Aluminum (Al) toxicity severely restricts crop growth and productivity in acidic soils. The rubber tree is one of the most economically important crops in tropical regions, which is tolerant to high concentrations of Al in sand or hydroponic culture conditions compared with other plants that have been reported. However, the mechanisms of Al tolerance in rubber trees remain unknown. In this study, we conducted a transcriptome and metabolome analysis for rubber tree sapling roots treated with 200 mM Al for 0 (CK), 2 or 5 days, respectively. Compared with the CK, a total of 9534 differentially expressed genes (DEGs) and 3821 differentially expressed metabolites (DEMs) were identified in 2 d of Al treatment. There were 10,373 DEGs and 4636 DEMs after 5 d of Al treatment, and 1626 DEGs and 1674 DEMs between 2 and 5 d of Al treatment. The DEGs mainly concentrated in transporters, transcription factors (TFs), cell wall biosynthesis and antioxidant systems, and the DEMs were mainly focused on lipids and lipid-like molecules, organic acids and derivatives, organic oxygen compounds, phenylpropanoids and polyketides. The combined transcriptome and metabolome analysis indicated DEGs and DEMs involved in ABC transporters, glutathione metabolism, flavonoid biosynthesis and phenylalanine metabolic pathways were identified to be closely associated with the Al tolerance of rubber trees. Our study elucidated the mechanism of rubber trees’ tolerance to Al at the transcriptional and metabolic levels, which provides a theoretical basis for the study of Al tolerance both for rubber trees and other woody plants.

Wax gourd wilt is a devastating fungal disease caused by a specialized form of Fusarium oxysporum Schl. f. sp. benincasae (FOB), which severely restricts the development of the wax gourd industry. Resistant rootstock pumpkin grafting is often used to prevent and control wax gourd wilt. The “Haizhan 1” pumpkin has the characteristic of high resistance to wilt, but the mechanism through which grafted pumpkin rootstock plants acquire resistance to wax gourd wilt is still poorly understood. In this study, grafted wax gourd (GW) and self-grafted wax gourd (SW) were cultured at three concentrations [2.8 × 10⁶ Colony Forming Units (CFU)·g⁻¹, 8.0 × 10⁵ CFU·g⁻¹, and 4.0 × 10⁵ CFU·g⁻¹, expressed by H, M, and L]. Three culture times (6 dpi, 10 dpi, and 13 dpi) were used to observe the incidence of wilt disease in the wax gourd and the number of F. oxysporum spores in different parts of the soil and plants. Moreover, the physiological indices of the roots of plants at 5 dpi, 9 dpi, and 12 dpi in soil supplemented with M (8.0 × 10⁵ CFU·g⁻¹) were determined. No wilt symptoms in GW. Wilt symptoms in SW were exacerbated by the amount of FOB in the inoculated soil and culture time. At any culture time, the amount of FOB in the GW soil under the three treatments was greater than that in the roots. However, for the SW treatments, at 10 dpi and 13 dpi, the amount of FOB in the soil was lower than that in the roots. The total phenol (TP) and lignin (LIG) contents and polyphenol oxidase (PPO) and chitinase (CHI) activities were significantly increased in the GW_M roots. The activities of phenylalanine ammonia lyase (PAL) and peroxidase (POD) initially decreased but then increased in the GW_M roots. When the TP content decreased significantly, the LIG content and PAL and CHI activities increased initially but then decreased, whereas the PPO and POD activities did not change significantly in the SW_M roots. The results indicated that the roots of the “Haizhan 1” pumpkin stock plants initiated a self-defense response after being infected with FOB, and the activities of PPO, POD, PAL, and CHI increased, and additional LIG and TP accumulated, which could effectively prevent FOB infection.

Wax gourd wilt (WGW) is a destructive soil-borne disease, and grafting pumpkin rootstocks offers effective and eco-friendly control. “Haizhan 1” pumpkin rootstock exhibits superior disease resistance compared to Cucurbita ficifolia, with root exudates improving soil microecology. However, the specific root exudate components involved in wilt resistance and their effects on soil microbial diversity remain unclear. In this paper, “Haizhan 1” pumpkin, Cucurbita ficifolia pumpkin and “Tiezhu 168” wax gourd are taken as rootstock materials to graft and obtain the five kinds of experimental subjects (H_T, B_T, H_H, B_B, T_T). Root exudates from five grafted combinations were analyzed by using metabolomics. Ten key metabolites that have direct fungicidal effects and indirect regulatory effects on disease resistance were identified, including Melilotoside A, a substance unique to pumpkin-wax gourd grafting. Potted experiments revealed that root exudates from resistant (H_T), moderately resistant (B_T), and susceptible (T_T) plants altered soil microbial communities under Fusarium oxysporum challenge. High-throughput sequencing identified six key bacteria linked to disease resistance: norank_f__norank_o_0319-6G20, Haliangium, norank_f__norank_o__norank_c__OLB14, Thermomonas, Brevundimonas, and Gemmatimonas. Correlation analysis highlighted the interaction between root exudate metabolites and soil microbes. This study clarifies the role of root exudates in WGW resistance and provides a foundation for developing biocontrol strategies.