Unlike sugarbeet growers, who harvest the fruits of their labors every year, those who conduct basic research on this crop may not witness the commercial payoff from their work for a decade, two decades — or even longer. While we all need a certain amount of patience and persistence in our jobs, no one relies on such traits more than public scientists like Larry Campbell, Karen Fugate and Melvin Bolton.
Using Molecular Technology to Fight Disease
Sugarbeets contend with a number of diseases, including several of huge economic importance. One of Fargo ARS plant pathologist Melvin Bolton’s primary goals is to gain a better understanding of how the various disease pathogens are able to “manipulate” the sugarbeet plant. Such information then can be used “to hopefully develop lines with improved disease resistance, based on what we know about what the pathogens are doing,” he observes.
That objective is not new, of course. Plant pathologists around the globe have, for decades, sought to better understand such pathogens in order to develop effective control measures (fungicides, host plant resistance, cultural practices). Today, however, plant pathologists and geneticists are employing a wonderful new weapon in their disease-fighting arsenal: molecular technology. Initially quite expensive, this weapon has become increasingly affordable in recent years.
“Even 10 years ago, gene sequencing was still pretty expensive,” Bolton says. “But the cost to do the types of things we’re interested in doing has dropped dramatically (due to competition among providers). A procedure known as next-generation sequencing allows Bolton and fellow scientists to sequence (map) the entire genomes of important sugarbeet pathogens like Cercospora beticola. Doing so provides them with a much better understanding of these pathogens’ biology — which is essential when developing the tools (host plant resistance, new fungicides, etc.) for controlling the diseases.
A key component of Bolton’s molecular technology program is the identification of important proteins or toxins produced by pathogens during the course of infection. These molecules, commonly known as “effectors,” are secreted during fungus colonization. In a process quite similar to how a human body’s immune system operates, the sugarbeet’s host resistance gene “will recognize that effector, turn on the defense response — and kill the pathogen,” Bolton explains. “So if we can find an effector that’s important to the pathogen and is potentially recognized by a host resistance gene, that can be a way to deploy resistance into commercial lines.”
One of the more-exciting developments of late is the use of a molecular technology called “quantitative PCR” to identify fungicide-resistant strains very quickly. A prime example is Cercospora resistance to certain strobilurin fungicides, which has shown up in Michigan and sugarbeet areas of Italy. In the past, North Dakota State University plant pathologist and collaborator Gary Secor, whose group tests for such resistance, would have to take submitted leaf samples, isolate the fungus from the samples, grow it via sterile techniques in the laboratory — and then mix the fungicide with the resulting medium in petri dishes to determine whether the fungus was resistant. It was a process that could take up to several weeks to complete.
“Now, we’ll get a leaf sample, take a paper punch of a leaf spot — and, because we know there’s a mutation associated with resistance, within two hours we can tell you whether that fungus is resistant to the fungicide or still susceptible,” Bolton advises. Such a vastly accelerated process means that they can advise a grower on a very timely basis whether it’s worth spraying that particular fungicide. “Before, if you had a high-disease-pressure summer, you might not get that information fast enough to be of use,” Bolton points out. “Now we can get it to you really fast — and cheaper than it was before.” The 2012 growing season is the first in which this new technology is being put to the test by sugar company agriculturists and growers.
Bolton, Secor and NDSU/UM sugarbeet specialist Mohamed Khan also have collaborated in using molecular technology to help identify a new species of Fusarium that is causing localized serious damage in the southern Red River Valley. He believes this strain is much more aggressive than the more-familiar Fusarium oxysporum. The new species causes severe early season yellowing and scorching of leaves, vascular discoloration of the taproot, and early plant death. “It may warrant new resistance breeding strategies if the pathogen becomes more widespread,” Bolton notes.
Breeding for Root Maggot Resistance & Lower Impurities
Breeding for resistance to the sugarbeet root maggot (SBRM) has been a core focus of Campbell’s research throughout his tenure with the Fargo ARS team. The root maggot is not a pest of European sugarbeets; nor is it present in all North American beet regions. So no breeding for SBRM resistance is being conducted elsewhere. While this insect historically has plagued sugarbeets in several parts of the Red River Valley, its population levels and economic threat currently are greatest in the Valley’s northern reaches — especially Pembina, Walsh and Grand Forks counties of North Dakota.
The Fargo SBRM resistance breeding program was initiated by Campbell back in 1983 with encouragement and assistance from North Dakota State University entomologist Albin “Andy” Anderson. Three root maggot-resistant lines have been released to date. The latest (F1024), released in 2009, combines a high level of root maggot resistance with moderate resistance to Cercospora leafspot. As with all germplasm developed by USDA breeders, these lines are available to interested commercial sugarbeet breeders for evaluation and potential use in their own hybrid development programs.
No one has been able to develop a successful system for rearing sugarbeet root maggots in the laboratory or greenhouse, so Campbell and his group must conduct their research and evaluations out in the field. “All selection for resistance and root maggot damage evaluations rely on natural infestations in the northern Red River Valley, at sites near St. Thomas, N.D.,” he notes.
The availability of a few registered insecticides for SBRM control has been critical for sugarbeet growers in those areas where the root maggot is an economic problem — especially in lieu of SBRM-resistant hybrids. Should some of those insecticides lose their efficacy, however — or should some be withdrawn from the market for whatever reason — having resistant hybrids would take on vital importance, Campbell points out. “Root maggot-resistant hybrids would be similar to having hybrids with resistance to Cercospora or Rhizoctonia: you may not completely eliminate the maggot from your fields; but you would reduce the damage considerably.”
While it consumes the majority of his time, root maggot resistance is not Campbell’s only area of research. He also works to develop breeding lines with lowered impurities (sodium, potassium and amino-nitrogen). The lower the levels of these impurities, of course, the higher the sugar extraction levels in the factory.
“The objective of this research is to provide insight into the extent each of these impurities can be reduced without having negative effects on root yield and sucrose concentration,” Campbell explains. Corollary evaluation examines the interaction among the individual impurity components that may either hinder or facilitate processing quality enhancement. Three germplasm lines with reduced sodium, potassium and amino-nitrogen concentrations, respectively, were released by Campbell’s program in 2011.
Storage Research: Maximizing Sucrose Retention
When Karen Fugate first joined the Fargo ARS sugarbeet group 14 years ago, her main charge was to study ways to increase the accumulation of sugar within the sugarbeet plant. That was all well and good. But then it dawned upon her and others that it was equally important to focus on retaining as much of the sugar that was already present at season’s end. In other words, what could be done to minimize the loss of sugar during the storage period between harvest and processing?
As such, Fugate’s research encompasses four major objectives: (1) determine the metabolic factors that affect sucrose accumulation and root yield during production; (2) determine the metabolic factors that affect sucrose loss during storage; (3) determine the impact of production diseases on root storage properties; and (4) investigate the usefulness of inducing the sugarbeet plant’s native defense mechanisms to reduce storage losses.
Those first two objectives have largely revolved around (a) the role of sucrose-degrading enzymes in the sugarbeet plant root and (b) those enzymes’ impact on sucrose content, root yield and sucrose loss during storage. Since respiration is the single most important cause of postharvest sucrose loss, Fugate also has conducted research aimed at better understanding what factors within the beet root actually regulate storage respiration rates. That information “could lead to the development of metabolic or genetic markers to screen germplasm for improved storage characteristics,” she says.
When present in stored beet roots, diseases like Aphanomyces root rot, Fusarium yellows and Rhizomania are major contributors to quality deterioration and sucrose losses — sometimes of a very large economic magnitude. Fugate’s research (Objective #3), conducted jointly with Larry Campbell and, most recently in collaboration with Dr. Carol Windels of the University of Minnesota-Crookston, has quantified the detrimental effects on storage properties caused by roots infected with various levels of these diseases.
This information is proving useful to sugar company agronomists and storage pile managers in deciding how to manage beet piles — including whether to keep certain beets out of the piles altogether.
Objective #4 is more long-term in nature. It focuses on determining the ability of certain sugarbeet plant hormones (i.e., jasmonic acid and salicylic acid) to reduce storage losses. “Initial research with jasmonic acid acid demonstrated the ability of this compound to protect roots against Botrytis, Penicillium and Phoma,” Fugate reports.
‘Each Step Is Exciting’
All three Fargo ARS sugarbeet scientists agree that while the fruits of their labors are distinctly futuristic — and often exceedingly so — they have little problem remaining committed to their mission. Success typically comes in increments, not in dramatic breakthroughs. But the motivation persists.
“We make these little steps,” Melvin Bolton summarizes. “But each step is exciting — even though it may be small. There is so much to learn on so many different levels. There are plenty of things to keep us motivated and excited.”
The ever-dynamic relationship between plants and pathogens provides a clear window into why pathologists like Bolton will never run out of challenges. “One of the issues in plant pathology is that we may find a nice resistance gene that provides [protection from] an important pathogen — but these pathogens can mutate and overcome that resistance,” he illustrates. “So it’s a constant battle. The pathogen will win for awhile; then the host plant will win for awhile.”
Mother Nature doesn’t give up her secrets easily, Karen Fugate concurs — and that is why researchers like her seldom are bored. “What gets me excited is the process, seeing progress,” she affirms. “Sometimes you do things that don’t work out very well, which is disappointing. But that usually opens up new doors, and you go in directions you previously didn’t expect to go.”
For Larry Campbell, knowing he and his colleagues played a key role in the development of today’s commercial sugarbeet varieties and those yet to come is inherently gratifying. “With a lot of what’s out there — Cercospora resistance, for example — the seed companies produce the final product. But if you look at the sources of resistance, you’ll find they often [were developed] by USDA programs,” he states. “They’re putting together the final product; we’re supplying germplasm that [helps lay the foundation]. It’s a good partnership.” — Don Lilleboe