- Author: Ben Faber
Reactive oxygen species (ROS) cause oxidative stress at the cellular level. Research shows that this way, amongst others, they inhibit the germination capacity of plants, produce cytotoxins or exert toxic effects on aquatic invertebrates. Environmentally persistent free radicals (EPFR) are potential precursors of ROS because they can react with water to form these radical species. "Therefore, EPFR are associated with harmful effects on the ecosystem and human health," explains Gabriel Sigmund, the lead investigator of the study.
"Our study shows that these environmentally persistent free radicals can be found in large quantities and over a long period of time in fire derived charcoal," reports Sigmund, environmental geoscientist at the Center for Microbiology and Environmental Systems Science (CMESS) at the University of Vienna. In all 60 charcoal samples from ten different fires, the researchers detected EPFR in concentrations that exceeded those typically found in soils by as much as ten to a thousand times. Other than expected, this concentration remained stable for at least five years, as an analysis of charcoal samples showed which were gathered at the same location and over several years after a forest fire. "The more stable the environmentally persistent free radicals are, the more likely it is that they will have an impact on ecosystems over longer periods of time," explains Thilo Hofmann, co-author of the study and head of the research group.
Samples from fires in forest, shrubland and grassland spanning different climates
The researchers collected charcoal samples from fires of diverse intensity in boreal, temperate, subtropical, and tropical climates. They considered forest, shrubland and grassland fires and, thus, also different fuel materials (woods and grasses). The original material and the charring conditions determine the degree of carbonization. Consequently, both indirectly influence the extent to which EPFR are formed and how persistent they are. "The analyses show that the concentration of environmentally persistent free radicals increased with the degree of carbonization," Sigmund reports. Woody fuels favored higher concentrations. For these, the researchers were also able to demonstrate the stability of EPFR over several years. "We assume that woody wildfire derived charcoal is a globally important source of these free radicals and thus potentially also of harmful reactive oxygen species," adds Hofmann.
International collaboration across disciplines
"It is our collaboration with colleagues at Swansea University in the United Kingdom that enables us to make these highly differentiated statements," explains Sigmund. The wildfire experts at Swansea University are conducting global research into the effects of fire on environmental processes such as the carbon cycle and erosion. They have collected charcoal samples from around the world and sent them to Vienna for analysis, along with information on the timing, duration and intensity of the fires. CMESS researchers analyzed the samples in collaboration with Marc Pignitter of the Faculty of Chemistry using electron spin resonance spectroscopy (ESR spectroscopy). ESR spectroscopy made it possible to quantify the environmentally persistent free radicals in the studied material and to identify their adjacent chemical structures.
Questions about consequences for the ecosystem
The study has provided insights, but also raised further questions: The fact that environmentally persistent free radicals occur in such high concentrations and remain stable over several years was surprising. In future studies, the researchers are planning to also assess the consequences this may have for the environment. "To what extent is this a stress factor for microorganisms after a fire? How does it affect an ecosystem? The study is an impetus for further research," reports Sigmund.
G. Sigmund, C. Santín, M. Pignitter, N. Tepe, S. H. Doerr, T. Hofmann, Environmentally persistent free radicals are ubiquitous in wildfire charcoals and remain stable for years. Communications Earth & Environment (2021),
https://www.nature.com/articles/s43247-021-00138-2
- Author: Ashley Robinson
The Australian finger lime, a citrus relative, could be a new specialty crop for Florida citrus growers.
Traditionally, finger limes have remained rare in the United States, grown few and far between. However, the fruit's unique tolerance to HLB is becoming increasingly attractive to Florida growers. Manjul Dutt, research assistant scientist at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) believes finger limes could secure Florida's position in the global citrus market.
In the field, finger limes have a low HLB infection rate. Early on, researchers noticed these trees were much more tolerant to HLB than any of the traditional citrus varieties being grown in the state.
“We have a number of theories as to why this finger lime could be tolerant to HLB,” Dutt says. “It could be due to the presence of physical barriers, or it could be due to the presence of certain toxins or certain chemicals in the phloem that the Candidatus Liberibacter asiaticus' (CLas) doesn't like.” CLas is the bacterium that causes HLB.
The young flesh of finger limes contains high levels of anthocyanins, producing a dark-red color on the leaves of the tree. Studies have indicated that insects, including the Asian citrus psyllid, move according to visual cues. It's possible the high levels of anthocyanins can discourage psyllid feeding and thus prevent transmission of HLB.
Additionally, the phloem of the finger lime contains high levels of aldehyde compounds. According to Dutt, citronellol, a compound of growing interest and present in the phloem, has shown to have anti-bacterial activity, which could also be preventing the replication of CLas.
One of the pressing issues limiting commercial production of finger limes in Florida is the lack of knowledge about the crop. Dutt and his team of researchers are currently evaluating different rootstocks in hopes of finding varieties suitable for Florida's growing conditions.
Furthermore, they are developing new cultivars that are crosses between conventional citrus and finger limes to incorporate HLB tolerance into traditional citrus varieties. Dutt says thousands of trees are currently being evaluated and quite a few appear promising
Tapping into their genetics
While finger limes aren't exactly set out to be the new crop replacing Florida's longstanding orange and grapefruit industry, Dutt believes finger lime trees can provide a strong assist. “Hybrids between finger limes and sweet orange down the road may have sweet orange-like traits that can be acceptable to the grower and consumer. It would create a sweet orange-like fruit with finger lime genetics that allow it to be tolerant to HLB,” he says. “Many people in the industry realize it's a long-term process. Some are skeptical but overall, people are hopeful that the finger-lime genetics play an important role in providing HLB-tolerant trees in the future.”
To date, finger limes are more of a niche crop in North America with only a few growers in California, Hawaii and Florida.
In the meantime, Dutt has produced a finger lime hybrid that looks like a larger finger lime. “We'll be releasing it this summer—it's similar to the finger lime but it has more pulp and the same “pearls” that finger limes do,” he says. He adds that it's a commercial release as a niche crop and hopes the limes will be available in stores in the next three to four years
For more information:
Dr. Manjul Dutt
University of Florida
Tel: +1 (863) 956-8679
manjul@ufl.edu
https://crec.ifas.ufl.edu/
- Author: Jules Bernstein
https://news.ucr.edu/author/jules-bernstein
New research reveals an essential step in scientists' quest to create targeted, more eco-friendly fungicides that protect food crops.
Scientists have known for decades that biological cells manufacture tiny, round structures called extracellular vesicles. However, their pivotal roles in communication between invading microorganisms and their hosts were recognized only recently.
UC Riverside geneticist Hailing Jin and her team found plants use these vesicles to launch RNA molecules at fungal invaders, suppressing the genes that make the fungi dangerous.
“These vesicles shuttle small RNAs between cells, like tiny Trojan horses with weapons hidden inside,” said Jin, a professor of genetics and the Cy Mouradick Chair in the Department of Plant Pathology and Microbiology. “They can silence pathogenic fungal gene expression.”
Using extracellular vesicles and small RNAs has several advantages over conventional fungicides. They're more eco-friendly because they are similar to naturally occurring products. Eventually, they degrade and do not leave toxic residues in the soil. Also, Jin explained, this method of fighting fungi is less likely to breed drug-resistant pathogens.
A sticking point for scientists in creating these fungicides has been figuring out how to load their desired small RNAs into the vesicles.
“We've wondered how these weaponized small RNAs get into the bubbles,” Jin said. “Now, we think we have an answer.”
Her laboratory has identified several proteins that serve as binding agents, helping to select and load small RNAs into the vesicles. The lab's research is detailed in a new Nature Plants journal article.
The Jin laboratory has been working for several years on the development of gene-silencing RNA fungicides. Work toward this goal led to the team's landmark discovery in 2013 that gene-silencing RNA messages can be sent from the fungal pathogen to the plant host to suppress host immunity. Later, the team learned small RNAs can move both ways — from plants into pathogenic invader cells as well. In 2018, the team worked out that extracellular vesicles were the major delivery system for these small RNAs. They observed that Arabidopsis plants secrete extracellular vesicles into Botrytis cinerea, a fungus that causes grey mold disease and destroys millions of crops every year.
“This was the first example of a host using these vesicles to deliver small RNAs to another organism,” Jin said. “Previously we saw movement of RNA, but didn't know how the small RNA are selected and transported.”
Now, she and her colleagues have identified several RNA-binding proteins in Arabidopsis that bind to specific small RNA molecules and load them into extracellular vesicles. This suggests the proteins play an important role in loading and stabilizing small RNAs in the vesicles. The finding can help increase the payload of gene-silencing RNAs that make it into vesicles and enhance the efficiency of disease control.
Some scientists have taken inspiration from the RNA communication in plant vesicles to design human therapies. For example, some are attempting to load anti-cancer RNAs and drugs into extracellular vesicles in fruits or vegetables, so people can eat or drink them. Jin is hopeful that her lab's discovery can aid these efforts.
- Author: Jules Bernstein
https://news.ucr.edu/author/jules-bernstein
UC Riverside scientists are betting an ancient solution will solve citrus growers' biggest problem by breeding new fruits with natural resistance to a deadly tree disease.
New hybrid citrus fruit bred for disease resistance and flavor. (Chandrika Ramadugu/UCR)
The hybrid fruits will ideally share the best of their parents' attributes: the tastiness of the best citrus, and the resistance to Huanglongbing, or HLB, displayed by some Australian relatives of citrus.
There is no truly effective commercial treatment for HLB, also called citrus greening disease, which has destroyed orchards worldwide. The disease has already been detected in California, where 80 percent of the country's fresh citrus is grown. However, it has not yet been detected in a commercial grove.
To prevent that from happening, the National Institute of Food and Agriculture has awarded a UC Riverside-led research team $4.67 million. Chandrika Ramadugu, a UCR botanist leading the project, helped identify microcitrus varieties with natural resistance to HLB about eight years ago.
Cross section of a hybrid fruit bred for this project. (Chandrika Ramadugu/UCR)
“HLB is caused by bacteria, so many people are trying to control it with antimicrobial sprays,” Ramadugu said. “We want to incorporate resistance into the citrus trees themselves through breeding, to provide a more sustainable solution.”
Part of the challenge with this approach to solving the HLB problem is that it's possible to breed hybrids that are resistant to the disease but don't taste good, Ramadugu said. “Hence the need to generate a lot of hybrids and screen them for the ones that will be most ideal for the citrus industry.”
Microcitrus, such as the Australian finger lime, tends to have a sharper, more bitter taste than its relative citrus fruits, like oranges. The perfect cross will have just the right mix of genes to give it sweetness and HLB resistance.
Ramadugu's team includes collaborators from Texas A&M University, the University of Florida, Washington State University and the U.S. Department of Agriculture, as well as scientists from UC Riverside's Department of Botany and Plant Sciences.
Breeding project team members from UC Riverside's Department of Botany and Plant Sciences. (Chandrika Ramadugu/UCR)
Currently, the team is studying differences in the genetic makeup of the hybrids they've already bred. Analyzing the new plants' DNA will help the team see whether enough disease resistance has been bred into the fruit, but not so much that the flavor is compromised.
Another challenge with breeding is the time it takes for new citrus varieties to flower naturally, which can be several years. With the help of Sean Cutler, UCR professor of plant cell biology, the team is hoping to accelerate the time it takes for the hybrid plants to bear fruit in a greenhouse.
This way the hybrids can be analyzed for taste much sooner. Clones of the best hybrid plants will then be grown in Florida and Texas field trials.
UC Riverside scientists are using a variety of approaches to fight HLB. While some hope that altering soil and root bacteria will improve plants' immunity to the disease, others are trying to improve HLB resistance by tweaking citrus metabolism, or by using an antibacterial peptide to clear HLB from an infected plant.
The fruit produced through Ramadugu's method will appeal to many consumers because it will not have genes introduced into them by scientists. Breeding has been done for thousands of years to improve crops and is considered a more natural practice.
Additionally, Ramadugu says she's excited about her approach because it will ultimately produce a product useful for growers and consumers.
- Author: Ben Faber
from Dr. John Boland, Dr. Kellie Uyeda researchers, Dr. Jeff Crooks, advisor, Monica Almeida, cartography, Mayda Winter, project management
The Kuroshio Shot Hole Borer (KSHB) is a tiny beetle that invaded San Diego County in 2013. It was first seen in some avocado groves but then in 2015, it became very abundant in the native riparian forests in the Tijuana River Valley. It immediately caused extensive damage to those forests and as it is now also being found in many other sites in southern California, the authorities are extremely concerned that other sites are going to be impacted as badly as the Tijuana River Valley.
Luckily Dr. John Boland was studying the willow trees in the valley in 2015 and he immediately switched his focus to the KSHB's impact in the valley. Here we present a summary of the four main storylines coming out of his intensive five-year study of the beetles in the valley: the KSHB in the valley went through a 5-year boom-and-bust cycle; the KSHB severely damaged the native willow forests in the valley but the forests are now rapidly recovering; the research has uncovered two mysteries about the KSHB – one we think is solved and the other still needs to be solved; and the research has led to a prediction about KSHB's likely impact at other sites in southern California and several management recommendations.
When KSHB (Euwallacea kuroshio) attack a tree, the females drill into the trunk and create galleries of tunnels in the wood by pushing sawdust ‘tailings' out of the entrance hole. They inoculate the tunnel walls with a fungus (e.g., Fusarium sp.), and live in the tunnels eating the fungus and reproducing. Within a few weeks new females emerge, and start another gallery in either the natal tree or a new tree.
The beetles are tiny (~2 mm in length) and seldom seen, however if there are enough of them they can damage and even kill trees via their tunneling activities, which undermine the structure of the tree trunks.
The Tijuana River Valley and the riparian forest
The Tijuana River Valley in San Diego County, California, is a coastal floodplain of approximately 3,700 acres at the end of a 1,730 square mile watershed. The Tijuana River is an intermittent stream that typically flows strongly in winter and spring and is mostly dry in summer. For decades, the Tijuana River has been polluted with sewage and industrial waste as it flowed through the city of Tijuana, Mexico, and when it flows through the Tijuana River Valley it is one of the most polluted rivers in California.
The riparian forest that grows around this river is one of the largest in coastal southern California. The forest is dominated by just two tree species: the black willow (Salix gooddingii) and the arroyo willow (Salix lasiolepis). Both willow species are high on the list of KSHB's preferred hosts.
Annual surveys of infestation rates showed that the KSHB population went through a rapid outbreak and a rapid decline over a five-year period, with the infestation rates peaking in Fall 2016. The early increase in population occurred while the KSHB was attacking the willows in the Wet Forests and the later decrease in population occurred while the KSHB was attacking the willows in the Dry Forests.
The KSHB boom-and-bust is now complete. In fall 2019 it was difficult to find any trees infested with KSHB. While it lasted the KSHB's population explosion was very destructive: it has been estimated that the KSHB infested more than 375,000 willows and killed more than 122,000 willows in the valley.
This boom-and-bust cycle occurred naturally, with no management interventions to control the spread or severity of the outbreak.
Satellite image analyses conducted by Dr. Kellie Uyeda determined spatial and temporal patterns of canopy loss. The normalized difference vegetation index (NDVI), a metric of vegetation health, was calculated for each year from 2015 - 2019.
The remote sensing analyses support the results seen in the ground surveys. First, in the early years of the KSHB infestation, the most dramatic vegetation losses were observed in the Wet Forests and in later years the vegetation losses were observed in the Dry Forests, with lower levels of vegetation loss. Second, the KSHB's impact was greatest in 2016-17 and since then it has been tapering off.
Seedlings
After the KSHB had damaged the adult willows many willow seedlings recruited onto the sunny and moist river beds. Most of the willow seedlings were scattered within the forest, but three large stands of seedlings became established in three units.
A few old willows survived the KSHB invasion and remain as scattered Big Trees. It is likely that they will play an important role in the recovery of willows in the river valley.
Fortunately, the heavily-damaged Wet Forest units recovered considerably, and in some places the forests are almost back to their pre-KSHB condition. However, in other places they have failed to return because of the expansion of the invasive plant arundo, Arundo donax.
We think we know the answer to this mystery:
We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Why are the recovering willows not being re-attacked by the KSHB? The recovering willows in the Wet Forests are forming forests similar to what was present before the KSHB invasion, but the trees are not being substantially re-attacked by the KSHB. Why?
We don't know the answer but suggest these three possibilities: An ‘induced response' of the trees. It is possible that the infested willows have changed their chemistry as a result of the borer attack, and this has increased the resistance of the surviving trees to further borer attacks; overall forest structure. It is possible that the willows, though individually suitable, no longer present a suitable group target for the KSHB; and a disease or predator. It is possible that the KSHB population in the valley is now being kept low by a pathogen, parasite, parasitoid or predator. It will take further research to solve this mystery. But understanding it will provide essential information about the KSHB invasion in southern California and about shot hole borers in general.
Why was the KSHB's impact different in different parts of the valley? The distribution of KSHB within the Tijuana River Valley was not random; they infested and killed willows growing in or near the main channel significantly more than willows growing far from the water. On the wet site the mortality rate was high, and on the dry site the mortality rate was low. Black willow was the most abundant tree species in both sites. Why the difference?
We think we know the answer to this mystery: We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Management recommendations
Do not cut down and remove infested trees thinking that they are going to die. Willows can survive very heavy infestation rates. Remove Arundo in order to improve the riparian forests in the valley. Arundo is degrading the forests and needs to be removed for the willows to fully recover. Continue to plant willows in restoration sites. Use ‘natural restoration' methods wherever you can. When searching for KSHB in other parts of San Diego County search in nutrient-enriched areas, e.g., near storm drain outfalls. In urban forests do not over-fertilize or over-water trees. Nutrient-enriched and fast-growing trees are more vulnerable to KSHB infestation.
This research was funded by the Department of Navy on behalf of the Naval Base Coronado. Funds were managed by the Southwest Wetlands Interpretive Association.
The reports and some of the data analyses were done in collaboration with the Tijuana River National Estuarine Research Reserve.
And Read More: https://trnerr.org/kshb/