Role of grafting in vegetable crops grown under saline conditions

Salinity isoneofthemajorabioticstressesthatreduceplantgrowthandcropproductivityinmanyveg- etable productionareasoftheworld.Graftingcanrepresentaninterestingtooltoavoidorreduceyield losses causedbysalinitystressinhigh-yieldinggenotypesbelongingto Solanaceae and Cucurbitaceae families. Graftingisanintegrativereciprocalprocessand,therefore,bothscionandrootstockcaninflu- ence salttoleranceofgraftedplants.Graftedplantsgrownundersalineconditionsoftenexhibitedbetter growth andyield,higherphotosynthesisandleafwatercontent,greaterroot-to-shootratio,higheraccu- mulation ofcompatibleosmolytes,abscisicacidandpolyaminesinleaves,greaterantioxidantcapacity in leaves,andloweraccumulationofNa+ and/or Cl− in shootsthanungraftedorself-graftedplants. This reportgivesanoverviewoftherecentliteratureonthesalinityresponseofgraftedplantsandthe mechanisms ofsalttoleranceingraftedplantsrelatedtothemorphologicalrootcharacteristicsandthe physiological andbiochemicalprocesses.Thereviewwillconcludebyidentifyingseveralprospectsfor future researchesaimingtoimprovetheroleofgraftinginvegetablecropsgrownundersalineconditions

Spatial–Temporal Response of Reactive Oxygen Species and Salicylic Acid Suggest Their Interaction in Pumpkin Rootstock-Induced Chilling Tolerance in Watermelon Plants

Grafting with pumpkin rootstock could improve chilling tolerance in watermelon, and salicylic acid (SA) as a signal molecule is involved in regulating plant tolerance to chilling and other abiotic stresses. To clarify the mechanism in pumpkin rootstock-induced systemic acquired acclimation in grafted watermelon under chilling stress, we used self-grafted (Cl/Cl) and pumpkin rootstock-grafted (Cl/Cm) watermelon seedlings to study the changes in lipid peroxidation, photosystem II (PSII) activity and antioxidant metabolism, the spatio–temporal response of SA biosynthesis and H2O2 accumulation to chilling, and the role of H2O2 signal in SA-induced chilling tolerance in grafted watermelon. The results showed that pumpkin rootstock grafting promoted SA biosynthesis in the watermelon scions. Chilling induced hydrolysis of conjugated SA into free SA in the roots and accumulation of free SA in the leaves in Cl/Cm plants. Further, pumpkin rootstock grafting induced early response of antioxidant enzyme system in the roots and increased activities of ascorbate peroxidase and glutathione reductase in the leaves, thus maintaining cellular redox homeostasis. Exogenous SA improved while the inhibition of SA biosynthesis reduced chilling tolerance in Cl/Cl seedlings. The application of diphenyleneiodonium (DPI, inhibitor of NADPH oxidase) and dimethylthiourea (DMTU, H2O2 scavenger) decreased, while exogenous H2O2 improved the PSII activity in Cl/Cl plants under chilling stress. Additionally, the decrease of the net photosynthetic rate in DMTU- and DPI-pretreated Cl/Cl plants under chilling conditions could be alleviated by subsequent application of H2O2 but not SA. In conclusion, pumpkin rootstock grafting induces SA biosynthesis and redistribution in the leaves and roots and participates in the regulation of antioxidant metabolism probably through interaction with the H2O2 signal, thus improving chilling tolerance in watermelon

MIX-NET: Deep Learning-Based Point Cloud Processing Method for Segmentation and Occlusion Leaf Restoration of Seedlings

In this paper, a novel point cloud segmentation and completion framework is proposed to achieve high-quality leaf area measurement of melon seedlings. In particular, the input of our algorithm is the point cloud data collected by an Azure Kinect camera from the top view of the seedlings, and our method can enhance measurement accuracy from two aspects based on the acquired data. On the one hand, we propose a neighborhood space-constrained method to effectively filter out the hover points and outlier noise of the point cloud, which can enhance the quality of the point cloud data significantly. On the other hand, by leveraging the purely linear mixer mechanism, a new network named MIX-Net is developed to achieve segmentation and completion of the point cloud simultaneously. Different from previous methods that separate these two tasks, the proposed network can better balance these two tasks in a more definite and effective way, leading to satisfactory performance on these two tasks. The experimental results prove that our methods can outperform other competitors and provide more accurate measurement results. Specifically, for the seedling segmentation task, our method can obtain a 3.1% and 1.7% performance gain compared with PointNet++ and DGCNN, respectively. Meanwhile, the R2 of leaf area measurement improved from 0.87 to 0.93 and MSE decreased from 2.64 to 2.26 after leaf shading completion

Design and Experiment of Full-Tray Grafting Device for Grafted Melon Seedling Production

At present, the existing vegetable grafting machines are cutting and grafting operations for a single plant or row. They need to manually or automatically grab the seedlings, and their grafting efficiency is not significantly higher than that of manual grafting techniques. In this paper, grafted melon seedlings were the subject of the research. Based on the splice-grafting method, we designed a clamping and positioning device for full-tray seedlings and a mechanical device to realize full-tray grafting by locating the vegetable seedlings and completing the full-tray grafting process without damaging the seedlings. The results show that the cutting success rate for pumpkin rootstock and for melon scion reached 100% and 92%, respectively. The lengths of the long axis of the section of the rootstock and the scion were 6.2–7.7 mm, and the cutting angle was maintained at 30 degrees, thereby able to meet the requirements of the grafting method. The average grafting efficiency for the rootstock and scion were 2134 plants/h, and the average grafting success rate was 67%

Priming Watermelon Resistance by Activating Physiological Response and Defense Gene Expression to Alleviate Fusarium Wilt in Wheat-Watermelon Intercropping

Wheat intercropping in watermelon could provide relief from the occurrence of Fusarium wilting of watermelon, a severe soil-borne disease caused by the fungus Fusarium oxysporum f. sp. niveum (FON). The current study aims to investigate the effect of root exudates from three wheat cultivars and one watermelon cultivar on the growth of FON and the responses of Fusarium wilt in watermelon to intercropping with wheat. The results revealed the contrasting effects of root exudates on the mycelial growth of FON; the wheat root exudates inhibited the mycelial growth of FON, and watermelon root exudates promoted the mycelial growth of FON. Watermelon plants suffered less Fusarium wilt in the intercropping system than in the monocropping system. Wheat intercropping reduced the incidence of Fusarium wilt in watermelon, and this effect was associated with the role of wheat root exudates that inhibited the growth of FON. Malondialdehyde (MDA) contents decreased in the intercropping system compared with the monocropping system after FON inoculation. The catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and polyphenol oxidase (PPO) activities, and total phenolics and flavonoid contents in the roots of watermelon in the intercropping system were significantly higher than those in the monocropping system. Real-time PCR analysis showed that ClCAT, ClSOD, ClAPX, and ClPPO defensive enzymes and ClPDF2.1 and ClPDF2.4 defensin-like gene expression were significantly induced during the early stage after FON inoculation in the intercropping system compared to the monocropping system, while peroxidases did not show a significant response to FON infection. It is suggested that intercropping with wheat alleviates Fusarium wilt of watermelon by reducing the population of FON in rhizospheric soil and activating physiological responses and defense gene expression to protect watermelon from FON infection and improve the resistance of watermelon to FON in the intercropping system

Early Identification and Localization Algorithm for Weak Seedlings Based on Phenotype Detection and Machine Learning

It is important to propose the correct decision for culling and replenishing seedlings in factory seedling nurseries to improve the quality of seedlings and save resources. To solve the problems of inefficiency and subjectivity of the existing traditional manual culling and replenishment of seeds, this paper proposes an automatic method to discriminate the early growth condition of seedlings. Taking watermelon plug seedlings as an example, Azure Kinect was used to collect data of its top view three times a day, at 9:00, 14:00, and 19:00. The data were collected from the time of germination to the time of main leaf growth, and the seedlings were manually determined to be strong or weak on the last day of collection. Pre-processing, image segmentation, and point cloud processing methods were performed on the collected data to obtain the plant height and leaf area of each seedling. The plant height and leaf area on the sixth day were predicted using an LSTM recurrent neural network for the first three days. The R squared for plant height and leaf area prediction were 0.932 and 0.901, respectively. The dichotomous classification of normal and abnormal seedlings was performed using six machine learning classification methods, such as random forest, SVM, and XGBoost, for day six data. The experimental results proved that random forest had the highest classification accuracy of 84%. Finally, the appropriate culling and replenishment decisions are given based on the classification results. This method can provide some technical support and a theoretical basis for factory seedling nurseries and transplanting robots

Redox Signaling and CBF-Responsive Pathway are Involved in Salicylic Acid-Improved Photosynthesis and Growth under Chilling Stress in Watermelon

Salicylic acid (SA) plays an important role in plant response to abiotic stresses. This study investigated the potential role of SA in alleviating the adverse effects of chilling stress on photosynthesis and growth in watermelon (Citrullus lanatus). Chilling stress induced the simultaneous accumulation of free and conjugated SA in watermelon plants, and the chilling-induced SA production was attributed to the phenylalanine ammonia-lyase pathway. Applying SA at moderate concentrations induced chilling tolerance, whereas inhibition of SA biosynthesis by L-ɑ-aminooxy-β-phenylpropionic acid (AOPP) increased the photooxidation of PS II under chilling stress in watermelon, resulting in reduced photosynthesis and growth. Chilling induced a transient increase in the ratios of reduced to oxidized glutathione and reduced ascorbate to dehydroascorbate. Then, the expression of antioxidant genes was upregulated, and the activities of antioxidant enzymes were enhanced. Furthermore, SA-induced chilling tolerance was associated with cellular glutathione and ascorbate homeostasis, which served as redox signals to regulate antioxidant metabolism under chilling stress. AOPP treatment stimulated the chilling-induced expression of cold-responsive genes, particularly via C-repeat binding factors CBF3 and CBF4. These results confirm the synergistic role of SA signaling and the CBF-dependent responsive pathway during chilling stress in watermelon

Overexpression of Melon Tonoplast Sugar Transporter CmTST1 Improved Root Growth under High Sugar Content

Sugar allocation is based on the source-to-sink and intracellular transport between different organelles, and sugar transporters are usually involved in these processes. Tonoplast sugar transporters (TST) are responsible for transporting sugar into vacuoles; however, the role of TSTs in root growth and the response to abiotic stress is poorly studied. Here, RNA analysis and promoter-β-glucuronidase staining revealed that a melon TST1 gene (CmTST1) is highly expressed in the roots. The sugar feeding experiment results showed that the expression of CmTST1 in the roots was induced by a relatively high level of sucrose (6%), glucose (3%), and fructose (3%). The ectopic overexpression of CmTST1 in Arabidopsis improved the root and shoot growth of seedlings under high exogenous sugar stress. Furthermore, the ectopic expression of CmTST1 promoted the expression of plasma membrane-located sugar transporters. We proposed that CmTST1 plays a key role in importing sugar transport into the vacuoles of roots in response to metabolic demands to maintain cytosolic sugar homeostasis

Assessment of suitable reference genes for quantitative gene expression studies in melon fruits

Melon (Cucumis melo. L) is an attractive model plant for investigating fruit development because of its morphological, physiological, and biochemical diversity. Quantification of gene expression by quantitative reverse transcription PCR (qRT-PCR) with stably expressed reference genes for normalization can effectively elucidate the biological functions of genes regulating fruit development. However, the reference genes for data normalization in melon fruits have not yet been systematically validated. In this study, 20 candidate reference genes were assessed for their potential use as reference genes in melon fruits. GeNorm and NormFinder analyses showed that Cytosolic ribosomal protein S15 (CmRPS15) was the preferred single reference gene. While, CmRPS15 and Ribosomal protein L (CmRPL), or RAN GTPase (CmRAN) and TATA-box binding protein (CmTBP2) were the suitable reference gene combinations in melon fruits. Reliabilities of these identified genes was further validated by the parallel analyses of sucrose contents, activities of soluble acid invertase (AI) and sucrose phosphate synthase (SPS), and expression profiles of their respective encoding genes CmAIN2 and CmSPS1 during melon fruit ripening. These validated reference genes will help to improve the accuracy of gene expression quantification in melon fruits