First Report of Postharvest Fruit Rot Caused by Aspergillus ochraceus on Blue Honeysuckle (Lonicera caerulea L.) Fruit in China.

Abstract

Blue honeysuckle (Lonicera caerulea L.) plants produce small fruit that are used as food and medicine. In September 2024, 100 kg of blue honeysuckle 'Lanjingling' (China National Plant Variety Protection (CNPVP) 20200389) fruits were harvested in Harbin, China (126.48°E, 45.87°N), and 20% of the fruits showed postharvest fruit rot symptoms, leading to whole-fruit rotting with skin browning and necrotic lesions (Fig. 1. A). Small (1 to 2 mm) samples of infected tissue were obtained from five randomly selected fruits. Samples were surface sterilized with 75% ethanol for 30 s and 5% sodium hypochlorite (NaClO) for 3 min, rinsed three times with sterile distilled water, dried with paper towel, and plated on 9 cm Petri dishes containing potato dextrose agar (PDA). Purified cultures were obtained using the single-spore technique. After 5 d at 28°C, the colonies displayed yellow brown aerial mycelium on the PDA plates (Fig. 1. B, C). Conidiophores were transparent and smooth, while conidial heads were brown and nearly spherical (Fig. 1. D). The entire surface was fertile, producing mostly spherical to subglobose conidia with diameters of 2.12 to 3.24 μm (n = 50) (Fig. 1. E). The internal transcribed spacer region (ITS, included ITS1+5.8S +ITS2, GenBank PQ606583), β-tubulin (TUB, GenBank PQ611757), and nuclear large subunit rRNA (LSU, GenBank PQ620103) genes were partially amplified with their respective primers (ITS1/ITS4 (White et al. 1990), Btub2Fd/Btub4Rd (Glass and Donaldson, 1995) and LROR/LR7 (Rehner and Samuels, 1994). BLAST analysis revealed that the sequences of the three genes showed 99.30 to 100% homology (526/526 nt, 141/142 nt, and 882/882 nt) with the MH859926, AY819971, and MH876373 sequences for isolates of Aspergillus ochraceus. In a phylogenetic tree constructed by Maximum likelihood method based on ITS and TUB sequences, the isolate LDGS-6 was located in the same clade with A. ochraceus (Fig. 2). For pathogenicity, twenty healthy blue honeysuckle 'Lanjingling' fruits were superficially sterilized with 75% ethanol and washed with distilled water. Ten fruits were inoculated with a 10 μL conidial suspension of isolate LDGS-6 (106 spores/mL) and ten with sterile distilled water (control). After fruits were incubated in 9 cm Petri dishes at 28°C and 75% relative humidity in the dark for 7 d, inoculated fruits displayed rot symptoms while control fruits did not (Fig. 1. F and G). The experiment was replicated three times. The causal agent was isolated from inoculated fruits, and it was identified as the original isolate based on morphological traits and ITS, TUB, and LSU sequencing, whereas no Aspergillus-like strains were isolated from control fruits, thus confirming Koch's postulates. In conclusion, based on molecular, morphological, and pathogenic analysis, A. ochraceus is the causal agent of the fruit rot disease on blue honeysuckle fruits (Ou et al. 2024). A. ochraceus was previously reported in China in Shengzhou nane (on Prunus salicina var. taoxingli) (Ou et al. 2024). To our knowledge, this is the first report of postharvest fruit rot caused by A. ochraceus on blue honeysuckle fruits in China. The annual fruit yield production of trees over 5 years old can reach about 40,000 tons during the high-yielding years in China (Sun et al. 2024), but its storage is challenged by pathogen infection. Future work should focus on monitoring its occurrence and spread and developing effective control strategies.