Background and aimsContinuous cropping obstacles (CCOs) are frequently encountered during the cultivation of Lagenaria siceraria (L. siceraria) in the same field for many years, which is related to the secondary metabolites secreted by plants, among which vanillin is one of the factors causing CCOs of L. siceraria. This study investigated the effects of different concentrations of exogenous brassinolide (BR) on L. siceraria under CCOs.MethodsHigh-performance liquid chromatography (HPLC) was used to determine the contents of vanillin in rhizosphere soil of non-planted soil, 1-year-old, 2-year-old, and 3-year-old L. siceraria cultivation. This study investigated the effects of BR at concentrations of 0.05, 0.10, 0.20 and 0.40 mg/mL on L. siceraria under CCOs by applying 6.00 mg/mL vanillin to simulate CCOs.ResultsThe contents of vanillin in the rhizosphere soil of non-planted soil, 1-year-old, 2-year-old, and 3-year-old were 0.01, 0.03, 0.06 and 0.10 mg/g. The BR could effectively alleviate the stress imposed by vanillin and enhance the tolerance of L. siceraria to vanillin stress. When the concentration of BR was 0.20 mg/mL, the alleviation effect on vanillin stress was the most significant. Compared with the vanillin stress group, the plant height, the projected area of the root, number of tips, and total root length enhanced by 1.52, 4.21, 4.43, and 6.12 times. When the light intensity was 1200 lx, the transpiration rate and stomatal conductance increased by 68.57% and 48.00%. At the same time, the antioxidant enzyme activities had the best alleviation at 0.20 mg/mL.ConclusionThe vanillin significantly inhibited the growth of L. siceraria seedlings at elevated concentrations. Furthermore, its persistent accumulation in the soil via root exudation was identified as a contributing factor to CCOs. It was worth noting that 0.20 mg/mL BR could alleviate the damage caused by CCOs to L. siceraria seedlings.

Crops produced using the practice of continuous cropping can become seriously damaged by plant-parasitic nematodes, an important indicator of continuous cropping obstacles. As a typical and important perennial economic crop, dragon fruit is prone to serious plant-parasitic nematode infestation; however, whether it encounters continuous cropping obstacles remains unclear. Here, we studied plant-parasitic nematodes (Meloidogyne spp. and Tylenchorhynchus sp.) in the soil and roots, soil nematode communities, metabolic footprint, soil integrated fertility, and the yield of intensively planted dragon fruit under non-continuous cropping (Y1) and 3 years (Y3) and 5 years (Y5) of continuous cropping, to determine potential continuous-cropping obstacles and factors that affect the yield of this fruit. The largest numbers of plant-parasitic nematodes in the soil and roots were observed in Y5; the associated yield was reduced, and the dragon fruit was severely stressed. Further analysis of the composition, diversity, and ecological function indices of soil nematodes showed that the soil ecological environment deteriorated after 3 years of continuous cropping, with Y5 having the worst results. Similarly, the soil at Y5 had a significant inhibitory effect on the growth and reproduction of Caenorhabditis elegans. Mantel test analysis and a random forest model showed that soil available phosphorus, soil exchange calcium, and soil nematode abundance and diversity were related significantly to yield. Partial least squares path modeling revealed that soil fertility and soil nematode diversity directly impacts the yield of continuously cropped dragon fruit. In summary, continuous cropping obstacles occurred in Y5 of intensive dragon fruit cultivation, with soil nematode diversity and soil fertility determining the crop's yield.

Understanding the mechanisms that give rise to obstacles in the continuous cultivation of C. pilosula is essential for addressing or mitigating these challenges. The findings of this study suggest that repeated cultivation significantly reduced the content of polysaccharide in roots, and significantly increased the dead seedling rate in the field. The vascular bundles of the affected plant were extensively colonized by fungi. Furthermore, the root vascular bundles exhibit significant woodiness and corkiness, accompanied by cellular fractures and structural collapse. It was determined that the pathogenic endophyte is Fusarium oxysporum, and the exacerbated disease manifestation corresponds to an acute wilting type. Additionally, the root-zone soil microorganisms Cladosporium austroafricanum, Fusarium foetens, Fusarium petersiae, and Acaulium retardatum may significantly contribute to the yield-reducing phenomenon associated with continuous cropping. The proliferation of pathogenic bacteria during continuous cultivation initiates a complex interaction mechanism between the host plant and these pathogens. This process is characterized by a rapid increase in calcium ion (Ca2+) concentration, which subsequently leads to an upsurge in reactive oxygen species (ROS), particularly manifested as elevated levels of hydrogen peroxide (H2O2). Additionally, this response triggers thickening of cell walls and other immune mechanisms aimed at inhibiting the invasion of pathogenic bacteria. At the same time, to prevent ROS from inducing oxidative damage and triggering oxidative stress, there is a notable increase in both antioxidant enzyme activity and antioxidant substances content.

Calcium-dependent protein kinase (CDPK) is an important mediator for Ca2 + signal recognition and transduction, playing a crucial role in plant stress response. Previous studies have shown that PcCDPK5 may be involved in the response of patchouli to p-hydroxybenzoic acid (p-HBA) stress. In this study, we further found that the subcellular localization of PcCDPK5 protein is in the cytoplasm, and its gene expression is closely related to continuous cropping (CC) and p-HBA stress. Under p-HBA stress, silencing the PcCDPK5 homologous gene in Nicotiana tabacum leads to decreased antioxidant enzyme activity and increased malondialdehyde (MDA) content, significantly accumulating reactive oxygen species (ROS) and affecting normal plant growth. On the contrary, overexpression of PcCDPK5 can effectively alleviate the damage caused by p-HBA stress to plant bodies. Through this research, the function of PcCDPK5 in response to p-HBA stress has been preliminarily analyzed, laying a theoretical foundation for alleviating CC obstacles in patchouli.

Root-knot nematodes (Meloidogyne spp.) have garnered significant attention from researchers owing to the substantial damage they cause to crops and their worldwide distribution. However, controlling these nematodes is challenging because a limited number of chemical pesticides and biocontrol agents are effective against them. Here, we demonstrate that pepper rotation markedly reduces Meloidogyne incognita infection in cucumber and diminishes the presence of p-hydroxybenzoic acid in the soil, a compound known to exacerbate M. incognita infection. Pepper rotation also restructures the rhizobacterial community, leading to the colonization of the cucumber rhizosphere by two Pseudarthrobacter oxydans strains (RH60 and RH97), facilitated by enrichment of palmitic acid in pepper root exudates. Both strains exhibit high nematocidal activity against M. incognita and have the ability to biosynthesize indoleacetic acid and biodegrade p-hydroxybenzoic acid. RH60 and RH97 also induce systemic resistance in cucumber plants and promote their growth. These data suggest that the pepper root exudate palmitic acid alleviates M. incognita infection by recruiting beneficial P. oxydans to the cucumber rhizosphere. Our analyses identify a novel chemical component in root exudates and reveal its pivotal role in crop rotation for disease control, providing intriguing insights into the keystone function of root exudates in plant protection against root-knot nematode infection.

The additions of microbial organic fertilizer (MOF), a microbial inoculant (MI), and quicklime (Q) are considered to be sustainable practices to restore land that has been damaged by continuous cropping of pepper (Capsicum annuum L.). However, the combined effects of these three additives on pepper yield, soil chemical properties, and soil microbial communities were unclear. The experimental design consists of 13 treatment groups: the untreated soil (control); soil amended solely with three treatments for each of MOF (1875-5625 kg ha-1), MI (150-450 mL plant-1), and Q (1500-4500 kg ha-1); and soil amended with combinations of MOF, MI, and Q at three comparable concentrations. A significant increase in pepper fruit diameter, length, yield, and soil available nitrogen, phosphorus, and potassium contents occurs upon exclusive and combined applications of MOF, MI, and Q. Pepper yield was greatest (29.89% more than control values) in the combined treatment with concentrations of 1875 kg ha-1 MOF, 150 mL plant-1 MI, and 1500 kg ha-1 Q. The application of Q increased soil pH and reduced soil-fungal richness. The application of MOF, MI, and Q increased the relative abundance of bacterial genera and the complexity of bacterial and fungal co-occurrence networks compared with control levels. The combined application of MOF, MI, and Q resulted in the greatest microbial network complexity. A Mantel test revealed the key role of soil available nitrogen content and bacterial diversity in the regulation of pepper growth and yield. We conclude that the combined application of MOF, MI, and Q improves soil nutrient availability and modifies soil microbial community composition, significantly promoting plant growth and pepper yield during continuous cultivation.

PurposeThe health of rhizosphere soil microorganisms is an important indicator to evaluate soil quality. Therefore, understanding the response of rhizosphere soil microorganisms to tobacco crop succession is crucial for promoting the sustainable development of agriculture.MethodsThe microbial diversity and community structure of rhizosphere soil in continuous cropping and non-cropped tobacco for 7 years were analyzed by the Illumina platform.Result(1) Continuous cropping tobacco cause rhizosphere soil acidification and reduction in alkaline nitrogen (AN) and soil organic matter (SOM). (2) Continuous cropping tobacco reduces the diversity of rhizosphere soil microbial communities, increasing harmful functional microorganisms and declining beneficial ones. (3) The abundance of bacteria that perform nitrification and saprophytic fungi in the rhizosphere soil of continuous cropping areas decreases, inhibiting carbon and nitrogen cycling processes. (4) The composition and diversity of the soil rhizosphere microbial community are affected by the imbalance in the physicochemical property of the rhizosphere.ConclusionContinuous cropping tobacco cause rhizosphere soil acidification and nutrient imbalance, and the carbon and nitrogen cycles involved in microorganisms were damaged. Furthermore, the decreased diversity of rhizosphere soil microorganisms and the increased abundance of pathogenic fungi contribute to the continuous cropping obstacles of tobacco.