Pests and Diseases

Combining Silver Nanoparticles with Herbs Essential Oils to Control Plant Diseases

In a new and interesting study that has been done to find environmentally friendly ways to control plant diseases, Iranian researchers have achieved impressive results by combining essential oils and silver nanoparticles.

Essential oils (EOs) are unstable, aromatic liquids that naturally occur in various aromatic plant species. They can be harvested from such plants using different extraction techniques, including distillation and cold pressing. The EOs from one plant species can be very diverse: 20–60 (even up to over 100) volatile substances can be derived; however their concentrations in the plant materials vary greatly. EOs have a potential use in the ecofriendly management of plant diseases, because it has been demonstrated that they possess diverse biological activities, including inhibiting the growth of bacteria, fungi and yeast.

Based on studies and as an example for above mentioned effects of EOs, the phenolic monoterpenes “carvacrol” and “thymol” have been proven to be powerful, ecofriendly and effective agents with strong antibacterial, antifungal and insecticidal effects. These effects obviously depend on the type of mixture of chemical components in the pool of EOs, the chemical nature of the major components, and their functional groups. Moreover, synergistic interactions between some of the major and minor constituents may occur and such interactions may enhance the antimicrobial effects.

Researchers from the Islamic Azad University, Science and Research Branch of Tehran and the University of Kurdistan in collaboration with Wageningen University in the Netherlands have conducted a research study, the results of which have recently been published in an internationally accredited journal.

In this study, the effects of encapsulating essential oils from thyme and dill herbs in silver nanoparticles were investigated on the enhancement of the fungal activity of these EOs and control of anthracnose disease in the strawberry crop.

Anthracnose is a plant fungal disease that is caused in Iran by a fungus known as Colletotrichum nymphaeae. The disease can be seen in various crops, but in recent years, it has become a real epidemic in the strawberry fields of Kurdistan province.

To do this research, dill and thyme were cultivated in the experimental fields of Kurdistan Agricultural and Natural Resources Research Center. Dill seeds were harvested 15 weeks after planting, while thyme leaves were harvested 16 weeks after planting at flowering stage.

Researchers then identified below compounds as the main EOs for thyme based on mass gas chromatography: p-cymene, thymol, carvacrol and (E)-caryophyllene. They also recognized limonene, cis-dihydrocarvone, cyclohexanon, and carvone as the main essential oils for thyme.

After that, they encapsulated essential oils extracted from the dill seeds of thyme leaves in silver nanoparticles, using special techniques, and applied this compound to the fungus that causes anthracnose disease.

When the EOs of the two sources were encapsulated in silver nanoparticles, synergistic effects against C. nymphaeae were observed, resulting in more than 80% inhibition of mycelium growth of this pathogen. Moreover, conidia germination was suppressed by nano-encapsulated EOs. And considerable morphological changes in the fungal hyphae observed.

“Our study demonstrates the potential of encapsulated EOs in controlling pathogens that can be very applicable as antifungal agents”, reported by Weria Weisany, a researcher in the Department of Agriculture and Food Science, Islamic Azad University, Science and Research Branch of Tehran and other colleagues in this study.

They’ve mentioned: “Encapsulation in silver nanoparticles strongly improves the chemical stability of EOs when exposed to light, air, high temperatures and moisture. Furthermore, EOs from thyme and dill took longer to be released when they were encapsulated in silver nanoparticles than when they were not encapsulated. In our study, the use of nano-encapsulated EOs sustained and controlled the release of the active compounds and thus increased the bioavailability and usefulness against C. nymphaeae”.

The findings of this study suggest that nanotechnology can be considered as an eco-friendly strategy in plant disease management. This technology, in combination with existing practices, is able to improve the level of protection for agricultural and food products.

“Research into the effects of nanotechnology on the physiology of pathogens and their hosts, the infection process and the disease distinction and interactions can aid in extending novel approaches to management of plant diseases”, Weisany and colleagues believe. “In this regard, particular attention should be paid to the use of nanoparticles as pesticides that are less harmful to the environment than chemical ones”.

It should be noted that the above research findings are published in the journal “Industrial Crops and Products”. This international journal, published by Elsevier, has an impact factor of 4.191.

Author: Mohammadreza Delfieh

Industrial Crops and Products
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