Continuous watermelon cropping leads to increases in soil-borne diseases, which negatively affect plant growth. We investigated the impact of continuous watermelon cropping on soil biochemical properties, enzyme activities, microbial biomass, occurrence of Fusarium wilt, diversity and structure of bacterial and fungal communities, as well as the relationship among these factors with plant growth. The results showed significant decreases in soil pH, OM, AN, AP, and AK contents (p < 0.05), while UA, APA, and DA were reduced, along with declines in MBC and MBN in the rhizosphere soil of continuous watermelon cropping (p < 0.05). The population of FON and Fusarium wilt incidence increased significantly after continuous cropping (p < 0.05). High-throughput sequencing analysis revealed that the richness and diversity of soil bacterial and fungal communities significantly decreased (p < 0.05). There were significant differences in bacterial and fungal community composition between the continuous cropping and control groups. Besides, the Pearson correlation analysis of plant growth and environmental factors revealed that soil parameters, including pH, SOM, AN, AP, UA, APA, DA, MBC, and the richness and diversity of bacterial and fungal communities all had significant effects on plant growth. Additionally, the incidence of Fusarium wilt and the population of FON negatively affected growth. In conclusion, we hypothesize that soil acidification, deterioration of biochemical properties, an increase in Fusarium wilt, and changes in microbial community structure are causes of poor watermelon growth.

Natural resistance-associated macrophage proteins (NRAMPs) are able to transport various metal ions across cell membranes, which play an important role in plant growth and development. Here, a survey of cucumber (Cucumis sativus L.) and watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] genomes found a total of five CsNRAMPs and four ClNRAMPs, respectively. Based on the phylogenetic relationships, CsNRAMPs and ClNRAMPs were clustered into three groups (I, II, and III). Five orthologous pairs were identified between cucumber and watermelon genome, and they were clustered on the same branch of the phylogenetic tree. The number of introns in CsNRAMPs and ClNRAMPs ranged from 3 to 13 and the genes from group I were more fragmented than those in group II. Subsequently, analysis of promoter sequences found that five putative transcription factors could act on NRAMPs. Moreover, CsNRAMPs and ClNRAMPs were differentially regulated by deficiencies of iron (Fe), manganese (Mn), copper (Cu), or zinc (Zn), along with toxicities of Fe, Mn, Cu, Zn, or cadmium (Cd). Functional analysis by heterologous expression in yeast indicated that CsNRAMP4 and ClNRAMP3 participate in Cd transport. Overall, the comprehensive analysis of CsNRAMPs and ClNRAMPs reported herein may pave the way for further investigations examining the regulation and functions of this gene family in cucumber and watermelon.

Soil flooding is a well-documented agricultural practice for disease control, but the underlying mechanisms are still poorly understood. The objective of t

Waterlogging-induced hypoxic stress severely impairs vegetative growth and crop yield of melon (Cucumis melo L.). The formation of adventitious roots represents a critical morphological adaptive strategy for melon seedlings to alleviate hypoxic damage and maintain viability under waterlogging conditions. Nevertheless, the synergistic molecular regulatory mechanisms governing waterlogging-triggered adventitious root development in melon remain largely uncharacterized at the proteomic and metabolomic layers. In this study, the waterlogging-tolerant melon line ‘L8’ with superior adventitious root production capacity was exposed to waterlogging treatment, and hypocotyl tissues were harvested at 0, 24, 48 and 72 h post-waterlogging for untargeted metabolomic and proteomic analyses. A total of 1337 differentially accumulated metabolites (DAMs) and 2898 differentially expressed proteins (DEPs) were identified across the pairwise comparisons. Functional enrichment analyses of DAMs and DEPs indicated that pathways related to linoleic acid metabolism, α-linolenic acid metabolism, phenylpropanoid biosynthesis, biosynthesis of secondary metabolites, and glutathione metabolism were centrally implicated in adventitious rooting induced by waterlogging. At the protein level, pivotal functional proteins associated with anaerobic respiration (pyruvate decarboxylase, alcohol dehydrogenase), ethylene biosynthesis (1-aminocyclopropane-1-carboxylate oxidase), cell wall remodeling and antioxidant defense were significantly up-regulated throughout adventitious root development. In addition, three transcription factors, namely the GRAS family protein MELO3C025904.1, MYB-related protein MELO3C007640.1, and ZF-HD protein MELO3C022921.1, exhibited differential expression across different time points compared to the control. Moreover, metabolomic profiling identified three prominent metabolites with regulatory functions, encompassing the terpenoid acorusnol, the piperidine alkaloid 1,4′-bipiperidine-1′-carboxylic acid, and the flavonoid 4′,7-dihydroxy-2′-methoxy-3′-prenylisoflavan. Omics correlation analysis revealed extensive concordance between metabolomic and proteomic profiles. Nine core DAMs, including N-methylserotonin, Val-Val and glyuranolide, were tightly correlated with hundreds of DEPs and key transcription factors, constructing a complex regulatory network governing waterlogging stress acclimation and adventitious root morphogenesis. This study systematically characterizes the coordinated proteomic and metabolomic reprogramming underlying waterlogging-induced adventitious root formation in melon. These findings deepen our understanding of the molecular mechanism of waterlogging tolerance and provide valuable candidate genes and metabolic targets for genetic improvement of waterlogging resistance in melon.