Delivering Amendments to Plants — Via Needle

Increasing environmental conditions are pressuring the agriculture industry to adopt more sustainable and precise practices that foster more efficient use of resources and mitigation of environmental impacts. Developing delivery systems that efficiently deploy agrochemicals such as micronutrients, pesticides, and antibiotics in crops will help ensure high productivity and high produce quality while minimizing the waste of resources.

Current and standard practices for agrochemical application in plants, such as foliar spraying and fertigation, are inefficient due to off-target application, quick run-off in the rain, and the rapid degradation of active ingredients. These practices can also cause significant detrimental environmental side effects, such as water and soil contamination, biodiversity loss and degraded ecosystems, as well as public health concerns.

A novel silk-based microneedle technique developed by the Singapore-MIT Alliance for Research and Technology circumvents these limitations by deploying and targeting a known amount of payload directly into a plant’s deep tissues, leading to higher efficacy of plant growth and helping with disease management. The technique is minimally invasive; it delivers the compound without causing long-term damage to the plants and is environmentally sustainable. It minimizes resource wastage and mitigates the adverse side effects caused by agrochemical contamination of the environment. Additionally, it will help foster precise agricultural practices and provide new tools to study plants and design crop traits, helping to ensure food security.

Described in a paper published in the January 2023 issue of Advanced Materials, the research studies the first-ever polymeric microneedles used to deliver small compounds to a wide variety of plants and the plant response to biomaterial injection. Through gene expression analysis, the researchers could closely examine the reactions to drug delivery following microneedle injection. Minimal scar and callus formation were observed, suggesting minimal injection-induced wounding to the plant. The proof-of-concept provided in this study opens the door to plant microneedles’ application in plant biology and agriculture, enabling new means to regulate plant physiology and to study metabolisms via efficient and effective delivery of payloads.

The study optimized the design of microneedles to target the systemic transport system in Arabidopsis (mouse-ear cress). Gibberellic acid (GA3), a widely used plant growth regulator in agriculture, was selected for the delivery. The researchers found that delivering GA3 through microneedles was more effective in promoting growth than traditional methods (such as foliar spray). They then confirmed the effectiveness using genetic methods and demonstrated that the technique is applicable to various plant species, including vegetables, cereals, soybean and rice.

Professor Benedetto Marelli of MIT, co-corresponding author of the paper, shared, “The technique saves resources as compared to current methods of agrochemical delivery, which suffer from wastage. During the application, the microneedles break through the tissue barriers and release compounds directly inside the plants, avoiding agrochemical losses. The technique also allows for precise control of the amounts of the agrochemical used, ensuring high-tech precision agriculture and crop growth to optimize yield.”

“In the future, with automated microneedle application as a possibility, the technique may be used in high-tech outdoor and indoor farms for precise agrochemical delivery and disease management,” added Dr. Yunteng Cao of MIT.

Pesticides Could Be to Blame for Bland Strawberries

Have you ever bitten into a plump, red strawberry, only to find it bland and watery? Certain pesticides might be responsible. A team reporting in Journal of Agricultural and Food Chemistry has found that two common strawberry fungicides can impact cellular mechanisms, creating berries with subdued flavor and sweetness, as well as a lower nutritional value.

The flavor profile of any produce, including berries, is a result of its taste and smell — sweetness often arises from the amount of dissolved glucose or fructose, and a unique aroma comes from volatile compounds, such as esters and terpenes. In addition, many fruits are also full of nutrients, including vitamin C, folic acid and antioxidants. But because fungicides are designed to disrupt the cellular processes of detrimental fungi, they could accidentally interfere with these processes in crops, inhibiting production of these important flavor and nutritional compounds. So, Jinling Diao and colleagues wanted to investigate how two common pesticides used on strawberries — boscalid (BOS) and difenoconazole (DIF) — affect specific molecular pathways in berries.

The researchers grew three groups of strawberries (Fragaria x ananassa Duch) in identical conditions, applying BOS or DIF to two of the groups when the berries were still green. Even after treatment, the fully grown berries were identical in size and color to those grown without pesticide. Yet, under the surface, the team found a number of chemical changes caused by both of the fungicides:

• The levels of soluble sugars and nutrients, such as sucrose and vitamin C, were reduced.
• Sugars were converted into acids, further reducing sweetness.
• The amount of volatile compounds changed, subduing the berries’ taste and aroma.

Looking more closely, the team found that BOS had a direct effect on the regulation of genes involved in cellular pathways related to producing sugars, volatile compounds, nutrients and amino acids. Finally, in a blind taste test, people consistently preferred the untreated strawberries. The researchers say that this work could provide guidance to farmers about the use of pesticides.

Forecasting How Drain Tile Affects Nitrogen Loss

Midwestern agriculture contributes the vast majority of nitrogen in the Gulf of Mexico, causing an oxygen-starved hypoxic zone and challenging coastal economies. State and federal policies have tried for decades to provide solutions and incentives, but the hypoxic zone keeps coming back. A recent study from the University of Illinois, published in Water Research, offers a new way to understand Midwestern nitrogen dynamics and forecasts future nitrogen loads under various management scenarios across the region.

“Our model explains what’s going on across 83 watersheds in the Midwest, providing a quantitative understanding of why certain watersheds differ in terms of nutrient loss. But the most important contribution is our scenario prediction, which hasn’t been done before. If you increase tile drainage or the corn fraction, how much does the nitrogen load change? We can predict that, and I think that is really exciting,” said Kaiyu Guan, associate professor at the University of Illinois.

Guan said a more detailed understanding of nitrogen and water flow dynamics, as well as the ability to forecast the impact of management changes, is a critical step in developing effective policies for nutrient loss reduction from field to watershed scales.

The research team analyzed the relationship between daily flow rate and nitrate concentration across 83 Midwestern watersheds, finding a universal pattern throughout the region: nitrate increases with flow before leveling off at a high flow threshold.

“To further unpack this pattern, we built a simple yet elegant model that reveals the mechanism. We looked at the contributions of shallow soil water, which has a greater flow rate and more nitrate, and deep soil water, with a slower flow and lower nitrate,” said Zewei Ma, doctoral student in Guan’s group and first author of the study. “The contributions from these areas of the soil profile change depending on the tile drainage and how much corn is planted.”

Guan said the more tile drainage is installed and the more corn is planted in a given watershed, the greater the nitrate load in the water. That conclusion isn’t new, but the ability to forecast the impacts of increased tile installation or changing levels of corn is. The team created an interactive map to show how and where a 10 to 30 percent increase in tile or a 20 percent increase or decrease in corn will change nitrate loading.

“This model gives us a starting point for a meaningful discussion about ways to reduce nutrient loss: How we should invest our effort, and, just as importantly, where we should focus on reducing tile or changing the rotation pattern? These are key questions as we actively work towards nutrient loss reduction with farmers and policymakers,” said Bin Peng, a study co-author.

Study co-author Richard E. Warner adds, “This work offers a significant advance in our understanding of the variability in nutrient loss across watersheds and sets the stage for developing decision support tools that will help inform more cost-effective land and water conservation practices and policies.” 

Orchard Design Can Increase Pollination, and Thus Yield

To reduce biodiversity loss in agricultural landscapes, more sustainable and environmentally friendly agricultural practices are needed. A research team from the Universities of Göttingen and Hohenheim in Germany, and Venda in South Africa, investigated how ecosystem services such as pollination could be improved in macadamia plantations. The scientists showed that a certain design of plantations — for instance, how the rows of trees are arranged, the varieties, and the integration of semi-natural habitats in and around the plantations — can increase the pollination performance of bees. The results were published in the Journal of Applied Ecology.

The research team first investigated the role of insect pollinators in the nut production of macadamia trees. “Insect pollination of macadamia flowers is essential for production. A complete loss of insect pollinators would reduce the amount of nuts by 75 percent,” said Professor Ingo Grass of the University of Hohenheim. 

To find out which conditions encourage pollinators, the researchers observed and counted the bees and other insects on the macadamia flowers. “Surprisingly, it is less important how many honeybee colonies were established in the vicinity. The more important factor is how large the proportion of semi-natural habitats is in the vicinity of the plantation, since the majority of pollinators fly from the semi-natural habitats into the plantations,” said first author Mina Anders.

The arrangement of the rows of trees in the plantations is therefore particularly important: 80 percent more nuts grew at the edge of the plantation — i.e., land that borders on semi-natural habitats — than in the middle of the plantation. Directly after flowering, the nut formation increased more than threefold in tree rows planted at right angles to semi-natural habitats, compared to rows planted parallel to the habitats. “Pollinators move more easily from their habitat to the plantations when the rows are perpendicular, as they prefer to fly along the rows rather than through them,” Anders explains. Agronomic practices such as artificial irrigation, on the other hand, did not increase the initial nut formation.

“Given the urgency to reduce the harmful environmental impacts of agricultural practices, we emphasize the enormous potential of supporting ecology through intelligent plantation design and the restoration and maintenance of semi-natural habitats in plantations and the surrounding landscape,” said Professor Catrin Westphal.

Restricting Antibiotics for Livestock Could Limit Spread of Antibiotic-Resistant Infections in People

A California policy restricting antibiotic use in animals raised for food is associated with a reduction in one type of antibiotic-resistant infection in people in the state, according to a new study published in the journal Environmental Health Perspectives.

The results suggest that regulations limiting antibiotics in livestock can significantly impact human health.

In 2018, California Senate Bill 27 (SB27) banned, for the first time in the U.S., routine preventive use of antibiotics in food-animal production and any antibiotic use without a veterinarian’s prescription.

The researchers found that the policy was associated with a 7% reduction in resistance to one class of antibiotics used in livestock, extended-spectrum cephalosporins, among Escherichia coli bacteria isolated from urine in people with urinary tract infections.

“After climate change, antibiotic resistance is the second biggest public health problem we’ll be facing in the next 50 years, because few new antibiotics are coming online and resistance is increasing,” Dr. Joan Casey of Columbia University said. “Anything we can do that reduces resistance is really exciting.”

“Reducing antimicrobial resistance is a critical factor in improving community health,” said Sara Tartof, an epidemiologist with Kaiser Permanente Department of Research & Evaluation in Southern California. “This study shows that changes in clinical practice alone will not be sufficient to reduce this threat. We need to strengthen our efforts with larger public policy initiatives to reduce antimicrobial use beyond the hospital setting as well.”

Researchers have previously demonstrated links between the widespread use of antibiotics on livestock and antimicrobial-resistant infections in people, which cause nearly three million infections and 35,000 deaths each year.

Antimicrobial-resistant pathogens can spread from livestock to people through contaminated meat, environmental pathways such as water and air, and exposures among people working in livestock operations or living near them.

To test the impact of the new legislation on antibiotic-resistant infections in people, the research team examined data on antibiotic-resistant E. coli in 7.1 million urine samples from people with urinary tract infections across 33 states from 2013 to 2021.

“In an ideal world, we’d have two Californias and we would observe both of them over time, but we don’t have one of them,” Casey explained. “We used statistical methods to create this dream, synthetic California” in which the bill had not been passed.

With this approach, called the synthetic control method, they first used a composite of data from states that did not have the policy change to match the patterns of antimicrobial resistance in California before the bill passed.

Then they compared the levels of four different antibiotic-resistant E. coli in the California samples to the corresponding levels in their “synthetic California” data before and after the bill passed.

“We saw a reduction in the actual California versus our synthetic California for one of the antibiotic classes that we hypothesized could be linked to on-farm antibiotic use,” Casey said.

That class, extended-spectrum cephalosporins, is used in raising both cattle and poultry. Though it represents less than 1 percent of U.S. antibiotic sales for livestock, 80 percent of these sales are for use in cattle, one of the most common food animals raised in California.

The researchers found no change linked with the bill in resistance patterns for three other classes of antibiotics: tetracycline, which is used in both livestock and humans, and aminoglycoside and fluoroquinolones, which are used only in humans.

Interpreting the results is complicated by the fact that California has not made data for on-farm antibiotic use public, despite being required to do so by SB27.