Fusarium oxysporum f. sp. radicis-lycopersici (Forl) is a destructive soil-borne phytopathogenic fungus that causes Fusarium crown and root rot (FCRR) of tomato, leading to considerable field yield losses. In this study, we explored the antifungal capability of linalool, a natural plant volatile organic component, against Forl and its role in controlling FCRR symptoms in tomatoes. Our results showed that Forl mycelial growth was inhibited by the linalool treatment and that the linalool treatment damaged cell membrane integrity, enhanced reactive oxygen species levels, depleted glutathione, and reduced the activities of many antioxidant enzymes in Forl. Transcriptomic and proteomic analyses demonstrated that linalool also downregulated metabolic biosynthetic pathways at the transcript and protein levels, including redox, transporter activity, and carbohydrate metabolism in Forl. Moreover, linalool significantly decreased the expression of many Forl pathogenic genes, such as cell wall degrading enzymes (CWDEs) and G proteins, which is likely how a Forl infection was prevented. Importantly, exogenously applied linalool activated the salicylic acid (SA) and jasmonic acid (JA) defensive pathways to improve disease resistance and relieved the negative effects of Forl on plant growth. Taken together, we report that linalool is an effective fungicide against Forl and will be a promising green chemical agent for controlling FCRR.

Gray mold is a disease that often occurs in postharvest tomato fruits, leading to a significant decline in the fruits’ quality. In production, pesticides are mostly used to control gray mold, which negatively affect both the environment and food safety. The purpose of this article is to study the effects of linalool fumigation on controlling gray mold in tomato fruits and to further investigate the mechanism of linalool function, so as to provide technical support and a theoretical basis for the application of linalool in the green control of tomato gray mold. The results of the in vitro experiments showed that linalool fumigation had a strong inhibitory effect on the mycelial growth of Botrytis cinerea and that the fumigation of linalool inhibited the expansion of pathogens on tomato fruits. The disease index of tomato fruits in the linalool treatment was always lower than that of the control within 72 h after inoculation with Botrytis cinerea; at the end of experiment, the disease index of the control reached 100.0, which was only 8.0 with the 30 μL/L linalool treatment. Linalool fumigation increased the antioxidant capacity of the tomato fruits under Botrytis cinerea infection through regulating activities of SOD, POD and CAT as well as the ascorbic acid (AsA) content, which could be responsible for the lower malondialdehyde (MDA) accumulation. Linalool fumigation increased the activities of polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) in tomato fruits, indicating that secondary metabolism was involved in the function of linalool in the regulation of tomato fruit resistance to pathogens. As the main enzymes related to cell structure, polygalacturonase (PG), cellulase (CL) and β-galactosidase (β-GAL) were inhibited by linalool, which could protect cell wall structures from damage, and strengthened the mechanical barrier against pathogen access to fruit flesh.

The Lateral Organ Boundaries Domain (LBD) gene family encodes plant-specific transcription factors that play pivotal roles in growth, development, and stress responses. However, a comprehensive genome-wide analysis of the LBD family in watermelon (Citrullus lanatus) has not been conducted until now. In this study, we identified 39 ClLBD genes using the latest watermelon reference genome and systematically analyzed the function of ClLBD2 in root development. These ClLBDs are unevenly distributed across 10 chromosomes except Chr4. Evolutionary analysis grouped the gene family members into six subgroups: Class I (a–e) and Class II. Physicochemical properties and gene structure analysis showed that the ClLBD protein members are tightly conserved. In the promoter regions of ClLBD genes, we identified abundant cis-acting regulatory elements related to abiotic stress and hormone responses. Through RNA-seq analysis from a cucurbit database, we found that several ClLBD genes showed high relative expression in roots, with ClLBD2 being the most highly expressed. Since its subfamily includes AtLBD25, a known root development-related gene, we hypothesized that ClLBD2 might be involved in root development. To validate this, ClLBD2-edited roots were generated using the CRISPR-Cas9 system and Agrobacterium rhizogenes-mediated transformation. Compared to the wild type, the ClLBD2 edited roots exhibited significant reduction in taproot length and lateral root numbers, indicating that ClLBD2 may regulate root development. This study provides the first comprehensive analysis of the LBD gene family in watermelon, offering valuable insights for evolutionary and further functional studies of ClLBD genes.