Biocontrol Mechanisms of Three Plant Essential Oils Against Phytophthora infestans Causing Potato Late Blight.

Late blight, caused by the notorious pathogen Phytophthora infestans, poses a significant threat to potato (Solanum tuberosum) crops worldwide, impacting their quality as well as yield. Here, we aimed to investigate the potential use of cinnamaldehyde, carvacrol, and eugenol as control agents against P. infestans and to elucidate their underlying mechanisms of action. To determine the pathogen-inhibiting concentrations of these three plant essential oils (PEOs), a comprehensive evaluation of their effects using gradient dilution, mycelial growth rate, and spore germination methods was carried out. Cinnamaldehyde, carvacrol, and eugenol were capable of significantly inhibiting P. infestans by hindering its mycelial radial growth, zoospore release, and sporangium germination; the median effective inhibitory concentration of the three PEOs was 23.87, 8.66, and 89.65 µl/liter, respectively. Scanning electron microscopy revealed that PEOs caused the irreversible deformation of P. infestans, resulting in hyphal shrinkage, distortion, and breakage. Moreover, propidium iodide staining and extracellular conductivity measurements demonstrated that all three PEOs significantly impaired the integrity and permeability of the pathogen's cell membrane in a time- and dose-dependent manner. In vivo experiments confirmed the dose-dependent efficacy of PEOs in reducing the lesion diameter of potato late blight. Altogether, these findings provide valuable insight into the antifungal mechanisms of PEOs vis-à-vis late blight-causing P. infestans. By utilizing the inherent capabilities of these natural compounds, we could effectively limit the harmful impacts of late blight on potato crops, thereby enhancing agricultural practices and ensuring the resilience of global potato food production.

Melatonin extends shelf life in postharvest okra via delaying fruit softening and reducing weight loss.

BACKGROUND: Melatonin, a hormone present in animals and some plants, has garnered attention for its potential in preserving harvested produce. Softening due to changes in cell wall composition and wilting caused by weight loss are the major reasons for the loss of commercial value in postharvest okra. This study aimed to evaluate the impact of melatonin on the softening and weight loss of postharvest okra. RESULTS: The results revealed that the application of melatonin had a significant influence on the maintenance of fruit firmness by inhibiting the breakdown and dissolution of cell wall polysaccharides by suppressing the expression of specific genes responsible for cell wall degradation in okra. Conversely, melatonin treatment positively influenced the expression of genes involved in the synthesis of cell wall components. Furthermore, the treatment exhibited notable benefits in reducing weight loss in okra, which was accomplished by promoting the closure of stomata - the tiny pores on the surface of the fruit. CONCLUSION: Melatonin could serve as a novel approach to reduce water loss, delay fruit softening and extend the shelf life of okra. © 2024 Society of Chemical Industry.

Characterizing the Pathogenicity and Mycotoxin Production Capacity of Fusarium spp. Causing Root Rot of Angelica sinensis in China.

Root rot is a very destructive soil-borne disease, which severely affects the quality and yield of Angelica sinensis in major planting areas of Gansu Province, China. Twelve Fusarium strains were identified from root rot tissue and infected soil in the field by comparing each isolate strain internal transcribed spacer, translation elongation factor 1-α sequence and RNA polymerase second largest subunit gene with the sequences of known fungal species in the NCBI database. Of these isolates, four were F. acuminatum, followed by three F. solani, two F. oxysporum, and one each of F. equiseti, F. redolens, and F. avenaceum. Under greenhouse conditions, pathogenicity testing experiment was carried out using five strains: two F. acuminatum, one F. solani, one F. oxysporum, and one F. equiseti. Among them, the incidence of F. acuminatum-induced root rot on A. sinensis was 100%; hence, it was the most aggressive. Liquid chromatography was used to show that F. acuminatum could produce neosolaniol (NEO), deoxynivalenol, and T-2 toxins. Of these, the level of NEO produced by F. acuminatum was high compared with the other two toxins. By isolating Fusarium spp. and characterizing their toxin-producing capacity, this work provides new information for effectively preventing and controlling A. sinensis root rot in the field as well as improving the quality of its medicinal materials.

Antifungal activity and mechanism of palmarosa essential oil against pathogen Botrytis cinerea in the postharvest onions.

AIMS: Botrytis cinerea is a pathogenic fungus that infests multiple crops, which causes a severe decrease in yield and generates substantial losses in the economy. Palmarosa essential oil (PEO) is a primary aromatic compound extracted from palmarosa that is commonly used for scent, medicine, and flavoring foods due to its diverse bioactive properties. In this study, we explored the antifungal activity and the main mechanism of action of PEO against B. cinerea. In addition, the components and control effects of PEO were also studied. METHODS AND RESULTS: The antifungal assay was tested using the mycelial growth rate method and colony morphology. The constituents of PEO were identified according to gas chromatography/mass spectrometry (GC-MS). The main mechanism of action of PEO was evaluated by measuring representative indicators, which consist of cell contents leakage, excess reactive oxygen species (ROS), and other related indicators. The results indicated that at a concentration of 0.60 ml l-1, PEO exhibits strong antifungal activity against B. cinerea. The PEO mainly included 13 compounds, of which citronellol (44.67%), benzyl benzoate (14.66%), and acetyl cedrene (9.63%) might be the main antifungal ingredients. The study elucidated the main mechanism of action of PEO against B. cinerea, which involved the disruption of cell membrane structure, resulting in altered the cell membrane permeability, leakage of cell contents, and accumulation of excess ROS. CONCLUSIONS: PEO is a satisfactory biological control agent that inhibits B. cinerea in postharvest onions. PEO (0.60 ml l-1) exhibited strong antifungal activity by disrupting the cell membrane structure, altering cell membrane permeability, leading to the cell contents leakage, accumulation of excess ROS and increased level of Malondialdehyde (MDA) compared to the control group.

First Report of Powdery Mildew Caused by Erysiphe cruciferarum on Centella asiatica in China.

Centella asiatica belongs to the Umbelliferae family of perennial herbaceous plants, which are grown worldwide for use as health supplements, edible vegetables and traditional herbs, and are of vital medicinal and edible value in China. (Biswas et al. 2021). In October 2022, the investigation in the 800 m2 garden of Lanzhou (36°06' N,103°43' E) found that more than 80% of C. asiatica plants were infected by powdery mildew, and the leaf infection rate was 90%. The disease severely affects the actual value of C. asiatica. At the beginning of the disease, thin, radial, irregular white colonies appear on the leaves and gradually spread to the stems. The white colony then expands and thickens, covering the upper surface of the whole leaf, and gradually spreading to the lower parts of the stem and leaf. In severe cases, the leaves wither and die. A small portion of fungal spores was glued from the leaf surface with adhesive tape and placed in sterile water for microscopic examination (Zhang et al. 2022). The conidiophore is upright, cylindrical, composed of 3-4 cells, and its size is 72 to 110 × 8 to 10 µm. Conidial pedicels have 16 to 26 µm long cylindrical podocytes. Monoconidia are cylindrical or oval in shape, 16 to 37 µm long, width 11 to 18 µm (n=80). Conidia lack an obvious cellulose body. The bud tube is formed from the end of conidia, and papillary appressorium develops on the epiphytic mycelia. Based on these morphological characteristics, the pathogen was initially identified as Erysiphe cruciferarum (Braun et al. 2012). To validate the identity, the internal transcribed spacer (ITS) of the pathogen (JXC) rDNA was amplified by PCR and sequenced with PM6/ITS5 and PM5/ITS4 primers (Takamatsu et al. 2001). The resulting sequences were registered to GenBank (GenBank Accession OP935627 and OQ253404). At the same time, the ITS sequence size was 535 bp and 521 bp respectively. The ITS sequence of the JXC was 99% (527/534) identical to E.cruciferarum (KT588635) on Eschscholzia californica in Slovakia and 99% (527/534) identical to E.cruciferarum (KC878683) on Chinese Cabbage in China. The ITS sequences from GenBank were subjected to conduct maximum likelihood phylogenetic analysis by MEGA 7.0. The data indicate that strain JXC and E. cruciferarum are clustered on the same branch. The pathogenicity test was performed according to Koch's postulate. By gently pressing the infected leaves on five healthy potted C. asiatica. Meanwhile, five uninoculated plants were used as controls (Zhang et al. 2022). The plants were put into a greenhouse culture (25℃, 14 h light, 10 h dark, humidity ≥ 70%). After 12 days, the inoculated plants showed symptoms of powdery mildew, while the control group had no symptoms. The fungus on the inoculated plant was re-isolated, and identified as E. cruciferarum based on morphological observations and molecular identification. The powdery mildew caused by E.cruciferarum has been reported on Indian mustard in Korea and Chinese cabbage in China, respectively (Kim et al. 2009; Zhao et al. 2014). To our knowledge, this is the first report of C. asiatica powdery mildew caused by E.cruciferarum in China. This finding poses a potential threat to the quality and yield of C. asiatica plants, while providing a preventive basis for the cultivation of C. asiatica.

Analysis of the Small Auxin-Up RNA (SAUR) Genes Regulating Root Growth Angle (RGA) in Apple.

Small auxin upregulated RNAs (SAURs) are primary auxin response genes; the function of regulating root growth angle (RGA) is unclear in the apple rootstock. We firstly identified 96 MdSAUR genes families from new apple genome GDDH13 using the resequence database of 'Baleng Crab (BC)' and 'M9'. A total of 25 MdSAUR genes, regulating the formation of RGA, were screened for the expression profiles in stems and roots and the allelic variants of quantitative trait loci (QTL). Finally, through the joint analysis of network and protein-protein interaction, MdSAUR2, MdSAUR29, MdSAUR60, MdSAUR62, MdSAUR69, MdSAUR71, and MdSAUR84 were screened as the main candidate genes for regulating RGA. This study provides a new insight for further revealing the regulatory mechanism of RGA in apple dwarf rootstocks.

MdWOX4-2 modulated MdLBD41 functioning in adventitious shoot of apple (Malus domestica).

Apple (Malus domestica Borkh.) is not only an important fruit crop distributed worldwide, but also a common model plant. However, the lack of efficient genetic transformation procedures for apples limits the in-depth studies of their gene functions. Although leaf-regenerated adventitious shoots (LRAS) are a prerequisite for successful genetic transformation of apple, little is known about the underlying molecular mechanism of LRAS. Here, we identified the WUSCHEL-related homeobox (WOX) transcription factor in apple, MdWOX4-2, which was a transcriptional activator. Gene expression as well as morphological and histological observations revealed that MdWOX4-2 is involved in the development of LRAS. Overexpression of MdWOX4-2 conferred higher regenerative capacity in transgenic tobacco (Nicotiana tabacum) as compared to the wild type (WT). The combined results of the yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), dual luciferase assays, and transient transactivation assay, revealed that MdWOX4-2 directly bound to and activated the MdLBD41 promoter. Moreover, transgenic experiments further demonstrated that MdLBD41 could significantly enhance the formation of adventitious shoot in transgenic tobacco. Collectively, our findings demonstrate that MdWOX4-2 is important for regulating the LRAS development by activating MdLBD41.

Influence of iron plaque on the uptake and accumulation of chromium by rice (Oryza sativa L.) seedlings: Insights from hydroponic and soil cultivation.

The effects of iron plaque formation on chromium (Cr) uptake and accumulation by rice seedlings (Oryza sativa L.) were assessed using hydroponic and soil experiments, where each 3 levels of Fe supplementation were added to Hoagland solution (0, 30, and 100 mg Fe2+ L-1) and a typical paddy soil (0, 1, and 2 g Fe2+ kg-1). For each treatment, rice seedlings were exposed to different levels of Cr as chromate at 0, 0.5, 2, 5, 10, and 20 mg L-1 in solution or 300 mg kg-1 in soil. Low levels of Cr supply (0.5, 2, and 5 mg L-1) promoted root biomass, while high levels (10 and 20 mg L-1) decreased root and shoot biomass and undermined the density and integrity of iron plaque. Iron supply significantly increased the proportion of Cr in iron plaque, but decreased that in rice plants. The results of hydroponic experiment showed that iron plaque formed with Fe supply at 100 mg L-1 markedly reduced Cr accumulation in shoots of rice seedlings when exposure to 10 and 20 mg L-1 Cr. The soil culture experiment also demonstrated that exogenous Fe addition significantly decreased Cr concentration in leaf and stem of rice seedlings. These results suggested that iron plaque with appropriate amount was effective to reduce the uptake and accumulation of Cr in rice plants, which have strong implication for taking measures to regulate Cr accumulation in rice grains.