Fusarium wilt of banana (Musa spp.) caused by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc) is a typical soilborne disease, that severely devastates the banana industry worldwide, and soil microbial diversity is closely related to the spread of Fusarium wilt. To understand the relationship between microbial species and Fusarium wilt, it is important to understand the microbial diversity of the Fusarium wilt-diseased and disease-free soils from banana fields. Based on sequencing analysis of the bacterial 16S rRNA genes and fungal internal transcribed spacer (ITS) sequences, Foc abundance, fungal or bacterial richness and diversity were higher in the diseased soils than in the disease-free soils. Although Ascomycota and Zygomycota were the most abundant fungi phyla in all soil samples, Ascomycota abundance was significantly reduced in the disease-free soils. Mortierella (36.64%) was predominant in the disease-free soils. Regarding bacterial phyla, Proteobacteria, Acidobacteria, Chloroflexi, Firmicutes, Actinobacteria, Gemmatimonadetes, Bacteroidetes, Nitrospirae, Verrucomicrobia and Planctomycetes were dominant phyla in all soil samples. In particular, Firmicutes contributed 16.20% of the total abundance of disease-free soils. At the bacterial genus level, Bacillus, Lactococcus and Pseudomonas were abundant in disease-free soils with abundances of 8.20, 5.81 and 2.71%, respectively; lower abundances, of 4.12, 2.35 and 1.36%, respectively, were found in diseased soils. The distribution characteristics of fungal and bacterial genera may contribute to the abundance decrease of Foc in the disease-free soils. Unique distributions of bacteria and fungi were observed in the diseased and disease-free soil samples from banana fields. These specific genera are useful for constructing a healthy microbial community structure of soil.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is one of the most destructive banana diseases in the world, which limits the development of the banana industry. Compared with traditional physical and chemical practices, biological control becomes a promising safe and efficient strategy. In this study, strain Y1-14 with strong antagonistic activity against Foc TR4 was isolated from the rhizosphere soil of a banana plantation, where no disease symptom was detected for more than ten years. The strain was identified as Streptomyces according to the morphological, physiological, and biochemical characteristics and the phylogenetic tree of 16S rRNA. Streptomyces sp. Y1-14 also showed a broad-spectrum antifungal activity against the selected 12 plant pathogenic fungi. Its extracts inhibited the growth and spore germination of Foc TR4 by destroying the integrity of the cell membrane and the ultrastructure of mycelia. Twenty-three compounds were identified by gas chromatography–mass spectrometry (GC-MS). The antifungal mechanism was investigated further by metabolomic analysis. Strain Y1-14 extracts significantly affect the carbohydrate metabolism pathway of Foc TR4 by disrupting energy metabolism.

Nitrogen is a crucial element for the growth and development of plants, directly affecting crop growth and yield. To investigate the physiological and molecular mechanism of nitrogen-deficiency stress, we conducted an investigation into the effects of different nitrogen levels on the growth, photosynthetic characteristics, and gene transcription levels of banana seedlings. Compared with the control group with normal nitrogen levels (NN), the height of plants receiving Reduced-N (NR), Low-N (LN), and N-Free (NF) treatments was decreased by 0.45 cm, 2.5 cm, and 3.25 cm, respectively. Their dry weight was reduced by 1.63 g, 2.99 g, and 2.88 g, respectively. Conversely, the dry weight of the underground plant part in the LN and NF treatment groups exhibited an increase of 0.13 g and 0.16 g, respectively. Regarding photosynthetic characteristics, the Specialty Products Agricultural Division (SPAD) values of the NR, LN, and NF treatments showed reductions of 15.5%, 30.4%, and 35.9%, respectively, compared with those of the control treatments. The values of maximum photosynthetic efficiency (Fv/Fm), actual photosynthetic efficiency (Y(Ⅱ)), and relative electron transfer (ETR) of the banana seedlings decreased to different degrees after NR, LN, and NF treatment, and their values were positively correlated with N levels. Gene transcription analysis showed that N transport-related proteins, including NRT1.7, NRT2.3a, NRT2.3b, and NRT2.5, were significantly up-regulated to increase the nitrogen absorption capacity of plant roots. On the other hand, various transcription factors including GRAS, MYB, and WRKY were notably up-regulated, facilitating root growth and the expanding root absorption area, thereby enhancing nitrogen uptake. Furthermore, genes associated with endogenous hormone metabolic pathways such as gibberellin (GA), strigolactone (SL), and brassinosteroids (BR) were activated in banana plants subjected to low nitrogen stress, enhancing the plant’s ability to adapt to nitrogen-deficient conditions. These findings offer valuable insights into understanding the transcriptional regulatory mechanisms governing banana responses to low nitrogen stress and breeding new varieties with improved nutrient utilization.

Banana wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is a devastating fungal disease. Biocontrol strategies hold immense potential for inhibiting the spread of Foc TR4. Here, 30 actinobacteria were isolated from soils and screened for their antagonistic activity against Foc TR4. Strain SCA4-21^T was selected due to its strongest antagonistic activity against Foc TR4. Strain SCA4-21^T also exhibited strong antagonistic activity against the other eight phytopathogenic fungi. The strain was identified as the genus Streptomyces according to its physiological, biochemical, and phenotypic characteristics. The phylogenetic trees of 16S rRNA sequences demonstrated that strain SCA4-21^T formed a subclade with S. iranensis HM 35^T and/or S. rapamycinicus NRRL B-5491^T with low bootstrap values. Considering that 16S rRNAs did not provide sufficient resolution for species-level identification, the whole genome of strain SCA4-21^T was sequenced. Multilocus sequence analysis (MLSA) based on five housekeeping gene alleles (atpD, gyrB, recA, rpoB, and trpB) revealed that strain SCA4-21^T clustered into S. hygroscopicus subsp. hygroscopicus NBRC 13472^T with 100% of bootstrap value. The analysis of the genome-based phylogeny also approved the results. Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) were 91.26 and 44.30%, respectively, with values below the respective species level threshold of 95 and 70%. Hence, strain SCA 4–21^T represented a novel species within the genus Streptomyces, named Streptomyces luomodiensis sp. nov. The type strain is SCA4-21^T (=GDMCC4.340^T = JCM36555^T). By the CAZymes analysis, 348 carbohydrate-active enzymes (CAZymes) were detected, including 15 chitinases and eight β-1,3-glucanases. The fermentation broth of strain SCA4-21^T, exhibiting strong antagonistic activity against Foc TR4, demonstrated high activities of chitinase and β-1,3-glucanase, which might be involved in antifungal activity. Our results showed an innovative potential biocontrol agent for managing plant fungal diseases, specifically banana fusarium wilt.

The soil-borne fungus Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes banana Fusarium wilt, a serious threat to global banana production. Biocontrol represents a promising alternative to conventional chemical control for managing this disease. Our previous studies identified Streptomyces luomodiensis SCA4-21 as a novel species with antifungal properties. Here, we show that the extract from strain SCA4-21 significantly inhibits Foc TR4 mycelial growth and spore germination, severely disrupting hyphal and spore ultrastructure. The extract also exhibited broad-spectrum activity against eight other phytopathogenic fungi. We identified 32 volatile organic compounds produced by strain SCA4-21, including five with known antifungal properties. In pot experiments, strain SCA4-21 inoculation not only significantly suppressed Foc TR4 infection in banana seedlings, with a biocontrol efficacy of 59.3%, but also markedly promoted plant growth. The inoculation significantly enriched beneficial bacterial genera ( Streptomyces , Bacillus , Sphingomonas , Massilia , and Pseudomonas ) and fungal genera ( Mortierella , Gibellulopsis , and Xenomyrothecium ), while reducing the pathogenic bacterium Pantoea and lowering Fusarium abundance to levels statistically indistinguishable from the control. Microbial function prediction based on 16S rRNA gene sequencing data revealed enhanced metabolic pathways, including carbohydrate metabolism, amino acid metabolism, and metabolism of terpenoids and polyketides. We propose that strain SCA4-21 combats banana Fusarium wilt through a synergistic mechanism involving antifungal compound production and recruitment of beneficial microbiota. These findings highlight strain SCA4-21 as a promising biocontrol agent for sustainable banana production. IMPORTANCE: Banana ( Musa spp.) is one of the most popular fruit crops and the fourth largest food crop in developing countries within tropical and subtropical regions. However, the emergence and rapid spread of strain Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) seriously hinder the development of the banana industry. Currently, there is no effective control measure available. Biological control holds potential due to its safety and effectiveness. Here, we found that the extract of Streptomyces luomodiensis SCA4-21 exhibited significant inhibitory effects on the hyphal growth and spore germination of Foc TR4, as well as severe destructive effects on its cell morphology and ultrastructure, and broad-spectrum antifungal activity. We also discovered that the inoculation of strain SCA4-21 significantly inhibited the infection of Foc TR4 in banana seedling corms, reduced the incidence index of banana Fusarium wilt, promoted the growth of banana seedlings, and enhanced beneficial microbes and metabolic pathways, suggesting that strain SCA4-21 is a promising biocontrol agent.