Blueberry is a shallow root plant in which the absorption of nutrients is inefficient, resulting in slow growth under artificial cultivation conditions. Endophytes play an important role in promoting plant growth; however, the effects of Trichoderma spp. and dark septate endophytes (DSEs) on host plant growth and soil microorganisms are still debatable. We isolated two endophytic fungal species, Trichoderma koningiopsis (TK) and a DSE (Amesia nigricolor AN), from blueberry roots, which can solubilize insoluble phosphorus and produce amylase and cellulase to promote plant growth. We found that under dual inoculation, the colonization rate and colonization intensity of TK were higher than they were under single inoculation with TK, while the colonization rate and colonization intensity of AN were lower under dual inoculation than under single inoculation with AN. The plant nutrients, root activity, available potassium, and parts of soil phosphatase activities were highest under dual inoculation. TK inoculation resulted in the highest diversity and richness in the soil fungi and bacteria, followed by dual inoculation. The abundance of Ascomycota, Acidobacteriae, Firmicutes, and Actinobacteriota increased significantly, resulting in Trichoderma and Vicinamibacteria inoculated with TK, Chaetomium and Alicyclobacillales inoculated with AN, and Hypocreales and Burkholderiaceae with dual inoculation enriched in the soil.

Since its publication, the authors of Xu et al. (2022) have identified errors in two of their figures. In Fig. 2(d), some of the images were inadvertently misplaced during assembly, and in Fig. 6, the scale bars were missing. The authors present their corrected figures below, and also provide whole blot images for the blots corrected in Fig. 2(d) in Supporting Information Notes S1. These errors in the represented figures do not affect the accuracy of the conclusions presented in the article.

Crown width (CW) is an important tree variable and is often used as a covariate predictor in forest growth models. The precise measurement and prediction of CW is therefore critical for forest management. In this study, we introduced tree species as a random effect to develop nonlinear mixed-effects CW models for individual trees in multi-species secondary forests, accounting for the effects of competition. We identified a simple power function for the basic CW model. In addition to diameter at breast height (DBH), other significant predictor variables including height to crown base (HCB), tree height (TH), and competition indices (CI) were selected for the mixed-effects CW model. The sum of relative DBH (SRD) was identified the optimal distance-independent CI and as a covariate predictor for spatially non-explicit CW models, whereas the sum of the Hegyi index for fixed number competitors (SHGN) was the optimal distance-dependent CI for spatially explicit CW models, with significant linear correlation (R2 = 0.943, P < 0.001). Both spatially non-explicit and spatially explicit mixed-effects CW models were developed for studied secondary forests. We found that these models can describe more than 50% of the variation in CW without significant residual trends. Spatially explicit models exhibited a significantly larger effect on CW than spatially non-explicit ones; however, spatially explicit models are computationally complex and difficult and can be replaced by corresponding spatially non-explicit models due to the small differences in the fit statistics. The models we present may be useful for forestry inventory practices and have the potential to aid the evaluation and management of secondary forests in the region.

In February 2017, an unknown root disease was observed on blueberry (Vaccinium uliginosum L.) plants in Fenggang county, Guizhou Province, China. Root symptoms began with small necrotic lesions; subsequently, dark brown rot of the tap root and stem base was observed; finally, the whole plant withered and died. Root tissue was obtained from the junction of diseased and healthy tissue, and the samples were rinsed 3 times with sterile water. Then the surface was disinfected in 75% alcohol for 30 s, washed three times with sterile water, washed with 3% (v/v) sodium hypochloride for 3 min, rinsed three times in sterile water and cultured on PDA at 28 ℃ for 3-5 days. Fungal colonies were subcultured on PDA 3-4 times until purified colonies were obtained. Eight isolates exhibiting morphological characteristics of Fusarium were recovered from symptomatic roots. Six isolates showed morphological characteristics consistent with Fusarium commune. The colonies of LMGF6, a representative, on PDA were white and pink, and there was abundant aerial hyphae. Microconidia were cylindrical, usually without septa, with a dimension of 5.0 to 12.0 μm × 2.0 to 3.5 μm; macroconidia were usually 3-septate and 10.5 µm to 36.5 µm × 3.0 to 5.0 μm in size. Chlamydospores were smooth and spherical. DNA fragments were amplified from LMGF1-6 from the internal transcribed spacer (ITS) region using ITS1/ITS4 primers (White et al. 1990), DNA-directed RNA polymerase II second largest subunit (RPB2) gene using 5f2/7cr primers and translation elongation factor 1-alpha (TEF1) gene using EF1/EF2 primers (Zhong et al. 2021; O’Donnell et al. 2022). The sequences were submitted to GenBank (GenBank accession Nos. OP035965 to OP035970 for ITS, OP106349 to OP106354 for RPB2, and OP106355 to OP106360 for TEF1). BLAST analysis showed 100% identity to those of F. commune. Ten plants were used for the experimental and control. The roots of experimental bushes were inoculated with 50 ml of a 1ⅹ106 conidial suspension. The roots of control plants were irrigated with sterile water. The plants were grown under the ambient conditions (monthly average maximum temperature of 30℃, monthly average minimum temperature of 20℃). After 25 days, all inoculated plants showed symptoms similar to those of the natural infection observed, but no lesions were observed on the control plants. The same fungus was successfully reisolated from all of the inoculated plants and was identified as F. commune based on colony morphology, phylogenetic analysis of concatenated ITS-RPB2-TEF1 sequences was performed using MEGA7.0 and pathogenicity tests. To our knowledge, this is the first report of F. commune causing root rot on blueberry plants in Guizhou Province, China.

Dark septate endophytes (DSEs) and Phosphate-solubilizing fungi (PSFs) are widely distributed and have important application value in improving plant growth. However, the effects of DSE fungi with phosphate-solubilizing ability on host plants need further study. In this study, phosphorus-dissolving DSE fungi were screened for growth-promoting effects. We isolated, identified and characterized three DSE fungal species (Thozetella neonivea, Pezicula ericae and Hyaloscyphaceae sp.) showing phosphate-solubilizing ability. The impact of three single or dual inoculations of DSEs on blueberry plant characteristics was studied. Their effects on colonization intensity, biomass in seedlings, nutrients in plants and soil, and activities of plant resistance enzymes and soil enzymes were remarkably upregulated relative to the control (p < 0.05). The available phosphorus and acid phosphatase in different combinations were significantly increased. These findings indicate that the application of three DSEs may be valuable to facilitate the cultivation of blueberry with a higher biomass and improved plant quality.