Intercropping can achieve sustainable agricultural development by increasing plant diversity. In this study, we investigated the effects of tomato monoculture and tomato/potato-onion intercropping systems on tomato seedling growth and changes of soil microbial communities in greenhouse conditions. Results showed that the intercropping with potato-onion increased tomato seedling biomass. Compared with monoculture system, the alpha diversity of soil bacterial and fungal communities, beta diversity and abundance of bacterial community were increased in the intercropping system. Nevertheless, the beta-diversity and abundance of fungal community had no difference between the intercropping and monoculture systems. The relative abundances of some taxa (i.e., Acidobacteria-Subgroup-6, Arthrobacter, Bacillus, Pseudomonas) and several OTUs with the potential to promote plant growth were increased, while the relative abundances of some potential plant pathogens (i.e., Cladosporium) were decreased in the intercropping system. Redundancy analysis indicated that bacterial community structure was significantly influenced by soil organic carbon and pH, the fungal community structure was related to changes in soil organic carbon and available phosphorus. Overall, our results suggested that the tomato/potato-onion intercropping system altered soil microbial communities and improved the soil environment, which may be the main factor in promoting tomato growth.

Sub-optimal temperatures can adversely affect tomato (Solanum lycopersicum) growth, and K⁺ plays an important role in the cold tolerance of plants. However, gene expression and K⁺ uptake in tomato in response to sub-optimal temperatures are still not very clear. To address these questions, one cold-tolerant tomato cultivar, Dongnong 722 (T722), and one cold-sensitive cultivar, Dongnong 708 (S708), were exposed to sub-optimal (15/10 °C) and normal temperatures (25/18 °C), and the differences in growth, K⁺ uptake characteristics and global gene expressions were investigated. The results showed that compared to S708, T722 exhibited lower reduction in plant growth rate, the whole plant K⁺ amount and K⁺ net uptake rate, and T722 also had higher peroxidase activity and lower K⁺ efflux rate under sub-optimal temperature conditions. RNA-seq analysis showed that a total of 1476 and 2188 differentially expressed genes (DEGs) responding to sub-optimal temperature were identified in S708 and T722 roots, respectively. Functional classification revealed that most DEGs were involved in “plant hormone signal transduction”, “phenylpropanoid biosynthesis”, “sulfur metabolism” and “cytochrome P450”. The genes that were significantly up-regulated only in T722 were involved in the “phenylpropanoid biosynthesis” and “plant hormone signal transduction” pathways. Moreover, we also found that sub-optimal temperature inhibited the expression of gene coding for K⁺ transporter SIHAK5 in both cultivars, but decreased the expression of gene coding for K⁺ channel AKT1 only in S708. Overall, our results revealed the cold response genes in tomato roots, and provided a foundation for further investigation of mechanism involved in K⁺ uptake in tomato under sub-optimal temperatures.

Introduction: Trichoderma spp. is a recognized bio-control agent that promotes plant growth and enhances resistance against soil-borne diseases, especially Fusarium wilt. It is frequently suggested that there is a relationship between resistance to melon wilt and changes in soil microbiome structures in the rhizosphere with plant metabolites. However, the exact mechanism remains unclear.Method: This study aims to investigate the effects of Trichoderma application on the metabolic pathway of oriental melon roots in response to Fusarium oxysporum f. sp. melonis in a pot experiment. The experiment consisted of three treatments, namely water-treated (CK), FOM-inoculated (KW), and Trichoderma-applied (MM) treatments, that lasted for 25 days. Ultra-performance liquid chromatography-electron spray ionization-mass spectrometry (UPLC-ESI-MS) was used to analyze the compounds in melon roots.Results: The results show that Trichoderma harzianum application resulted in a reduction in the severity of oriental melon Fusarium wilt. A total of 416 distinct metabolites, categorized into four groups, were detected among the 886 metabolites analyzed. Additionally, seven differential metabolites were identified as key compounds being accumulated after inoculation with Fusarium oxysporum f. sp. melonis (FOM) and Trichoderma. The mechanism by which Trichoderma enhanced melon's resistance to Fusarium wilt was primarily associated with glycolysis/gluconeogenesis, phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, and the biosynthesis of cofactors pathway. In comparison with the treatments of CK and MM, the KW treatment increased the metabolites of flavone and flavonol biosynthesis, suggesting that oriental melon defended against pathogen infection by increasing flavonol biosynthesis in the KW treatment, whereas the application of Trichoderma harzianum decreased pathogen infection while also increasing the biosynthesis of glycolysis/gluconeogenesis and biosynthesis of cofactors pathway, which were related to growth. This study also aims to enhance our understanding of how melon responds to FOM infection and the mechanisms by which Trichoderma harzianum treatment improves melon resistance at the metabolic level.

Continuous planting results in a higher occurrence rate of oriental melon Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (FOM), and treatment with Trichoderma can considerably alleviate the incidence of disease. However, the tripartite interaction mechanisms among T. harzianum–melon–rhizosphere microorganisms remain poorly understood in current research. Pot experiments elucidate the growth-promoting, antagonistic, and rhizosphere-regulating effects of T. harzianum on oriental melon. The experiment consisted of two treatments: (1) water control (CK), and (2) T. harzianum inoculation (MM) with three repetitions per treatment. Illumina high-throughput sequencing was employed to analyze the microbial community and associated metabolic pathways. Additionally, a comprehensive correlation analysis clarified how T. harzianum-modulated physiological factors regulate soil microbial communities to enhance melon resistance to FOM. T. harzianum inoculation significantly promoted plant growth, decreased the incidence rate of Fusarium wilt by 41.85%, and increased rhizosphere nitrate-N, pH, EC, and soil enzyme activity (e.g., sucrose and alkaline phosphatase). Notably, T. harzianum inoculation altered the rhizosphere microbial community’s relative abundance and structure, with the most striking changes in the fungal community. Principal coordinate analysis showed this fungal restructuring accounted for 44.9% of total community variation (37% from PCo1, 7.9% from PCo2). Soil-borne pathogens (e.g., Fusarium, Verticillium, Phytophthora) decreased in relative abundance with the inoculation of T. harzianum. Meanwhile, the microbial community shifted from a “fungal-dominated” to “bacterial-dominated” state: fungal proportion decreased by 9.47% (from 23.95% in CK to 14.48% in MM), while bacterial proportion increased by 9.47% (from 76.05% in CK to 85.52% in MM). Microbial abundance shifts primarily impacted amino acid and cofactor biosynthesis metabolic pathways. The application of T. harzianum modified the soil environment, restructuring microbial communities through these changes, which in turn regulated microbial metabolic pathways, creating a soil environment conducive to melon growth and thereby enhancing oriental melon resistance to FOM, while mitigating the obstacles of continuous cropping.