Eco-update

New Natural Defense against Citrus Greening and Other Diseases

Texas A&M AgriLife Research scientists have developed a new approach to countering citrus greening and potato zebra chip diseases, two economically devastating agricultural diseases in the U.S. Their method uses spinach antimicrobial peptides, known as defensins, which naturally defend plants against a broad range of pathogens.

In a recent study published in the Plant Biotechnology Journal, researchers showed that some spinach defensins can confer similar protection to citrus and potatoes — and possibly other crops. The effects show significant progress toward recovering yield and improving quality in diseased plants.

The team chose spinach antimicrobial peptides after learning from previous studies that they can fend off various pathogenic fungi and bacteria. Because these peptides occur naturally in spinach, they’re also frequently safely consumed by humans.

The researchers delivered the peptides to commercial citrus trees using a benign virus. The virus naturally infects the trees in the same location where the disease-causing bacteria reside. Using a simple grafting procedure, the researchers were able to apply the virus and allow it to deliver the peptides targeting the bacteria largely on its own.

Over a few years, the research team monitored how citrus trees infected with Candidatus Liberibacter asiaticus, the bacterium responsible for citrus greening, responded to treatment with specific antimicrobial peptides. They saw promising results, including up to 50 percent increases in fruit yield compared to untreated trees after only a single application.

Additionally, the researchers explored how the spinach peptides might enhance the immune response against Candidatus Liberibacter solanacearum. This bacterium is related to the citrus greening pathogen and causes zebra chip disease in potatoes and other vegetables.

When researchers expressed the antimicrobial peptides in potatoes, the potato plants showed minimal disease symptoms, had less disease-causing bacteria present, had much less of the characteristic zebra chip discoloration in tubers, and had greater tuber numbers compared to untreated plants.

Altogether, the team’s results show encouraging effects for the two spinach antimicrobial peptides added independently to citrus and potatoes. The researchers envision creating “cocktails” of multiple peptides and exploring the effects when combined with other integrated management strategies to control the insects spreading the bacteria as well.

Not Natural: Common diabetes drug helps chickens lay more eggs

Penn State researchers have discovered that metformin, a drug usually prescribed for type-2 diabetes and polycystic ovary syndrome (PCOS) in humans, can actually help chickens lay more eggs. Specifically, it helps broiler breeder hens stay fertile and produce eggs for longer, even as they age.

Broiler breeder hens have been selectively bred for decades for their offspring to grow quickly and reach market weight fast. But as these birds age, their ability to lay eggs declines rapidly, limiting how long they can remain productive. This drop in fertile egg production resembles PCOS in humans, which also affects fertility and ovarian function. 

PCOS, a hormonal disorder affecting women characterized by irregular menstrual cycles, is the most widespread endocrinological condition, affecting roughly 4 to 12 percent of women, and is the main cause of infertility in women, according to the National Institutes of Health. Metformin is often used off-label to treat PCOS symptoms, improving insulin sensitivity, lowering excess hormone levels and helping to regulate menstrual cycles, potentially aiding fertility.

In a 2023 study, researchers at Penn State gave a group of hens a small daily dose of metformin over 40 weeks. The results were striking: the hens laid more fertile eggs, had lower body fat and showed healthier reproductive hormone levels than those not given the drug.

The researchers then dug deeper to find out what exactly was happening inside the birds’ bodies — and they found the answer in the liver. The liver plays a key role in bird reproduction — it’s where egg yolk precursors are made. Using advanced gene sequencing techniques, the team analyzed RNA from liver samples and discovered that metformin “switched on” several genes involved in producing yolk proteins and maintaining stable blood sugar. At the same time, it “switched off” genes linked to fat buildup — mirroring how metformin works in humans with metabolic disorders.

“Essentially, metformin helps older hens stay metabolically healthier, which lets them keep producing eggs well beyond their usual decline,” said Evelyn Weaver, a lead author of the study. Metformin is quickly metabolized by these hens, Weaver pointed out, so it poses no risk of entering the human food supply.

About that Metformin: Inactive Components in Agricultural Runoff May Be Hidden Contributors to Drinking Water Hazards

Inactive ingredients in agricultural, pharmaceutical and other common products have typically been excluded from consideration as potential contaminants in drinking water. However, while these chemicals are inert in certain products, they still can pose hazards when combined with other materials during the drinking water treatment process.

A new study from researchers at Washington University in St. Louis reveals how large this impact might be. The researchers examined the use of amines in herbicides and their potential role as precursors to nitrosamines, harmful byproducts formed during water disinfection. They discovered that inactive amines, which are used as stabilizing agents in herbicides to increase solubility and reduce drift, may be more important than active agents in herbicides when it comes to forming disinfection byproducts linked to various health risks, though the impacts vary by region and time. The results were published in the April 15 issue of Water Research.

The researchers compared the annual use of amines in herbicides to other known nitrosamine precursors, such as the widely used pharmaceuticals ranitidine and metformin. They found that the use of amines in herbicide formulations has increased in recent decades, particularly affecting certain regions including the Midwest.

Because of the quantity of amines used, these inactive agents are potentially much more important nitrosamine precursors than researchers previously thought. Amines from herbicides have the potential to enter the environment at rates similar to precursors from pharmaceuticals. This could have significant implications for water treatment processes, as nitrosamines are known to pose serious health risks even at low concentrations.

New Study Unlocks How Root Cells Sense and Adapt to Soil

Scientists have discovered, for the first time how root cells respond to their complex soil environment revealing that roots actively sense their microenvironment and mount precise, cell-specific molecular responses. 

In a study published in Nature, the team used cutting-edge spatial and single-cell transcriptomics to compare rice roots grown in conventional gel-based media with those grown in heterogeneous natural soils and hard soils.

One striking discovery involved the hormone abscisic acid (ABA), known for its role in water stress. The study showed ABA helps reinforce waterproofing barriers, reducing water loss from roots and aiding their resilience to hard soils. 

Soil is a dynamic ecosystem that is far from uniform: it presents a constantly changing mosaic of nutrients, water availability, microbial life, and mechanical challenges for plants. “Seeing genes related to nutrient sensing, water response, and biotic stress light up ONLY in soil-grown roots was awe-inspiring” said first author Mingyuan Zhu. “It was a striking moment that made the complexity of root-soil environment interactions feel vividly real.”

The study showed that the activation of plant response systems is not only regulated by genetic or biochemical process, but one that physically changes the plant’s material properties on a cellular level. The team used a new cellular resolution imaging technology called phonon microscopy to map changes in cell wall stiffness for roots grown in stressed and unstressed environments.

“We have discovered this incredible capability for plant roots to effectively ‘brace for impact’ by stiffening their cell walls, when grown in soil that has been compacted,” said Dr. Salvatore La Cavera. 

Insecticides May Contribute to Bigger Problems with Certain Weeds

Insecticides may help growers hoping to protect their crops from harmful insects, but they may also contribute to a larger amount of some weeds, according to a study led by researchers at Penn State.

The study — published in the journal PeerJ — compared using insecticides preventively at planting versus using an integrated pest management (IPM) approach, which calls for insecticides only when a known insect problem exists. The team also investigated the effects of using cover crops when combined with these treatment plans.

The researchers found that by the third year, some fields that were treated with insecticides and didn’t have a cover crop ended up with slightly more weeds — especially marestail. However, planting a cover crop prevented this issue, even in fields that were treated with insecticides. 

The most likely explanation may be that the preventative insecticides limited the activity of insects that typically eat weeds or weed seeds, allowing the weeds to be more abundant. Insects such as beetles, ants and crickets eat weed seeds. Insecticides may affect these beneficial insects in addition to pests, interfering with their ability to eat these seeds and control weed populations.

Even Sublethal Insecticide Dose May Disrupt Pollinator Mating Process

Insecticides can help protect crops against troublesome pests, but they also pose a risk for beneficial insects such as pollinators. A new study led by researchers at Penn State provided insight into how even sublethal doses of insecticides can negatively affect pollinators by disrupting the mating process. The study, published in the journal Science of the Total Environment, looked at the effects of imidacloprid, a neonicotinoid that is among the most widely used insecticides globally.

The researchers found that exposure to the insecticide, even at sublethal levels, reduced successful mating in bumblebees and altered the chemical signaling of both males and gynes — female bees capable of reproduction. It also negatively impacted both sperm viability in males and lipid storage in gynes.

After pesticides are applied to seeds or plants, these chemicals persist in the soil, pollen and nectar, giving pollinators multiple routes of exposure. To examine the effects of imidacloprid on bee mating behavior, the researchers exposed bumblebees to very low concentrations of the insecticide in a lab. They gave bees access to sugar water that contained either six or 60 parts per billion of imidacloprid for three days, concentrations that mimicked what they might encounter in the wild.

Next, the researchers took gynes that either had been exposed to the insecticide or not exposed and placed them with male bees to examine whether the exposure affected their mating process. The researchers then flipped the experiment — placing males that either were exposed or not exposed with female bees.

The team also wanted to know if exposure to pesticides could alter chemical signaling, so the researchers measured potential sex pheromone compounds from the body surface of both males and gynes and from glands that produce pheromones. Finally, they measured sperm viability in males and the fat reserves of gynes. Gynes rely on fat reserves to survive the winter.

After analyzing the data, the researchers found that exposure to the insecticide seemed to have a stronger effect on female bees. Gynes had similar pesticide levels in their bodies as males did despite being more than three times larger on average, and while males avoided the insecticide-treated gynes, the gynes didn’t avoid treated males. Still, males were affected by exposure to imidacloprid, which reduced the total amount of sperm and sperm viability in the 60 parts per billion group by 41 and 7 percent, respectively.

The findings add to growing concerns about the effects of neonicotinoids on pollinator health. While metrics such as survival and reproduction provide a useful starting point for evaluating the ecological damage caused by pesticides, they likely represent only the tip of the iceberg.