Groundbreaking research has demonstrated in the lab how infected mother plants can prevent the transmission of their virus to the seeds of future seedlings through a genetically defined process of immunosuppression aimed at blocking vertical transmission.
The long-standing practice of monoculture – and more recently, industrial agriculture – has led to a range of global consequences for the environment and biodiversity. The intensive cultivation of single plant species over large areas not only depletes soil quality and increases atmospheric carbon dioxide concentrations over time, but also makes crops more vulnerable to a variety of pathogens [source: “Monoculture” – Science Direct].
In this context, a 2021 study by the Institute of Agriculture at the University of Western Australia (“Global Plant Virus Disease Pandemics and Epidemics” – Plants) highlighted that nearly half (47%) of pathogens causing infectious diseases in plants worldwide are viruses. Known as “phytoviruses,” these viruses attack plants, including fruit and vegetable crops, in a manner similar to how viral infections affect humans, by invading cells, destroying them, and triggering disease outbreaks.
Beyond monoculture and intensive farming, the study’s author points out that «the global worsening of plant viral diseases in the last decade has primarily been driven by the expansion of international trade in plant products, including seed trade. This has introduced harmful phytoviruses to regions where they were previously absent». Let’s take a closer look.
TAKEAWAYS
Major epidemic and pandemic plant viral diseases
Plant infectious diseases are an ancient and evolving phenomenon. The first phytovirus was described in 1892 by Russian botanist and biologist Dmitrij Ivanovsky, who identified the “Tobacco Mosaic Virus” (TMV). This virus infects numerous plant species, including beets, cucumbers, maize, potatoes, and peas, causing a characteristic yellow “mosaic” pattern on the leaves [source: “Plant virology” – National Library of Medicine].
Since then, research has focused particularly on infections that cause severe diseases in plants, especially those used for human and animal consumption. The previously mentioned University of Western Australia study lists the main examples of epidemic plant diseases, which occur «when a disease spreads over an area where its causal agent has long been present». These include:
- wheat disease caused by Barley Yellow Dwarf Virus
- wheat streak mosaic disease, induced by a virus from the Potyviridae family
- ring spots and warts on tubers, linked to Tobacco Rattle Virus
- faba bean necrotic yellows, originating from Broad Bean Wilt and Allied Viruses
- tomato disease caused by Pepino Mosaic Virus
- tomato brown rugose fruit disease, associated with Tomato Brown Rugose Fruit Virus
- cucumber disease caused by Cucumber Mosaic Virus
The study also identifies six major examples of pandemic plant diseases, which occur «when epidemics cause mass infections across different continents»:
- maize lethal necrosis, caused by the interaction between Maize chlorotic mottle virus (MCMV) and a virus from the Potyvirus genus
- rice tungro, triggered by the combination of two viruses transmitted by leafhoppers
- potato Virus Y
- banana bunchy top disease, characterised by dense foliage and no fruit, caused by Banana Bunchy Top Virus
- citrus tristeza, a disease caused by Citrus Tristeza Virus
- sharka, or plum pox, «affecting stone fruit trees such as peach, plum, apricot, almond, and cherry», caused by Plum Pox Virus

Plant viruses on the rise
The article “The Persistent Threat of Emerging Plant Disease Pandemics to Global Food Security” by Kansas State University, published in PNAS – Proceedings of the National Academy of Sciences, highlights the increasing occurrence of viral plant disease epidemics in many regions worldwide, particularly in socio-economically vulnerable areas. These epidemics threaten food security by reducing crop yields.
«When a large number of plants are systematically infected by a virus, and the infection spreads to the point of causing a viral pandemic or major epidemic in staple crops, the risk is a significant reduction in food supplies, leading to severe shortages.» It is estimated that in 2014, plant viral pandemics and epidemics caused a global economic impact exceeding $30 billion annually. Ten years on, «their current economic impact has grown considerably, driven by the intensification of global agriculture and the increasing demand for plant-based products to feed a rapidly expanding population» [source: “Crop losses caused by viruses” – Crop Protection].
Looking at recent developments, in April 2024, the rapid spread of the “Cacao Swollen Shoot Virus” (CSSV) was reported in Ghana and other West African countries, posing a significant threat to cocoa production, with farmers facing potential yield losses ranging from 15% to 50%.
In July 2024, the Regional Phytosanitary Service of Sardinia detected Citrus Tristeza Virus (CTV) in the Citrus reticulata Valley Gold orchard area, subsequently quarantining the affected territory.
Another significant example is the previously mentioned “sharka” disease, the most severe viral disease affecting stone fruit trees such as peach, plum, apricot, almond, and cherry. Unfortunately, it is present in Italy and many other countries worldwide.
Mechanisms of plant-virus interaction
The processes that govern the interaction between a host plant and a virus determine the development of symptoms in the infected plant. These symptoms can manifest externally through changes in the size of its structure, leaves, and fruits, or appear as spots, discoloration, streaks, warts, and roughness. Internally, symptoms may include changes in the flavour of the fruit and the texture of the flesh, potentially leading to a complete absence of leaves and/or fruit.
In response to viral infection, plants deploy their immune system through a range of antiviral defence mechanisms, classified as “passive” and “active.” Passive defences involve «the plant’s failure to produce one or more factors required for virus replication». Active defences, on the other hand, include «detecting and eliminating the virus through gene silencing via RNA interference» [source: “Plant virus” – Science Direct]. “RNA interference” refers to «a biological response capable of silencing gene expression across a wide range of organisms, including pathogens» [source: “RNA Interference: Biology, Mechanism, and Applications” – National Library of Medicine].
RNA (RiboNucleic Acid) is a molecule present in the cell nucleus, alongside DNA, and is «involved in various biological roles, such as gene coding, regulation, and expression, particularly in protein synthesis».
It is important to note that during transmission to a new host (another plant), «viruses rely on specific proteins that modify the structural components of the cell to enable the transport of viral proteins and genetic material into another plant» [source: “The molecular mechanism of efficient transmission of plant viruses in variable virus–vector–plant interactions” – Science Direct, 2021].
Understanding the dynamics of plant-virus interactions is essential for gaining deeper insights into the evolutionary nature of phytoviruses and their transmission mechanisms.
The team behind the study “Antiviral RNA Interference Inhibits Virus Vertical Transmission in Plants” (Cell Host & Microbe, September 2024), composed of researchers from the Institute for Integrative Genome Biology at the University of California, Riverside, also emphasizes seed trade as a primary pathway for the spread of plant viral infections from one country to another. The researchers note that seeds can be infected due to viral transmission from the “parent,” or “mother plant,” through what is referred to in genetics as “vertical transmission“.
Vertical transmission of phytoviruses
«Phytoviruses passed from parent to offspring can remain dormant within the seeds of future young plants for years, only to suddenly manifest with characteristic symptoms» observes the Californian research team. This poses a significant global concern for farmers.
In mammals, including humans, vertical transmission of viral agents, such as HIV (Human Immunodeficiency Virus), is rare, «likely due to various antiviral immune mechanisms, including passively transferred maternal antibodies».
In contrast, vertical transmission of plant viruses via seeds is more common, although often at very low rates (but still sufficient, given the vast number of seeds traded globally, to infect entire crops).
«For instance, when a mother plant affected by a virus produces 100 seeds, only 0 to 5% of the seedlings may be at risk of infection. For a century, scientists have wondered how this occurs, that is how mother plants can prevent the virus from spreading to all or most of the young plants». This question formed the basis of the research conducted by the University of California scientists.
The study involved an experiment on hundreds of varieties of a small mustard family plant, Arabidopsis thaliana, in which the Cucumber Mosaic Virus (CMV) – capable of infecting over a thousand different plant species – was introduced. The virus’s symptoms include yellowing, ring-shaped spots, and markings on the surfaces of leaves and fruits.
The aim was to observe and analyse the plants’ responses to discover which genes make both the plants and their offspring more resistant to the CMV virus.
The immune pathway that prevents virus transmission from mother-plant to the offspring
During the examination of the immune response in one hundred varieties of Arabidopsis thaliana, the research team focused specifically on the role of two genes, which play a central role during the early stages of seed development and are especially active in antiviral defence. The researchers found that these genes are also involved in RNA interference, a biological response that silences gene expression across a wide range of organisms, including pathogens.
How exactly does this interference work? The authors explain:
«The genetic information contained within cells – where a virus might also reside – is transferred from DNA to RNA and then to proteins. This is the process of protein synthesis. Occasionally, during this process, the double-stranded RNA is cut, and its smaller fragments, known as siRNA (short interfering RNA), are used to ‘interfere’ with the described synthesis, blocking the production of proteins, some of which could originate from the invading virus»
Many plants, they add, produce short interfering RNA specifically to control and inhibit viral infections. These same plants can prevent infections in seeds «because the antiviral RNA interference is already active as the seeds develop within the mother plant». This was the discovery.
To validate this hypothesis, the team created “mutant plants” in the laboratory, lacking two key genes involved in RNA interference. These genes are responsible for producing two plant enzymes, known as dicer-like 2 and dicer-like 4, which are essential for the production of siRNA needed to inhibit viral infections.
In essence, the researchers demonstrated their theory by engineering plants that lacked any antiviral immune pathways. The findings were conclusive:
«The mutant plants grew and produced seeds normally. However, when they were inoculated with the Cucumber Mosaic Virus, they exhibited severe symptoms. They began to produce fewer seeds, and, crucially, the rate of virus transmission to the seeds increased tenfold compared to non-mutant Arabidopsis thaliana varieties, with up to 40% of the new seedlings being infected»
Glimpses of Futures
This research has shown that an infected plant can, through a genetically defined immunosuppressive pathway for vertical transmission, prevent the virus from being passed on to the seeds of future plants. The focus is on the role of RNA interference in plants, specifically aimed at silencing viral infections.
To anticipate possible future scenarios, let us now analyse – using the STEPS framework – the potential impacts that the evolution of this immunosuppressive strategy (enhanced by biotechnologists) could have in social, technological, economic, political, and sustainability terms.
S – SOCIAL: plant viruses are a scourge for agriculture, including horticulture and fruit farming. Their transmission through seeds promotes transcontinental spread and acts as a source of infection capable of triggering devastating epidemics and pandemics in crops. In a future scenario, if the RNA interference-based immunosuppressive pathway in plants were to become a well-established strategy beyond research laboratories, it could suppress virus transmission to seeds (the progeny of infected plants), resulting in healthier and more robust harvests. Moreover, since RNA interference functions as an active antiviral response in mammals as well, the discovery by the Institute for Integrative Genome Biology at the University of California, Riverside, could pave the way for new research into vertical virus transmission in humans, from mother to fetus.
T – TECHNOLOGICAL: utilising genetic engineering and biotechnology techniques, it will be possible in the future to further reduce the transmission rates of the virus studied by the Californian researchers (Cucumber Mosaic Virus – CMV) by strengthening the identified immune pathway in seeds, starting from the moment they develop within the mother plants. As mentioned, since this pathway exists in a range of organisms, including invertebrates, fungi, and mammals, the discovery could also have positive implications for disease prevention research in both animals and humans. In particular, the Californian researchers suggest a potential future intervention targeting the human Zika virus, transmitted via the bite of infected mosquitoes and related to viruses such as yellow fever, dengue, Japanese encephalitis, and West Nile encephalitis. If present, even latently, in the mother’s body, Zika «can cause severe birth defects during pregnancy, including microcephaly and other brain abnormalities». The insights gained regarding the vertical transmission of CMV could support the international scientific community in reducing the vertical transmission rate of Zika: «We know that this virus expresses various proteins that block the RNA interference pathway, so it could be possible to prevent vertical transmission by developing targeted drugs to inhibit the function of these proteins».
E – ECONOMIC: the socio-economic impact of the findings becomes evident when considering the economic data on the global effects of plant viral diseases. The American Phytopathological Society notes that phytoviruses cause yield losses of up to 40% in major crops (including maize, rice, and wheat), resulting in annual global economic losses of approximately $220 billion. “The most destructive and widespread viruses, which pose a global threat to humanity, lead to significant yield reductions in fifteen different crops, including wheat, barley, maize, potatoes, sugar beet, tobacco, and cotton” [source: Economic significance of viruses in field crops – Viral Diseases of Field and Horticultural Crops, 2024].
P – POLITICAL: in a future where the evolution of the immunosuppressive pathway highlighted by the authors—along with the use of genetic engineering and biotech techniques—enables the enhancement of immune response mechanisms in plants to reduce or even eliminate phytovirus transmission rates, careful attention must be given to risk assessment oversight. This is crucial for ensuring food safety, as well as safeguarding human health and the environment, as with all recent scientific advancements in genetics applied to areas affecting human life, especially those concerning the food and nutrition sector. On this note, it is worth recalling that on 24 January 2024, the European Parliament’s Committee on the Environment, Public Health, and Food Safety approved a legislative proposal on the production of agricultural plants derived from the use of genetic scissors. This was considered a historic milestone for food, environmental, social, and economic sustainability in the European Union.
S – SUSTAINABILITY: identifying and reconstructing the immunosuppressive pathway that allows an infected mother plant to prevent its virus from being transmitted to the seeds of future plants is significant for food, environmental, social, and economic sustainability. This discovery points towards a future where it could be possible to eliminate plant viral epidemics and pandemics (and reduce the need for chemical treatments to combat them) along with associated food shortages, thereby enhancing global food security and meeting the rising demand for plant-based products needed to feed the rapidly growing population. The populations of the poorest countries will be the primary beneficiaries of the potential future advancements in the immunosuppressive mechanism identified by the research team.