Successive effects of freeze–thaw cycles (FTCs) on soil respiration rate (Rs) were explored in a Korean Larch (Larix olgensis Herry.) plantation during the winter to spring season. In March 2014, laboratory incubation with severe FTCs at the extreme minimum temperatures of −16°C and mild FTCs (−8°C) and field-based methods through five days continuous measurements of Rs at eight time points in one day were applied to determine the diurnal and seasonal Rs variations during FTCs, and to analyze the effects of FTCs regimes on Rs. The Rs increased rapidly as thawing proceeded, generating two peaks during severe FTCs, but with no obvious CO₂ peaks in mild FTCs or field-based measurements. In severe FTCs, the Rs in first three FTCs changed dramatically, subsequently tended to stabilize. The diurnal Rs dynamics both followed unimodal type, with no fixed peak in laboratory study but the maximum value at 14:00 in field study. Laboratory- and field-based FTCs studies both highlighted the significant effects on soil carbon release. Initial response of soil respiratory bursts during early FTCs appeared to be driven by extreme minimum temperatures, while response of soil carbon release in late cycles was controlled by reduction in soil organic matter during early cycles.

Aralia elata (Miq.) Seem., is grown for its medicinal and nutritional properties in northeastern China. The tender shoots are used as wild vegetables. The plant saponin components have antioxidant and neuroprotective activities, and are used for the treatment of chronic disease (Xia et al. 2021). In July 2021, root rot disease was observed in five-year-old A. elata plants in Qingyuan County (41°91' N, 124°59' E), Liaoning Province, China. The incidence of roots rot was approximately 50% in old fields, with the leaves of the infected plants appearing chlorotic and wilting. The lesions on the taproots were dark brown and soft, with degraded internal organization. Leading edge of necrotic tissue from symptomatic roots was cut 5×5×3 mm, placed in 75% ethanol for 30 s, and then in 3% sodium hypochlorite for 2 min. After three rinses in sterile distilled water, the samples were dried on sterile filter paper before plating on potato dextrose agar (PDA) and incubation at 25℃. Monosporic cultures were obtained by the collection of single spores from individual isolates. After 7 days on PDA, mycelia in the colonies appeared cottony and pink, white, or purple in color, while their undersides were pink and white. Spore characteristics were evaluated after transfer to carnation leaf agar (CLA) and incubation for 20 days (Zhang et al. 2021). The macroconidia were falciform, slightly curved or straight, two to five septate, and 20.57 to 33.75 × 3.62 to 6.11 μm (n=40). The microconidia were ovoid or oval, zero to one septate, and 5.12 to 13.53 × 3.04 to 4.79 μm (n=40). Chlamydospores were globose to subglobose, intercalary or terminal, with an average diameter of 13.76 μm (n=40).To identify the pathogen, the internal transcribed spacer (ITS) region, large subunit (LSU) ribosomal DNA, and translation elongation factor 1 alpha (TEF-1α) gene were amplified using the respective primer pairs ITS1/ITS4, LR0R/LR7, and EF1-728F/EF1-986R (Cheng et al. 2020; Fu et al. 2019). Comparisons with GenBank, the sequences of ITS, LSU, and TEF-1 had 99 to 100% homology with Fusarium oxysporum (accessions numbers- MH707084, OQ380519, and GU250609, respectively). The sequences were deposited in GenBank: OP482273 (ITS), OP491955 (LSU), and OP503498 (TEF-1α). Maximum likelihood phylogeny of the identified sequences using MEGA-X software indicated that the isolate represented F. oxysporum. The taproots of 30 one-year-old A. elata were washed and inoculated with 1×106/ml of the conidial suspension for two hours, and another 30 used as controls with sterile water. After planting in sterilized forest soil in flowerpots (36×30 cm), the plants were grown in a greenhouse for two weeks at 25℃ with 14 h of light. It was found that 50% of the roots showed typical root rot symptoms, while the controls were asymptomatic. The pathogenicity test was repeated three times, and reisolation of F. oxysporum from the roots fulfilled Koch's postulates. This is the first report of root rot in A. elata caused by F. oxysporum in China and indicates the necessity for suitable management strategies to protect A. elata production. References: Cheng, Y., et al. 2020. Plant Dis. 104:3072. Fu, R., et al. 2019. Plant Dis. 103:1426. Xia, W., et al. 2021. Mini-Rev Med Chem. 21:2567. Zhang, X. M., et al. 2021. Plant Dis. 105:1223.

Aralia elata (Miq.) Seem, is an important cash crop in northeastern China. The tender shoots are rich in amino acids, vitamins, and trace elements, and the saponins of leaves and roots have antioxidant and immune-boosting properties. In August of 2023, root rot disease was observed in 4-year-old A. elata plants in Dongzhou County (41.79 °N, 124.11 °E), Liaoning Province, China, with an overall incidence of approximately 40%. While previous studies have described root rot in A. elata caused by Fusarium oxysporum (Zheng et al. 2024), this new root rot showed different symptoms. The leaves of the diseased plants were water-soaked and wilted but not chlorotic. The internal tissue of the roots was disintegrated and soft, while the xylem appeared brown and empty with only the epidermis remaining. Diseased root tissues were sterilized with 75% ethanol for 30 s, treated with 2% sodium hypochlorite for 2 min, and rinsed twice in sterile distilled water. Twelve isolates with similar morphological characteristics were obtained (isolation frequency of 80%), the isolates were plated on PDA medium and incubated at 25℃. Single-zoospore cultures were obtained and transferred to soybean agar medium (SA). After growth on SA for 7 days, the formation of rounded colonies of white aerial mycelia was observed. The sporangia were ovoid or ellipsoid, papillate, terminally borne, with an average length and width of 30.24 (18.35 to 45.39) × 24.16 (14.55 to 37.64) μm. The isolates were homothallic, produced plerotic oogonia with smooth walls with an average diameter of 27.97 (21.06 to 35.90 μm), and yielded one paragynous or anohiginous antheridium, sized 12.21 (10.11 to 14.72) μm × 9.75 (8.39 to 11.31) μm. Based on these morphological characteristics, the isolates were identified as part of the Phytophthora genus (Montealegre et al. 2016). The internal transcribed spacer (ITS) region and cytochrome oxidase subunit Ⅱ (COXⅡ) gene were amplified using the respective primers ITS1/ITS4 and FM66/FM58 (Wiseman et al. 2018). The ITS and COXⅡ sequences were compared with sequences in GenBank, showing 99.83% to 100% sequence identity with Phytophthora cactorum (accession nos. OR347848 and OR351295, respectively). The sequences have been deposited in GenBank with the accession numbers PP479774 (ITS) and PP489221 (COXⅡ). Construction of a maximum-likelihood phylogenetic tree of the identified sequences using MEGA-X indicated that the isolate could be identified as P. cactorum. To confirm pathogenicity, shallow wounds were made in the taproots of 10 one-year-old A. elata and were inoculated with four 9-mm diameter agar plugs from one-week-old oomycete cultures on SA agar per root, and the pathogenicity test was repeated twice. Another 10 wounded plants inoculated with agar plugs without oomycete served as the controls. The plants were planted in flowerpots filled with sterilized forest soil and cultured in a greenhouse at 25℃ with 14 h of light per day. After 20 days, the inoculated plants showed similar symptoms to those initially observed in the field. No symptoms of root rot were observed in the controls. The P. cactorum was re-isolated from the inoculated plants, and identified based on the morphology and ITS and COXⅡ sequence, fulfilling Koch's postulates. P. cactorum has been reported to cause root rot in A. elata in Korea and Japan (Lee et al. 2005; Uchida et al. 1984). To our knowledge, this is the first report of P. cactorum causing root rot in A. elata in China. P. cactorum is a serious threat to A. elata cultivation, and disease management strategies need to be developed.