Questions for Deborah Samac

Learn more about my research In June 2008, Deborah Samac answered visitors questions about plant pathology.

Your Comments, Thoughts, Questions, Ideas

Joe's picture
Joe says:

What inspired you to pursue a career in plant pathology?

posted on Thu, 06/12/2008 - 11:47am
Deborah Samac's picture
Deborah Samac says:

I have always enjoyed growing plants. My mother is a terrific gardener and passed on her love of gardening to me. In college I did research on the desert shrub called jojoba and found that I really enjoyed discovering new knowledge. My first job once I graduated was working in a plant biotechnology lab with people trying to understand how plant viruses interact with their plant hosts. I found the communication between plant pathogens and plants to be fascinating. That fascination has stayed with me my entire career. So, my job combines the three things I enjoy the most: working with plants, discovering things no one has known before, and understanding how plants and microbes communicate and interact.

posted on Tue, 06/17/2008 - 3:52pm
JGordon's picture
JGordon says:

You're making alfalfa more resistant to certain diseases by inserting new genes into the plant--where do those genes come from? What other kinds of traits (besides disease resistance) can be inserted into crops?

posted on Fri, 06/20/2008 - 3:28pm
Deborah Samac's picture
Deborah Samac says:

One of the really interesting phenomena in biology is that DNA is a universal code. For the most part, an alfalfa plant can “understand” the DNA code of a gene from any other organism and produce the correct protein from that gene. So, we have used genes from bacteria, fungi and other plants in alfalfa. Using these genes we have produced alfalfa plants that can make a biodegradable plastic that can be used to make plastic bottles, bags and medical devices. We have produced alfalfa plants that can take up and degrade pollutants in soil and water. We have produced alfalfa that can tolerate acidic soils. Other groups have made alfalfa plants that are easier for animals to digest and that will be less costly for producing renewable energy. The limitation now is that we can only transfer two or three genes at a time into a plant. A current trend is to identify and transfer regulatory genes that turn on whole metabolic pathways. In the future, a small chromosome may be transferred allowing many genes to be transferred at once.

posted on Tue, 07/01/2008 - 8:36pm
Anonymous's picture
Anonymous says:

What causes dutch elm disease? You don't hear as much about it these days - is it over?

posted on Sun, 06/22/2008 - 10:08pm
Deborah Samac's picture
Deborah Samac says:

Dutch elm disease is caused by a fungus called Ophiostoma novo-ulmi. The disease is called Dutch elm disease because the earliest descriptions of the disease came from the Netherlands. However, it appears that the fungus originated in Asia and was moved by people to Europe and North America. It is a very destructive disease. The disease has killed more than 40 million elms and there have been enormous costs for removing and replacing diseased trees.

The disease is the result of an unusual partnership between the fungus and an insect. Although the fungus causes the disease, elm bark beetles are indispensable for moving the fungus from a sick tree to healthy trees. Consequently, when the elm bark beetle flourishes, then Dutch elm disease flourishes. The disease is still around and plaguing city trees. In 2005-2006 we had weather in the Twin Cities that favored elm bark beetle reproduction. This was followed by a resurgence of Dutch elm disease and the rapid loss of old trees once thought to have escaped the epidemics. Because the beetles are so efficient at moving the fungus, it is important to remove diseased trees as soon as possible to limit spread to neighboring trees. Elm trees with resistance to Dutch elm disease have been developed and will help to bring back this lovely shade tree to city streets.

posted on Mon, 06/30/2008 - 7:25pm
Anonymous's picture
Anonymous says:

What is the biggest bug problem for Minnesota plants today? And, is that bug a native Minnesota region bug or an invasive species?

posted on Sun, 06/22/2008 - 10:10pm
Deborah Samac's picture
Deborah Samac says:

What you consider the worst bug depends on who you are. For a lot of people the worst bug is probably the one that is eating the plant that they care about the most! In my work I specialize on the micro-organisms that feed on plants. I asked a friend who is an entomologist (a scientist who studies insects) about what he considers the worst insect. Here is his answer:

That is quite a question! There is not a single pest that tops the list year after year. New pests are introduced and old pests find new ways to cause problems.

Soybeans are a major crop in Minnesota. The soybean aphid, a native of eastern Asia, has been in the U.S. since 2000, and possibly as early as 1995. It has done a lot of damage and caused major losses in agriculture.

For Minnesota forests and urban trees we need to pay attention to the emerald ash borer. This introduced species in not known to be in Minnesota, but it is in northern Illinois and has killed more than 30 million trees since the early 1990s. University of Minnesota Extension recently held an emerald ash borer awareness week. Minnesotans are asked to not transport firewood within the State and not purchase firewood outside the State. This is one case where our behavior can make a huge difference in avoiding a major problem.

As an example of how old pests can adapt and resurge, corn rootworms have recently found two ways to circumvent crop rotation. The northern corn rootworm now has eggs that can persist in soil for two or more years and hatch after the field is rotated back to corn. Subpopulations of the western corn rootworm, a closely related species, now lay eggs in soybeans. These eggs hatch the following year when corn is planted in the field. Corn rootworm species are the most serious pests of corn in the Midwest, and rootworm control just got more complicated and expensive. Things change over time; new pests arrive and old pests adapt. It is a fluid situation and source of great fascination.

posted on Mon, 06/30/2008 - 7:45pm
matt's picture
matt says:

Can people catch diseases from plants?

posted on Tue, 06/24/2008 - 3:25pm
Deborah Samac's picture
Deborah Samac says:

No, you cannot get a disease from a sick plant. People do not get the same diseases that plants get. However, some people may be allergic to the spores produced by some plant pathogenic fungi.

posted on Mon, 06/30/2008 - 7:31pm
Anonymous's picture
Anonymous says:

What is your favorite plant to learn about?And why?

posted on Tue, 06/24/2008 - 7:48pm
Deborah Samac's picture
Deborah Samac says:

I like all kinds of plants so it is hard to choose a favorite! In particular I find the diversity among plants and what they do to be amazing. Professionally, I have enjoyed learning more about a small plant called barrel medic. It is closely related to alfalfa, the crop plant that I work on. Several years ago barrel medic was chosen to be a model for plants in the bean and pea family. We need models because crop plants have been selected by people for hundreds, sometimes thousands of years, and so they are very complicated at the genetic level. Models can “stand in” for the crops and are much more simple to study. The barrel medic plant is one of the “lab rats” of the plant world. We already have almost all of the DNA sequence from this plant and have a catalog of all of its genes. I am using barrel medic to identify genes for disease resistance that can be used to increase disease resistance in crop plants.

posted on Tue, 07/01/2008 - 8:37pm
From the Museum Floor's picture

How can you tell the difference between male and female plants?

posted on Mon, 06/30/2008 - 12:19pm
Deborah Samac's picture
Deborah Samac says:

The way to tell the sex of a plant is to look closely at the flowers. Many plants have what are called perfect flowers, that is, they have both male and female parts. The male parts are the anthers that have the pollen (usually yellow colored). The female parts can be harder to see. The stigma is often the easier part to see, usually in the center of the flower, and receives the pollen. It is held up on a column-like structure called a style. The ovary, where the seed is produced, is below the style). Take a look at a lily flower and you will be able to see the anthers and the stigma pretty easily. Some plants have separate male and female flowers on the same plant. On a corn plant the tassels at the top have the anthers and the ears are the female parts. A few plant species have male and female flowers on separate plants. One example of this situation is the ginko tree.

posted on Tue, 07/01/2008 - 3:51pm
From the Museum Floor's picture

What you are doing is cool, but why alfalfa? What made you pick that plant?

posted on Mon, 06/30/2008 - 12:20pm
Deborah Samac's picture
Deborah Samac says:

Although most people don’t realize this, alfalfa is the third most commonly grown crop plant in the US. The first two are corn and soybeans. The main use of alfalfa is as an animal feed, mostly for dairy and beef cattle because it is a highly nutritional feed for animals. Alfalfa also plays many other important roles in agricultural systems. One of its important attributes is that it can host beneficial bacteria in its roots. The plant and bacteria join forces to covert nitrogen gas from the air into amino acids, which are the building blocks of proteins. This process is called nitrogen fixation. Because of nitrogen fixation, alfalfa does not need nitrogen fertilizer. When corn is grown after an alfalfa crop, there is enough nitrogen in the soil from the alfalfa that the corn doesn’t need fertilizer. Alfalfa is a perennial plant, meaning it regrows year after year. It also has a very deep root system. Because it grows early in the spring before other crops and has such a vast root system, it helps prevent soil erosion and captures nutrients that move through the soil in the early spring. Alfalfa also produces a lot of biomass. Part of our work is to develop alfalfa for use as a renewable energy source. So, we are interested in alfalfa because it is a major crop that has many uses, and because growing alfalfa provides many benefits to the environment.

posted on Tue, 07/01/2008 - 4:17pm
From the Museum Floor's picture

My shrub bush has a white "mold" on it, what causes this and what can I do about it? Others I have don't have this - just one. It does not seem to be bothering or killing the plant.

posted on Mon, 06/30/2008 - 12:21pm
Deborah Samac's picture
Deborah Samac says:

Diagnosing plant diseases, just like diagnosing human and animal diseases, can be tricky. I would need to know what kind of shrub you have, where the white mold is located, and more about what the mold looks like. Many plants get a fairly harmless disease called powdery mildew that looks like white powder on the leaves. However, this usually occurs in the fall, not in the spring. If you are really curious about what is going on with your plant, I suggest that you take a sample in to a garden center. They will probably be able to narrow down what is on your plant. If it does not seem to be causing a problem or spreading to other plants, I suggest that you just letting it be, but keep an eye on it to see if it changes over time.

posted on Tue, 07/01/2008 - 4:01pm
Sarah's picture
Sarah says:

How exactly do plants become sick? How do you treat them if they receive infections?

posted on Tue, 07/01/2008 - 2:16pm
Deborah Samac's picture
Deborah Samac says:

Plant pathogens can be separated into two general groups based on how they infect plants. One group is called the necrotrophs. “Necro” means dead and “troph” means nourishment so a necrotroph feeds off of dead plant material. These pathogens usually make toxins that kill plant cells or enzymes to break open plant cells. Then they use the material in the dead areas to grow and reproduce. Sometimes the cell death is limited to a small spot. You may see leaf spots if you look at plants in a garden on in natural settings like a wood or prairie. If the environmental conditions are right and the plant lacks defenses against the pathogen, the spot can spread to kill an entire leaf and eventually kill the whole plant. The other group of pathogens are called biotrophs. As you probably guessed, these pathogens use living plants for nourishment. Some live on the surface of plants. In the autumn you can often see biotrophic pathogens on plants as a white powder on leaves. This is likely a plant disease called powdery mildew. Other biotrophs can live inside of plants. Many of these live in the water and food conducting vessels. Growth of pathogens in these vessels results in wilting of plants because the vessels get clogged or broken and cannot function. The biotrophs weaken plants by taking nutrients from the plants to support growth and reproduction of the pathogens. The infected plant may die or may be too weak to produce many flowers or fruit if it is infected early in the growing season.
The appropriate treatment depends on what pathogen is causing the disease, what plant is infected, where it is growing (the local environment) and how valuable the plant is. Whole books are written on this topic, but I will try to give you short answer! Most of a plant pathologist’s efforts go into keeping plants healthy because it can be difficult to cure a plant of a disease. To get disease, three conditions must be met; there must be a virulent pathogen, a susceptible plant, and a conducive environment. There also needs to be time for the pathogen to infect and cause disease. We work at preventing one or more of those conditions. However, if a plant does get sick and if the disease has not progressed too far, certain chemicals can be applied to kill or slow down the pathogen. If the pathogen is just on one part of the plant, the infected area can be removed to keep if from spreading to the rest of the plant. Often the sick plant or plants are removed to keep the disease from spreading to neighboring plants.

posted on Mon, 07/07/2008 - 4:59pm
Cara's picture
Cara says:

Is it important to eradicate purple loosestrife, and if so, how?

Thanks

posted on Wed, 07/02/2008 - 5:26pm
Deborah Samac's picture
Deborah Samac says:

Purple loosestrife is an exotic invasive plant. Settlers in North America introduced it from Europe. It spreads rapidly in moist and wet environments. It makes very thick stands that are not good for habitat for animals and that also prevent growth of native plants. This web site (http://www.seagrant.umn.edu/ais/purpleloosestrife_info) has lots of information on how to remove purple loosestrife depending on how large the area is and how dense the plants are. One big advance in the last few years is the use of insects, or natural predators of the plant, to help reduce populations of purple loosestrife. Such biological controls have to be used carefully to make sure that introducing another organism does not cause additional problems, but they can be very effective control methods. The website also has good information about biological controls of purple loosestrife.

posted on Mon, 07/07/2008 - 4:36pm
Anonymous's picture
Anonymous says:

What is the most poisonous plant to humans?-

posted on Mon, 07/07/2008 - 3:10pm
Deborah Samac's picture
Deborah Samac says:

Many plants produce compounds that can be toxic to people and animals. To me the interesting question is why do plants use energy to make these toxins? Some of the toxic compounds are made during normal growth and development. For example, there are proteins in many seeds that inhibit digestive enzymes from functioning. These likely keep animals and insects from feeding on the seeds. Humans figured out that cooking the seeds inactivates these proteins and makes the seeds fit to eat. When pathogens and insects attack plants, the plants can make compounds to slow down or stop the invader. Some of these compounds are toxic to people and animals. In fact, the plant I work on (alfalfa) can be found on lists of toxic plants because of the compounds it makes when attacked. However, animals eat millions of tons of alfalfa each year without a problem, mostly because we have developed alfalfa that is highly resistant to diseases and the plants don’t have to make their toxic defense compounds. Sadly, I think the most toxic plant to people is the tobacco plant. The plant naturally makes nicotine and many other cancer-causing compounds in its leaves. Smoking tobacco leads to 123,386 lung cancer deaths per year, far more than any other type of cancer.

posted on Tue, 07/15/2008 - 10:05am
Anonymous's picture
Anonymous says:

What is the longist living plant on Earth.

posted on Tue, 07/08/2008 - 3:10pm
Deborah Samac's picture
Deborah Samac says:

There are several ways to answer your question. There are some plants that grow as a colony of identical individuals known as clones. The colony can live for many, many years although an individual plant may have a fairly short life span. For example, a colony of aspen trees has been estimated to 80,000 or even 1 million years old! There are also plants that have lived on the planet for millions of years relatively unchanged over time. However, the individuals may have a fairly short life. One example of such plants are the cycads, which were around at the same time as the dinosaurs. You were probably wondering what is the oldest individual plant. That honor, as far as we know, goes to a bristle cone pine tree in California, which has been dated at 4,838 years. To me the interesting question is what makes a plant long lived? We still don’t have good answers to this. In my work, we are comparing two plants that are very alike at the DNA level, alfalfa and barrel medic. Alfalfa is a perennial plant and grows new foliage every spring from roots that survive the winter. Barrel medic is an annual plant. In other words it grows from a seed, flowers, produces new seed and dies within several months. Even though the plants share most of the same genes, we are discovering that they differ in when and where they turn genes on. Eventually we hope to discover what makes one plant a perennial and the other an annual. It may be beneficial to farmers, consumers and the environment to have more perennial crop plants.

posted on Tue, 07/15/2008 - 10:36am
Anonymous's picture
Anonymous says:

Are box elder bugs harmful?

posted on Fri, 07/11/2008 - 10:51pm
Deborah Samac's picture
Deborah Samac says:

Boxelder bugs are common insects in Minnesota. They may become more noticeable in the fall when they look for safe places to spend the winter. Sometimes they are attracted to houses for a wintering site and can be a nuisance if they invade your house in large numbers. In summer they feed on leaves of boxelder, maple and ash trees but do not do significant damage to the trees. There is a great web site with lots of information on these critters at:
http://www.extension.umn.edu/distribution/horticulture/DG0998.html

posted on Tue, 07/15/2008 - 10:44am
Anonymous's picture
Anonymous says:

What is feverfew? My mom says she knows it is a plant but does not know anything else about it. She says it was in her crossword puzzle.

posted on Fri, 07/11/2008 - 10:52pm
Deborah Samac's picture
Deborah Samac says:

Feverfew is a plant in the sunflower family. It looks a lot like a daisy with a yellow center and white petals. It is native to Europe and can be found in many herb gardens in the North America. It has been used as a folk remedy for a number of problems, including reducing fever. The plant is also the source for pyrethrum, which is used as an insecticide. Some people are sensitive to such compounds so the plants and pyrethrum should be handled carefully.

posted on Tue, 07/15/2008 - 10:59am
JGordon's picture
JGordon says:

Do inserted genes stay in alfalfa generation after generation? Or is there a certain point at which seeds will just produce "normal" alfalfa? And—if they stick around—could inserted genes play a role in the future evolution of the plant?

posted on Mon, 07/14/2008 - 4:31pm
Deborah Samac's picture
Deborah Samac says:

In most cases the inserted gene or genes stay in the plant’s chromosomes from one generation to the next. But in some cases they are deleted or changed by the plant. Every time a cell divides, there is some amount of genetic rearrangement or recombination. It appears that plant cells can detect the newly inserted genes as “foreign” and delete them during this recombination process. Plants also can modify DNA so that the inserted genes are no longer active and seem to be lost since the trait they give to the plant is not longer exhibited. All genetically modified plants go through years of testing to see if the inserted DNA is stable in the plant. One of the exciting results from plant genome sequencing projects in which all of the genes in a plant are identified, is that plants appear to have been acquiring genes from diverse organisms for millions of years. The DNA stays around if it gives the plant an advantage over plants that lack the DNA or if the new DNA does not result in a disadvantage to the plant, that is, it doesn’t “cost” anything. Most of our crop plants are “domesticated” and would have great difficulty in surviving in the wild with out human help. Also, most of our crop plants do not have relatives growing nearby that they are closely related to and could reproduce with. So, it is not very likely that the genes inserted by people into crop plants will play a role in future evolution of the plant species.

posted on Thu, 08/07/2008 - 11:43am
Anonymous's picture
Anonymous says:

Is the University of Minnesota a major place where plant pathology work is being done? What other research is happening there in this field?

posted on Thu, 07/31/2008 - 10:12am
Deborah Samac's picture
Deborah Samac says:

The Plant Pathology Department and the University of Minnesota was the first university department dedicated to the study of plant diseases in the United States. It was established in 1907. It is among the top-rated departments of Plant Pathology in the country. One of the main reasons that the Department was created was to combat wheat stem rust. At that time wheat was HUGELY important to Minnesota and the Dakotas, and Minneapolis was the center of flour milling in the country. The disease of wheat called wheat stem rust was wiping out the wheat crop across the region. The scientists at the time identified disease resistant wheat and began creating disease resistant varieties. They also recognized that the barberry plant was another plant infected by the rust fungus. They found that the fungus reproduces sexually on barberry and that this results in more variation in the fungus. They showed that by removing barberry plants, the wheat plants had less disease and the resistant varieties retained resistance much longer. Research on wheat rusts continues at the University of Minnesota today because the fungus continues to change and adapt. In 1999, a wheat stem rust variant was found in Africa that causes disease on most of the wheat varieties currently grown. Scientists around the world, including those at the University of Minnesota, have mobilized to develop new wheat varieties that are resistant to this new strain of the stem rust fungus.

The research on wheat diseases is just one of many current research projects on plant diseases at the University. We are also investigating a threat to soybeans called Asian soybean rust. This disease is common in Brazil and has recently moved into the southern US. We are studying how the fungus moves, what conditions are needed for disease to occur, and how to combat the disease. We are also monitoring for the rust every summer to be able to alert soybean farmers to a potential threat. We also have scientists who study the genes in plant pathogens to discover the ones that enable them to cause disease. Other scientists study the genes in plants that enable them to resist diseases. In both of these areas we have just begun to understand these complex processes. Disease resistance in plants will likely turn out to be far more complicated than disease resistance in humans and animals at the cellular level. We also have scientists who study microbes associated with plants that influence plant health, sometimes by promoting plant growth, sometimes by inhibiting pathogen growth, and sometimes by means that we have yet to discover! Recently, scientists have recognized that there are LOTS of microorganisms on the surfaces and inside plants, but we know little about how they influence plant growth and plant health. Our research is not limited to crop plants but includes forest trees, vegetables, ornamental plants, and native plants. Our research is not limited to Minnesota. Scientists in the Department do research in many parts of the world including the artic and Antarctica. To read more about our past and current research please see: http://plpa.cfans.umn.edu

posted on Thu, 08/07/2008 - 11:47am
Anonymous's picture
Anonymous says:

My local garden center had preying mantises that I could buy (as eggs) to release into my back yard as a form of pest management. Why isn't this considered introducing a non-native species?

posted on Thu, 07/31/2008 - 10:13am
Deborah Samac's picture
Deborah Samac says:

Most likely, the egg cases of praying mantis available in your garden center are from the European or Chinese mantis. You are correct, releasing them in your yard would be release of a non-native species. Both of these insects have been used for insect control in the US for many years. They are considered to be beneficial and have not appeared to threaten native praying mantis species. In other places in the world such as New Zealand, release of a non-native praying mantis species has had negative consequences on native mantis species.

posted on Thu, 08/07/2008 - 11:48am
Gianna's picture
Gianna says:

I cut down one of my three pear trees due to fire blight two years ago. Now one of it's shoots seem to be growing quite well in it's place. Will this plant suffer from fire blight as well because the parent tree did?
Thank you.
Gianna

posted on Wed, 08/06/2008 - 2:06pm
Deborah Samac's picture
Deborah Samac says:

The fire blight bacterium can infect all parts of a pear or apple tree. It can move into the trunk and roots from infected branches. If you haven’t seen any symptoms yet, you may have removed all of the bacteria when you cut down the first tree. Pears are very susceptible to fire blight, even more susceptible than apples. The new shoot could still get infected from bacteria coming from nearby infected trees. Bees and other insects move the bacteria in early spring. Later in the growing season bacteria can spread by wind-blown rain from nearby infected trees. Very lush new growth is the most susceptible to infection. So, it is important to not over-fertilize the tree during the summer and to remove any infected nearby trees in order to try to keep your tree healthy.

posted on Fri, 08/08/2008 - 1:43pm
Anonymous's picture
Anonymous says:

Is it true that flapping cottonwood leaves cool the air around them due to the water evaporating from them? Do any other plants act as air conditioners?

posted on Tue, 08/19/2008 - 1:37pm
Deborah Samac's picture
Deborah Samac says:

There are many benefits of having trees in the city landscape. It is true that trees cool the air by evaporating water from their leaves. This occurs in all plants, not just cottonwood trees. Also, the leaves can be still, they don't have to be moving for evaporation to occur. However, cottonwoods have a high rate of evaporating water from leaves. So, they may be better air conditioners than trees that have a lower rate of evaporation. Trees also cool the ground and buildings by providing shade. Additional benefits to having trees in the city are that they help reduce smog, sequester carbon and give off oxygen. All good reasons to plant more trees!

posted on Wed, 08/20/2008 - 3:46pm
Anonymous's picture
Anonymous says:

What is next for your research?

posted on Tue, 08/19/2008 - 1:38pm
Deborah Samac's picture
Deborah Samac says:

This is an exciting time to be a biologist, especially a plant biologist! One reason is that people are more conscious of the need for providing healthy plants for food and energy while conserving soil and water resources. Part of our research is to develop alfalfa varieties that have multiple uses as animal feed, for providing renewable energy, for cleaning up water and soil, and as a raw material for industry. Many new, high tech tools are now available for understanding how plants and microbes work and how they interact. We are rapidly deciphering the gene sequences for crop plants and their associated microorganisms. This allows us to identify what genes are active during different times in plant development or when the plant is responding to a pathogen. We used to be able to measure only one gene at a time. Now we can measure activity of thousands of genes at the same time. This lets us see the plant and the pathogen as a whole system, not just in isolated parts. I am interested in identifying the master switches in plants that get triggered when it is attacked by a pathogen and then tracing the different genes that get turned on as a result of the master switch being activated. By activating some of these master switches we can enhance disease resistance and other desired characteristics in plants.

posted on Wed, 08/20/2008 - 4:03pm