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Bermudagrass is a complex of interbreeding species undergoing rapid evolution through natural selection and human intervention. Collectively, bermudagrasses include low-growing turf varieties, pasture varieties, wild relatives, derived mutations, and some of the world's worst weeds. Bermudagrasses are the primary grass on Florida golf courses. Important issues for golf course managers to understand are variety selection and identification, and management of genetic off-types. Hybrid bermudagrass varieties make Florida golf courses among the best playing surfaces in the world. But in the 1920's they were planted to Arizona-grown, probably Common, bermudagrass seed (Dr. Roy Bair, personal communication). Common bermudagrasses are coarse-textured, seedy, and poor for play. According to Carrier ("Florida greenkeeping." The National Greenkeeper 1(10):19-20. 1927), Florida golf courses were "built largely to meet the demand of the northern tourists who sojourn there for a few winter months," when Florida courses were overseeded with cool-season grasses. Today's hybrids provide increased shoot density and finer leaf texture compared with Common. Hybrids can be mown closely enough for a primary playing surface on greens, tees, and fairways. Although hybrid bermudagrasses turn off-color when temperatures dip below 12 C (54 F), they provide at least sporadic winter growth throughout Florida, and do not have pronounced dormancy. In Florida, overseeding is often avoided south of Lake Okeechobee, thanks in part to the use of hybrids and mild temperatures. Since release of the first hybrid bermudagrass in the U.S., 'Tiffine' in 1953, breeders have provided a slow stream of new hybrids, as well as improved seeded varieties. The most successful work has come from the USDA Coastal Plain Experiment Station, Tifton, Georgia. From Tifton, Dr. Glenn W. Burton and his colleagues released the hybrids 'Tifway' (T-419) in 1960 and 'Tifdwarf' in 1965, which remain among the best golf course grasses in 1998. Classical Theory of Hybrid Bermudagrass The classical theory of improved hybrid bermudagrasses is
that initially there was a 36-chromosome (Fig.
1) Common bermudagrass species (Cynodon dactylon)
and an 18-chromosome African bermudagrass (Fig.
2) species (C. transvaalensis). Chromosomes
are small cellular structures that carry most of the genes and are
part of the inheritance machinery and a tool for variety identification.
'Tifway' was discovered as a 27-chromosome plant, appearing first
as a seedling grown from a shipment of 36-chromosome bermudagrass
seed from Africa. Because of its 27 chromosomes and its fine
texture, 'Tifway' was deduced to have had an unknown 18-chromosome
male parent, apparently C. transvaalensis, but to
have shared the same 36-chromosome female parent with other seedlings
in the shipment (Fig. 3). This would make
'Tifway' an interspecific ("between different species")
hybrid.
Artificial crosses between 18- and 36-chromosome plants have supported this theory. These hybrids also have 27 chromosomes, and characteristics intermediate between parent species, similar to 'Tifway.' Depending on choice of parents and other factors, upright grasses such as 'Tifway' can be produced, as well as more prostrate greens varieties. An example is 'Tifgreen,' a greens variety released in 1954. Because 27 is an odd chromosome number, representing partially matched genetic bundles from each parent, it is unlikely that 'Tifway' and other hybrids can produce viable pollen, eggs, or seed, even though they produce seedheads. Although hybrids are sterile, they are not evolutionary dead-ends, as mutations can occur and can be propagated vegetatively. For example, 'Tifway II' bermudagrass, released in 1981, was created by gamma irradiation of Tifway; thus it was an artificial vegetative mutation. 'Tifway II' has an apple green color (Fig. 4) which creates a mottled appearance in combination with a contaminant that was present in the release stock. A newer release, 'TifEagle,' is a greens variety derived as an artificial mutation from 'Tifway II,' which shows the power of mutations to drastically change a variety. Most mutations are harmful to plant survival, and of the few successful mutations, some, which show up first, have aggressive and weedy characteristics. It takes skill and patience to recognize a truly superior new bermudagrass, whether it was created artificially or naturally. The most important golf course grass in Florida, 'Tifdwarf,' was apparently a naturally occurring mutation from 'Tifgreen' (T-328). 'Tifgreen' was an early 27-chromosome hybrid sent out for testing in 1954, and it is still useful on golf course tees and as a collar barrier to prevent encroachment of fairway grass onto 'Tifdwarf' greens. Other new greens grasses continue to arise from apparent off-types of 'Tifgreen' and 'Tifdwarf,' including Quality Dwarf, Classic Dwarf, PF-11, FloraDwarf, and Champion. Because of their similar characteristics, one of us (Busey) referred to these as "Ultradwarf" bermudagrasses, and, for better or worse, the name stuck. While these plants generally have shorter internodes than Tifdwarf, and seem tolerant of the same low cutting heights as Tifdwarf, the concerns are that they not be taken too low, and that their environmental range is not as well known as the earlier releases. Evidence in USDA Plant Introduction records shows that throughout most of the 20th century, superintendents in the Republic of South Africa maintained and named distinctive types of bermudagrass from their greens, probably including mutations of naturally occurring hybrids. The endless appearance of new bermudagrasses on greens is therefore a worldwide phenomenon. Variations are an exciting source of potential new varieties (Fig. 5), but a great frustration for the superintendent who would rather have the entire green in a single variety, than a breeding operation. Some corrections and qualifications are needed to the classical theory of hybrid bermudagrass. Semantically, "Common" bermudagrass can refer to a specific variety, 'Arizona Common,' it can refer to sources of unknown variety, and (in our usage) it can refer to any 36-chromosome bermudagrass. The expression "hybrid" is misleading, because all organisms are hybrids, whether between species (interspecific) or within the same species. In many crops "hybrid" refers to artificial hybrids, but in turf bermudagrasses, its usage is for 27-chromosome plants. Since bermudagrass species interbreed, even the distinction between C. dactylon and C. transvaalensis is poorly defined as there are documented reports of 18-chromosome plants of C. dactylon. Consistent Greens and Fairways
Unfortunately, the worst weed in bermudagrass is bermudagrass (Fig. 6). When off-type bermudagrasses occur, initially as seedlings, mutations, or contaminants from other varieties, they spread. On closely mown surfaces, especially greens, off-type bermudagrasses can look distinctively different from the surrounding matrix grass (Fig. 7), but at other times they may go unrecognized. The most critical time for watchfulness is during grow-in, when aggressive types can gain the upper hand. When 'Tifway' was released, superintendents recognized it to be relatively nonaggressive and slow-growing (Mr. Ralph W. White, personal communication). Over decades of production, some producers unknowingly experienced a transition to more aggressive bermudagrasses (Fig. 8), and superintendents, naturally more watchful of the greens, were unaware or unconcerned with what was happening on the fairways. 'Tifway,' which is a fine-textured upright grass with numerous fine leaf hairs (Fig. 9) was replaced in large measure by 'Ormond' bermudagrass (Fig. 10), and other varieties, named and unnamed, throughout most golf courses in Florida. Areas containing a mixture of bermudagrasses can be injured by herbicides in places (Fig. 11) and some herbicide labels have application instructions written specifically to a particular variety Off-type bermudagrasses are more competitive, for at least part of the year; thus they gain an advantage over several growing seasons. The appearance of off-types is initially an esthetic problem. When the problem becomes severe, greens putt inconsistently, grass patches on fairways are differentially damaged by chemicals, stoloniferous patch grasses become hydrophobic (water repellent), and there can be an overall decline in the quality of the course. Even when off-type patches do not affect play, they can be a psychological factor on the minds of club members who compare courses (Fig. 6). Much breeding work is concentrated on improved seeded varieties. So far, all that have been tested through the National Turfgrass Evaluation Program (NTEP) fail to perform consistently as well as the better hybrids. This information must be treated cautiously, however, because conditions on golf courses vary from the research locations where the tests were done. The NTEP tests are done in relatively small plots with no shade, no traffic, and most of the data is collected during the first few years, some locations not even completing the whole 5 years of the test. Some of the major factors in managing bermudagrass (sting nematodes, thatch, and compaction) do not become problems for two or more years after planting Since the problem of off-types (from seedlings, mutations, or contamination by other varieties) is so widespread, a further argument can be made for seeded varieties on fairways. They are usually more aggressive and already genetically heterogeneous. In that theory, seeded varieties should be stronger in preventing appearance of off-types, because they are already heterogeneous. Such a hope may be unfounded, however, because the running growth of bermudagrass forms circular clones, which allows more aggressive ecotypes to become dominant and distinctive. Alternatively, if there are non-flowering 36-chromosome bermudagrasses, and they are not too aggressive, they will have a place. There is competition to prove that one variety is best, or at least generate a purchase decision. Superintendents have a very difficult choice to separate fact from hype. Part of the problem is that no one can tell how a grass will perform in the long haul. The world's most accomplished turf breeders have had notable failures, in fact a list of all the varieties developed by competent, qualified breeders shows very few are still in the market (Table 1). Although there are clearly differences among newer varieties, and one might even say that one is better than another under certain circumstances, the biggest factor cannot be measured. It is risk. As in other areas of life, golf courses vary in their acceptable risk-reward equation. By "golf courses" we mean members, greens committees, corporate owners, superintendent and her staff, architect, and golfers. All these people stand to win or lose based on choice of a grass variety. It is a daunting task. Rather than take the easy way out, and choose the same Tifway and Tifdwarf that have performed well in the past, a few courses choose to try something that has never been tried on a large scale before. The reward from this decision, even a failed decision, is that the golfing community as a whole can learn from the experience. Most of the risk, however, falls on the few who are willing to accept it. The biggest risk in choosing a grass for the Florida golf course is in getting a pure planting source. Mutations may occur some years down the road, and there is nothing known that can be done to prevent them. But off-types are more frequently seen within two years of planting, and are often attributable directly to planting source. Know your supplier! Specify State Certified sprigs and/or sod when they are available, and demand to receive original, official State tags. Inspect production fields, remembering that at most you might only see a small part of the problems, if any exist. Establish a clear understanding, both with the supplier and the golf course, as to what will be accepted. Finally, inspect the grow-in on a daily basis, and mark and remove off-types that are observed.
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