Alternaria alternata is the main pathogenic species of various crops, including kiwifruit (Actinidia cinensis). In this study, an antagonistic fungus, J-1, with high antifungal activity against A. alternata was isolated from A. cinensis “Hongyang.” The strain J-1 was identified as Fusicolla violacea via morphological identification and DNA sequencing. This study aimed to evaluate the antifungal activity and potential mechanism of the strain J-1 against A. alternata. The strain J-1 exhibited antifungal activity against A. alternata, with an inhibition rate of 66.1% in vitro. Aseptic filtrate (AF) produced by the strain J-1 could suppress the mycelial growth and conidia germination of A. alternata at the inhibition rates of 66.8% and 80%, respectively, as well as suppress the spread of Alternaria rot in fresh kiwifruit. We observed that many clusters of spherical protrusions appeared at the mycelial tips of A. alternata after treatment with 200 mL L⁻¹ AF of J-1. Scanning electron microscopy analysis results showed that the mycelial structures were bent and/or malformed and the surfaces were rough and protuberant. Variations in temperature, pH, and storage time had little effect on the antifungal activity of the AF. Moreover, the AF could damage the integrity of cell membranes and cause intracellular content leakage. Meanwhile, the chitinase and β-1,3-glucanase enzyme activities increased significantly, indicating that the function of A. alternata cell wall was seriously injured. Eleven antimicrobial metabolites were identified by gas chromatography–mass spectrometry (GC–MS). The strain J-I and its AF exhibited well broad-spectrum antifungal activity against Diaporthe eres, Epicoccum sorghinum, Fusarium graminearum, Phomopsis sp., and Botryosphaeria dothidea, with inhibition rates ranging from 34.4% to 75.1% and 42.7% to 75.2%, respectively. Fusicolla violacea J-1 is a potential biocontrol agent against A. alternata and other fungal phytopathogens.

Kiwifruit (Actinidia chinensis) is an important commercial crop in China, and the occurrence of diseases may cause significant economic loss in its production. In the present study, a new pathogen that causes brown leaf spot disease on kiwifruit was reported. The fungus was isolated from an infected sample and identified as Fusarium graminearum based on morphological and molecular evaluation. Koch’s postulates were confirmed when the pathogen was re-isolated from plants with artificially induced symptoms and identified as F. graminearum. Based on the biological characteristics of the pathogen, it was determined that: its optimal growth temperature was 25 °C; optimal pH was 7; most suitable carbon source was soluble starch; most suitable nitrogen source was yeast powder; and best photoperiod was 12 h light/12 h dark. Further investigations were conducted by determining 50% effective concentrations (EC₅₀) of several active ingredients of biological fungicides against F. graminearum. The results showed that among the studied fungicides, tetramycin and honokiol had the highest antifungal activity against this pathogen. Our findings provide a scientific basis for the prevention and treatment of brown leaf spot disease on kiwifruit.

‘Hongyang’ kiwifruit (Actinidia chinensis, cultivar ‘Hongyang’) black spot disease is caused by the fungal pathogen Didymella glomerata, and is a serious disease, causing considerable losses to the kiwifruit industry during growth of the fruit. Hence, we aimed to identify a potential biocontrol agent against D. glomerata. In this study, bacterial isolates from the rhizosphere soil of kiwifruit were tested for their potential antifungal activity against selected fungal pathogens. Based on a phylogenetic tree constructed using sequences of 16S rDNA and the gyrA gene, BQ-33 with the best antifungal activity was identified as Bacillus mojavensis. We evaluated the antagonistic activity and inhibitory mechanism of BQ-33 against D. glomerata. Confrontation experiments showed that both BQ-33 suspension and the sterile supernatant (SS) produced by BQ-33 possessed excellent broad-spectrum antifungal activity. Furthermore, the SS damaged the cell membrane and cell wall of the mycelia, resulting in the leakage of a large quantity of small ions (Na⁺, K⁺), soluble proteins and nucleic acids. Chitinase and β-1,3-glucanase activities in SS increased in correlation with incubation time and remained at a high level for several days. An in vivo control efficacy assay indicated that 400 mL L⁻¹ of SS completely inhibited kiwifruit black spot disease caused by D. glomerata. Therefore, BQ-33 is a potential biocontrol agent against kiwifruit black spot and plant diseases caused by other fungal pathogens. To our knowledge, this is the first report of the use of a rhizosphere microorganism as a biocontrol agent against kiwifruit black spot disease caused by D. glomerata.

Passion fruit (Passiflora edulis) is a tropical and subtropical plant that is widely cultivated in China due to its high nutritional value, unique flavor and medicinal properties. In August 2020, typical anthracnose symptoms with light brown and water-soaked lesions on Passiflora edulis Sims were observed, which result in severe economic losses. The incidence of this disease was approximately 30%. The pathogens from the infected fruit were isolated and purified by the method of tissue isolation. Morphological observations showed that the colony of isolate BXG-2 was gray to celadon and grew in concentric circles. The orange conidia appeared in the center after 14 days of incubation. The pathogenicity was verified by Koch’s postulates. The internal transcribed spacer (ITS), chitin synthase (CHS-1), actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were amplified by relevant PCR programs. The multi-gene (ITS, GAPDH, ACT, CHS-1) phylogeny analysis confirmed that isolate BXG-2 belongs to Colletotrichum fructicola. The inhibitory effect of six synthetic fungicides on the mycelial growth of the pathogen was investigated, among which difenoconazole 10% WG showed the best inhibitory effect against C. fructicola with an EC₅₀ value of 0.5579 mg·L⁻¹. This is the first report of anthracnose on Passiflora edulis Sims caused by Colletotrichum fructicola in China.

Kiwifruit is a nutritious and economically important fruit that is widely cultivated in China. In 2021, leaf spot disease of kiwifruit was discovered in the main kiwifruit-producing area of Xifeng County, Guizhou Province, China. Leaf spot disease weakens plant photosynthesis and reduces nutrient synthesis, thereby affecting plant growth. We studied the morphological characteristics and performed a combined analysis of EF-1α, RPB2, and TUB2 genes of Fusarium fujikuroi, a fungus associated with leaf spot disease. The pathogenicity of F. fujikuroi followed Koch’s hypothesis, confirming that this fungus is the cause of kiwifruit leaf spot disease. The sensitivity of seven natural antifungal agents against F. fujikuroi was measured using the mycelial growth rate method. Honokiol, cinnamaldehyde, and osthol showed good antifungal effects against F. fujikuroi, with EC₅₀ values of 18.50, 64.60, and 64.86 μg/mL, respectively. The regression coefficient of cinnamaldehyde was the largest at 2.23, while that of honokiol was the smallest at 0.408. Fusarium fujikuroi was the most sensitive to cinnamaldehyde.

Soft rot disease caused by Botryosphaeria dothidea and Phomopsis sp. is the most serious fungal disease of the kiwifruit production area in southwest China. In this work, the role of the co-application of tetramycin and matrine in the resistance of kiwifruit fruits against soft rot disease and its effects on development, quality and amino acids of kiwifruit fruits were investigated. The results indicate that matrine exhibited an outstanding toxicity against B. dothidea RF-1 and Phomopsis sp. RF-2 with EC₅₀ values of 0.442 and 0.332 mg kg⁻¹. The foliar co-application of 0.3% tetramycin aqueous solutions (AS) 5000-fold liquid + 0.5% matrine AS 1000-fold liquid could effectively control soft rot disease with a control efficacy of 82.68%, which was significantly (p < 0.05) higher than 75.19% of 0.3% tetramycin AS 5000-fold liquid and significantly (p < 0.01) higher than 68.50% of 0.5% matrine AS 500-fold liquid. Moreover, the co-application of tetramycin and matrine was more effective than tetramycin or matrine alone in improving disease resistance, quality and amino acids of kiwifruit fruits. This study highlights that the co-application of tetramycin and matrine can be used as a practicable, cost-effective and environmentally friendly candidate or alternative approach for controlling soft rot disease of kiwifruit.