriptions of Nothophoma spiraeae (Zhang et al. 2020). PCR amplification of genomic DNA of the two strains was performed for the nuclear ribosomal Internal Transcribed Spacer (ITS), Large Subunit Ribosomal (LSU), β-tubulin (TUB), and RNA polymerase II second largest subunit (RPB2) gene regions using primer pairs ITS1/ITS4 (White et al. 1990), LR0R/LR7 (Vilgalys et al. 1990), Bt2a/Bt2b (Glass et al. 1995), and RPB2-5F2/RPB2-7cr (Liu et al. 1999), respectively. The amplified products were sequenced, and eight high-quality sequences were obtained. All sequences were deposited in GenBank (ITS, PZ263778 and PZ263779; LSU, PZ263776 and PZ263777; TUB, PZ334562 and PZ334563; and RPB2, PZ334561 and PZ307118). BLAST homology analysis showed more than 99.6% identity with N. spiraeae and its closely related species Nothophoma quercina. Phylogenetic analysis revealed that strains PN2 and PN7 clustered with N. spiraeae. Nevertheless, N. spiraeae and N. quercina cannot be clearly separated using the selected molecular markers owing to insufficient phylogenetic resolution between these two species. Combining the phylogenetic data and morphological characteristics obtained in this study, the pathogen was tentatively identified as N. spiraeae. To the best of our knowledge, this is the first report of N. spiraeae causing fruit rot on P. armeniaca. This study supports prediction and management of this new apricot disease to lower economic losses in apricot production.