Nanoparticles and Carrot Health: Impact on Growth, Pigments, Proline, and Disease Resistance -

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Nanoparticles and Carrot Health: Impact on Growth, Pigments, Proline, and Disease Resistance

 

Introduction:  Carrot (Daucus carota L.) is a highly valued root vegetable prized for its nutritional content and flavor. Its popularity stems from its rich source of vitamins, minerals, and fibers, making it a valuable dietary addition. Despite its benefits, carrot cultivation faces numerous challenges, including various plant pathogens that significantly impact yield and quality. Key disease culprits include:

Bacterial soft-rot by Pectobacterium carotovorum

Bacterial leaf blight by Xanthomonas campestris pv. carotae

Root-knot by Meloidogyne spp.

Fungal leaf blight by Alternaria dauci

Rot by Fusarium solani

These pathogens cause various symptoms like tissue maceration, leaf spots, root galls, and rotting, jeopardizing the health and productivity of carrot plants.

Nanotechnology as a Potential Solution: Conventional methods for plant disease management often have limitations or drawbacks. Nanotechnology offers a promising alternative with its potential for green and eco-friendly solutions. Nanoparticles like graphene oxide (GO) and zinc oxide (ZnO) possess unique properties like high surface area, antimicrobial activity, and reduced toxicity, making them attractive candidates for plant disease control. Current research highlights the potential of nanomaterials in managing plant diseases. Graphene with its exceptional properties shows promise, but individual graphene sheets or GO exhibit limited antibacterial activity. ZnO nanoparticles, on the other hand, demonstrate remarkable antimicrobial properties and promote plant growth, making them a valuable tool for agriculture. Notably, ZnO NPs exhibit lower toxicity to plants and beneficial soil bacteria compared to other options. This study aimed to explore the efficacy of GO and ZnO nanoparticles as a management strategy for the aforementioned carrot diseases (Pectobacterium carotovorum, Xanthomonas campestris pv. carotae, Meloidogyne javanica, Alternaria dauci, and Fusarium solani). By focusing on foliar application, the study minimized nanoparticle interaction with the soil ecosystem, potentially reducing environmental risks. Additionally, the study investigated the impact of both nanoparticles on plant growth and physiological responses.

Methodology:

Pathogen Isolations and Identification: Root-knot nematodes (Meloidogyne javanica): Identified from root galls based on perineal patterns and confirmed through soil extraction techniques. Fungi (Alternaria dauci and Fusarium solani): Isolated from infected shoots and roots, identified by colony morphology, growth rate, and conidial characteristics. Bacteria (Pectobacterium carotovorum and Xanthomonas campestris pv. carotae): Isolated from diseased tissues, identified through standard biochemical and physiological tests.

 Nanoparticle Solutions: Graphene oxide (GO) solutions prepared at 0.05 and 0.10 mg/ml concentrations. Zinc oxide (ZnO) nanoparticle solutions prepared at 0.005 and 0.01% concentrations.

Nematode Hatching and Mortality Assay: Egg masses exposed to GO and ZnO solutions of varying concentrations to assess hatching inhibition and mortality rate.

 Antifungal Activity: GO and ZnO solutions incorporated into culture media to evaluate their effect on fungal growth.

Antibacterial Activity: Paper discs containing GO and ZnO solutions placed on agar plates with bacterial cultures to measure inhibition zones.

Plant Growth and Inoculation: Carrot seeds sown in sterilized soil mixture in pots. Plants inoculated with individual pathogens (M. javanica, P. carotovorum, X. campestris pv. carotae, A. dauci, F. solani) or left uninoculated (control). Foliar application of GO and ZnO solutions at different concentrations or water (control) applied after inoculation.

Data Collection and Analysis: Plant growth parameters (length, dry weight) and disease severity indices measured after 90 days. Nematode population in soil and roots quantified. Chlorophyll, carotenoid, and proline content in leaves determined.

Results:-

GO and ZnO NPs Inhibit Bacteria, Fungi, and Nematodes:

Both NPs inhibited bacterial growth, with ZnO being more effective than GO. NPs also reduced the growth of fungi, again with ZnO showing stronger antifungal activity. Nematode hatching and mortality were significantly inhibited by both NPs, with ZnO again being more potent. The inhibitory effects increased with higher NP concentrations.

Greenhouse Experiment Summary:

Plant Growth and Physiology: Fungal infection (F. solani) caused the greatest reduction in plant growth, followed by A. dauci and P. carotovorum. Foliar application of both GO and ZnO NPs significantly increased plant growth, chlorophyll, carotenoid, and proline content compared to controls. ZnO NPs at 0.1 mg/ml were most effective in enhancing growth and physiological parameters.

Disease Resistance: Both NPs significantly reduced symptoms of soft rot, leaf blight, root knot, leaf spot, and root rot caused by various pathogens. ZnO NPs at 0.1 mg/ml offered the best protection against all diseases.

Effects on Galling and Disease Indices: Both GO and ZnO NPs reduced galling and nematode population of M. javanica. ZnO at 0.1 mg/ml was most effective, followed by ZnO at 0.05 mg/ml, GO at 0.1 mg/ml, and GO at 0.05 mg/ml. Disease indices for various pathogens were initially 4. Spraying with GO or ZnO NPs (both concentrations) reduced the indices to 2. ZnO at 0.1 mg/ml achieved the best disease control, reducing indices to 1.

Conclusion:-

This study demonstrated that both graphene oxide (GO) and zinc oxide (ZnO) nanoparticles (NPs) effectively enhanced the growth and health of carrot plants. Application of both NPs, particularly ZnO at a concentration of 0.10 mg/ml, significantly increased plant growth, chlorophyll, carotenoid, and proline content compared to infected or uninfected controls. Furthermore, both NPs reduced the severity of various diseases and nematode infestations caused by Pectobacterium carotovorum, Xanthomonas campestris pv. carotae, Meloidogyne javanica, Alternaria dauci, and Fusarium solani. ZnO at 0.10 mg/ml was the most effective treatment, reducing disease indices to 1 compared to the initial score of 4. These findings suggest that GO and ZnO NPs have promising potential as plant growth promoters and disease control agents for carrots, offering a sustainable approach to improving agricultural productivity and crop health.

Reference:

SIDDIQUI, Z.A., PARVEEN, A., AHMAD, L. AND HASHEM, A., 2019. Effects of graphene oxide and zinc oxide nanoparticles on growth, chlorophyll, carotenoids, proline contents and diseases of carrot. Scientia Horticulturae, 249, pp.374-382.