A good infection
Endophytic fungi offer several advantages to grasses. However, advances in this field are hard to come by.
One of the more intriguing discoveries in the history of turfgrass science is the endophyte. As defined by Webster's dictionary, an endophyte is a "plant living within another plant." In the case of grasses, the endophyte is actually a fungus that lives, grows and thrives inside a host plant. The endophyte and the grass plant form a mutually beneficial relationship; the plant feeds and "houses" the endophyte while the endophyte helps the plant survive insects, heat and drought. Many different types of endophytes are widespread in grasses, but most have not been thoroughly studied. For the purposes of this article, we will focus on the endophytes found in cool-season grasses, as these are the best understood and the most useful to turf managers.
History and discovery Scientists discovered endophytes during a search for answers to a serious problem unrelated to turf. In the 1940s, people began to recognize that cattle, sheep and horses, grazing in tall fescue pastures in the United States and perennial ryegrass pastures in New Zealand, would occasionally develop weight-gain problems. Often, the animal suffered from chronic necrosis and a general unhealthiness. These conditions could be so severe that cattle became lame and even lost their tails or hooves. Horses could experience stillborn foals and a lack of milk production.
In 1976, researchers in Georgia, Dr. Joe Robbins and Dr. Charles Bacon, compared the performance differences of cattle in separate, but adjacent pastures. Plants in the pasture where animal gains were lowest contained a fungal endophyte. The endophyte was found to severely affect animal weight gain and overall health. It produced (or it caused the plant to produce) many toxic compounds. Therefore, the presence of endophytes was detrimental, and forage grass breeders started to work on developing endophyte-free varieties.
As researchers realized the negative effect endophytes had on animals and worked to remove them from pastures and forage grasses, they also discovered endophyte-free pastures had less persistence and would not maintain a good sward. Researchers in New Zealand removed the endophyte from perennial ryegrass to improve sheep growth and found the grass lost resistance to a significant insect pest, the Argentine stem weevil. This discovery led researchers to look more closely at the benefits that endophytes might provide the plant.
In the early 1980s, Dr. C. Reed Funk at Rutgers University started investigating the potential insect resistance of endophyte-infected perennial ryegrass plants. He found outstanding resistance to insects that feed on leaves and stems.
The highest concentration of endophyte occurred in the crown, stems and leaves, while low amounts existed in the roots. This made sense because there was little resistance to insects that feed on roots. Further, Funk discovered that endophytes could transfer from one plant to another when using conventional plant breeding techniques. Hence, endophyte-infected turfgrasses were born.
How endophytes live and reproduce Endophytes form mycelia (growth structures) that grow between the cells of a plant, mainly in the leaf sheaths and reproductive structures. As seed production initiates, the endophyte grows upward in the plant. When the seed forms, the endophyte infects the outer layers of the seed. This is how the endophyte transfers from plants in a seed production field to seed that you buy for turfgrass plantings. When the seed germinates and grows, the endophyte infects the new plant and moves into the growth areas of the plant.
Because endophytes are living organisms, we must properly store the seed so that the fungi are not killed. Also, there is no quick, easy method to determine endophyte viability in seed. High temperatures and high humidity conditions, like those experienced during summers in the mid-Atlantic area, will kill endophyte in seed, but not the seed itself. Therefore, if your seed germinates, it does not necessarily indicate that the fungus is also still alive.
Some seed-testing laboratories can test for percentage live endophyte. However, this test may take up to six or eight weeks. Therefore, always purchase new seed (seed harvested in that year) or investigate the storage conditions. Also, if you store seed for a period longer than three months, keep it in a cool, dry place.
How endophytes work Endophyte-infected grasses show excellent resistance to damage from insects such as sod webworms, chinch bugs and armyworms. These insects feed mainly on grass blades, leaf sheaths and crowns, where endophyte concentration is the highest. Researchers have identified many compounds in endophyte-enhanced grasses that they suspect give the plant resistance to insects and tolerance to various environmental stresses. Of these compounds, alkaloids (nitrogen-containing compounds that cause responses at low concentrations in living organisms) are the subject of most studies. Several alkaloids are toxic to animals and are either toxic to insects or deter insect feeding. Debate exists among researchers about whether the endophyte produces the alkaloids themselves or causes the plant to produce them.
Endophyte-infected grasses also improve drought and heat tolerance, which results in better persistence in pastures and turf stands. The mechanism is not well understood but the endophyte relationship may alter certain biochemical properties of the plant as well as enhance root growth.
In a few studies at Rutgers University, plots containing endophyte-infected Chewings, strong creeping and hard fescues showed greater resistance to dollar spot (Sclerotinia homeocarpa). This resistance mechanism is unclear because the endophyte and host plant relationship is complex. Each endophyte has different characteristics and properties; therefore, breeders use different species of endophytes for each turfgrass species.
Turfgrasses with endophytes The first turfgrass species with commercially available endophyte-enhanced seed was perennial ryegrass in the 1980s. Since then, breeders have developed many endophyte-enhanced perennial ryegrass and tall fescue varieties. Within the past five years, breeders have also commmercialized endophyte-enhanced varieties of strong creeping red, Chewings, hard and other fine fescue species.
Unfortunately, these developments are not as easy as some people may believe. A species of endophyte in the fine fescues, Epichloe festucae, causes a problem called "choke," which affects the seed stalk and consequently reduces seed production. Fortunately, this is not a problem with the endophyte Neotyphodium that infects perennial ryegrass and tall fescue. Because some endophytes cause unwanted problems with the plant, breeders must use the proper endophyte in their programs. Also, an endophyte is simply an "organism living within another plant," so not all endophytes confer benefits such as insect resistance or drought tolerance. Researchers must continue to identify the proper endophytes that help the plant without causing negative responses.
Future research - Other turfgrass species. When will we be able to buy bentgrass or bluegrass with endophyte? Rest assured, many researchers are working on this problem. However, I am not aware of any endophytes naturally occurring in creeping bentgrass or Kentucky bluegrass. Endophytes have been identified in relatives of Kentucky bluegrass (Poa spp.) and creeping bentgrass (Agrostis spp.) and research is focusing on transferring those endophytes. Researchers are using both traditional hybridization (cross-pollination) and artificial inoculation techniques with some success. However, with Kentucky bluegrass, the "choke" problem seen with the fine fescues is present.
- Toxicity to vertebrates. Other research on endophytes involves the reduction or elimination of toxicity problems in animals. This is significant to turf managers for two reasons. First, turfgrasses such as tall fescue and perennial ryegrass are also used in pastures. Endophyte-infected grasses should not be intentionally or unintentionally planted in pastures; however, they occasionally end up there. Therefore, endophytes that have insect resistance or stress tolerance, but do not exhibit animal toxicity, would be beneficial. Second, in seed production fields, burning of grass straw has been all but eliminated. Straw disposal is now a big problem for grass-seed growers and companies. Endophyte-infected grass-seed straw could provide good quality forage if the endophyte was not toxic to animals.
- Infection percentage and seed viability. One of the most important research needs is developing a quick, accurate method to determine endophyte infection percentage and viability in seed. Presently, the percentage of endophyte-infected seed can vary tremendously depending on storage conditions and the seed lot. Scientists disagree on the percentage of endophyte that needs to be present in seed for the endophyte to provide significant benefits. I would propose that at least 50 percent of the seed in a bag should be endophyte-infected and the more the better. Research at Rutgers University documented that the percentage of endophyte-infected plants in a turf stand increases over time. Presumably, this is due to the increased survival of grass plants with endophyte. Therefore, it would be helpful to know for certain the percentage of seed infected with endophyte and, for obvious reasons, whether the endophyte is dead or alive.
Having the endophyte in the seed is an obvious benefit of which you can easily take advantage. Establish endophyte-enhanced turf by planting endophyte-enhanced seed whenever possible. This gives you the opportunity to prevent some common problems associated with turfgrasses. You will be rewarded with less insect damage and possibly improved stress tolerance. Check with your local seed supplier to find out what endophytic varieties they offer.
Additional research needs to include the identification of endophytes that will survive for longer periods of time in seed and under more extreme storage conditions. Also, a better understanding of the relationship and exactly how resistance and stress tolerance occurs would be useful. If an endophyte were found that colonizes the roots of grasses and helps the plant resist feeding from grubs, this would be a major breakthrough. In summary, endophytes have provided many exciting scientific advancements and practical benefits. However, there is much more to look forward to in the future.
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