John Caddel 
john.caddel.@okstate.edu
Plant and Soil Sciences Department
Oklahoma State University

Many forage legumes are used in Oklahoma to some extent (Table 1). Most species are found only sparingly in pastures. Alfalfa is the only Medicago spp. that is planted on an important number of acres in the state. Arrowleaf, white, red, and rose clovers are the most commonly planted Trifolium spp. Lespedeza is the only warm-season annual normally used for pastures. Most of the other forage legumes are used for special purposes and planted on relatively few acres.

Table 1. List of forage legume used in Oklahoma.

n the eastern part of the state, several clovers (both annual and perennial) are well adapted and the main limitations to their use is desire by animal producers, not a characteristic that could be easily improved by a breeding program. In the western part of Oklahoma, the only widely grown forage legume is alfalfa, but it is used almost exclusively used for hay production. The western part of the state tends to be drier than the east, and the soils tend to be more neutral or alkaline. Soils in the west generally have higher concentrations of potassium than those in the east.

ALFALFA BREEDING

Alfalfa has been the subject of a breeding program since 1977. The most important breeding objective has been the development of multiple pest resistance in material adapted to the southern Great Plains. ‘OK 49’ was developed from Oklahoma Common sources and released in 1990. Even though OK 49 does not have high levels of resistance to some of the important pests, it has been well received by alfalfa producers and is still competitive with the best commercial cultivars in yield trials. Four other cultivars (OK 169, OK 199, OK 200, and OK 201) were released in 2000 but have not been distributed. Yield and persistence of these cultivars has been well tested in Oklahoma and is as good as any commercially available material. Winter hardiness is at least adequate for the southern Great Plains.

OK 169 is a broad gene base cultivar resulting from an equal blend of seed from seven strains, each of which was the result of interpollination of the best cultivars and experimental strains in a series of evaluations. The cultivars and experimental strains were selected for yield and persistence. During the fourth to sixth year of production, plants belonging to the best entries produced seed on-site, in old yield trials, using wild bees for pollination. At each site plots had thinned to about 2 to 3 plants/ft² in inferior entries and 4 to 5 plants/ft² in the good ones. Other entries in the tests were cut just prior to flowering to eliminate their pollen. Parentage of OK 169 traces to 26 released cultivars and germplasms and 20 unreleased experimental strains.

OK199, a moderately wide gene base cultivar, derived by strain crossing plants of three cultivars and an experimental strain (‘Cimarron VR’, ‘WL 320’, OK 49, and OK 177), all of which are well adapted to the southern Great Plains. Equal quantities of the four components were blended and planted in wide rows for seed production at Chickasha, OK, in 1992. Plants were allowed to intercross with wild bees, and syn 1 seed was harvested in bulk in summer 1993. Syn 2 and syn 3 seed was produced in subsequent years without intentional selection.

OK 200, a moderately wide gene base cultivar, is the result of strain crossing and indirect selection among and within adapted alfalfa cultivars and germplasms for pest resistance, tolerance to environmental stress, seed production, and general adaptation. Twenty entries were planted in a forage yield evaluation in 1989. By 1994, entries had thinned to 2 to 3 plants/ft² in inferior entries and 4 to 5 plants/ft² for persistent ones. KS 219, a multiple-pest resistant germplasm from Kansas, was planted in a single row around the test in 1993. The inferior entries were harvested just before flowering in 1994 so as to not contribute pollen to the strain cross. OK 200 was derived from crossing KS 219 as the female with pollen, primarily from five cultivars and four experimental well-adapted, multiple-pest resistant strains. Seed was harvested from the KS 219 plants, which were few compared to the number of plants of the male plants.

OK 201, a moderately wide gene base cultivar, was derived from strain crossing surviving plants of cultivars adapted to the southwest Oklahoma. The parent cultivars included ‘Buffalo’, ‘Cody’, ‘Cimarron’, ‘WL 318’, and ‘555’, with approximately equal contribution from each. OK 201 is the result of selecting among and within well adapted alfalfa cultivars for production and persistent in Washita Co., OK. Ten cultivars were sown in a replicated on-farm demonstration in 1987. Yield was measured on each cultivar during production years 3 and 4. By year 6 (1993) stands had thinned to about 2 to 3 plants/ft² in inferior cultivars and 4 to 5 plants ft² in the good ones. Seed was harvested from the most persistent plants in the good cultivars. Other entries in the tests were cut just prior to flowering to eliminate their pollen during seed production. This development scheme allows for simultaneous indirect selection for pest resistance, tolerance to environmental stress, seed production, and general adaptation to southwest Oklahoma while maintaining a broad gene base of old (1940’s and 1950’s) alfalfa cultivars and infusing genes from cultivars developed in the 1970’s.

ALFALFA CULTIVARS TEST RESULTS FOR OKLAHOMA

Personnel in the Plant and Soil Sciences Department through the Oklahoma Agricultural Experiment Station and Cooperative Extension Service, conduct alfalfa cultivar evaluations to assist producers with decisions related to cultivar choices. Normally five new trials are established each September. Cultivars are planted in replicated small (1 x 5m) plots, usually at research stations but occasionally in commercial alfalfa fields. Each plot is harvested and weighed at every cutting for at least 3 years. Each year, results of alfalfa cultivar tests are published and a recommended list is updated with descriptions of how they performed in Oklahoma.

The most recent summary of alfalfa cultivar performance in Oklahoma is available on the World Wide Web at www.alfalfa.okstate.edu/var-test/alf-var.html. That site includes a summary of recent testing and a recommended cultivars list. It also includes details of yields of experimental strains and released cultivars, showing yields for individual cuttings and total yields for a particular year, and a total over years of the test.

The recommended list of cultivars includes those that are well-tested and have performed well. They have been tested for at least 12 test-years. This means each cultivar has been tested for 1 to 3 years at several sites. These cultivars have the pest resistance necessary for Oklahoma, and it is highly likely these relatively new cultivars will continue to do well.

GERMPLASM DEVELOPMENT

We have developed more than 200 experimental alfalfa strains since 1977. Some of the new strains were developed for direct cultivar improvement, and others were developed for improving germplasm which could, in turn, be used for cultivar development in this or other programs. OK 51 and OK 85 germplasms were released in 1990 and possess high levels of resistance to the blue alfalfa aphid as well as other important pests. In 2000, ten other germplasms were released.

OK 163, OK 164, OK 187, OK 188, OK 189, and OK 208 were synthesized using several thousand plants originating from strain crosses of accessions (PI’s) selected through phenotypic selection for resistance to blue alfalfa aphids collected in Oklahoma. Six intermediate strains were created by saving one or two plants resistant to blue alfalfa aphids from accessions of the USDA world collection of alfalfa. Overall, 926 accessions were screened, and plants were saved from 471 accessions. An equal blend of seed from these populations were planted in an isolated field in rows. The blend of strains was planted in every other row with ‘Cimarron’ in alternate rows. Wild bees were used to pollinate. Syn 1 seeds was harvested separately from alternate rows, resulting in two types of seed. One had the world collection accessions as the female parent (OK 163), and the other had Cimarron as the female parent (OK 164). OK 163 seed was then sown in alternate rows with OK 169 (see description above). Seed was produced, and as before, two types of seed was harvested. Seed harvested from OK 163 was designated OK 187, and seed harvested from OK 169 was designated OK 188. Approximately 1000 plants each of OK 163 and OK 164 underwent two additional cycles of selection for resistance to the blue alfalfa aphid collected in Oklahoma. A mixture biotypes was used in the first cycle, resulting in 294 plants, which were intercrossed to create OK 189. Several hundred plants of OK 189 underwent a second cycle of selection for resistance to blue alfalfa aphid BAOK90, and 112 selected plants were interpollinated to form OK 208.

These germplasms possess many genes tracing to their highly diverse parentage not normally possessed by most cultivars and experimental strains in traditional breeding programs. In addition to their varying degrees of adaptation contributed by their adapted parent, they should provide some resistance to fusarium wilt, bacterial wilt, phytophthora root rot, anthracnose, verticillium wilt, spotted alfalfa aphids, blue alfalfa aphids, and pea aphids. Winter hardiness has been good enough for the most enhanced strains to survive winters in Oklahoma with no lost due to cold. Forage yield potential of these germplasms is quite variable. Those with the least crossing to an adapted parent tend to have lower yields; whereas, those with backcrosses to adapted material and several generations of natural selection while in seed production have yields nearly as high as any well-tested cultivar.

OK 190, a wide gene base germplasm, was developed by the convergence of three lines of pest-resistance breeding. Line 1: Several thousand plants of 16 cultivars and experimental strains were screened for resistance to the blue alfalfa aphid in the greenhouse, resulting in 151 plants selected. Line 2: Several hundred plants from 16 cultivars and experimental strains were screened in the greenhouse for resistance to the spotted alfalfa aphid, resulting in 291 plants selected. Line 3: In the field, several thousand plants of 5 cultivars and experimental strains were screened for resistance to the phytophthora root rot, resulting in 137 plants selected. The resulting 579 plants were transplanted and interpollinated in an isolated field using honey bees to produce syn 1 seed.

OK 206 is a moderately wide gene base germplasm resulting from two cycles of phenotypic recurrent selection for resistance to the new biotype of the blue alfalfa aphid (BAOK90). Parental sources include ‘CUF 101’, ‘5472’, ‘Aggressor’, OK 51, ‘Magnum III’, Cimarron, ‘Garst 630’, WL 320, ‘Apollo Supreme’, and ‘Good As Gold’. With the exception of CUF 101 these cultivars and germplasm are well adapted to Oklahoma and the southern Great Plains. In first cycle of selection, 81 plants were selected from the 10 sources with about 1000 plants from each subjected to BAOK90. Selected plants, exhibited resistance in standard screening procedures, were intercrossed in the greenhouse by hand to produce syn 1 seed. Several hundred plants of syn 1 were screened for resistance to BAOK90 in the second cycle of selection, and 115 selected plants were interpollinated by hand in the greenhouse to produce syn 1 seeds of OK 206. Syn 2 and syn 3 seed for both strains were produced in the isolated field using honey bees for pollination.

OK 207 is a moderately broad gene base germplasm resulting from two cycles of phenotypic recurrent selection for resistance to the new biotype of the blue alfalfa aphid (BAOK90). Parental sources were the same as OK 206 except CUF 101 was not included in an effort to improve the winter hardiness and fall dormancy.

OK 212 was developed by phenotypic selection for resistance to the blue alfalfa aphid, biotype BAOK90, in the cultivar WL 457. About 120 syn 0 plants that exhibited resistance to the blue alfalfa aphid collected in Oklahoma were transplanted to an isolated field plot and intercrossed using wild bees. Syn 1 seed was harvested and planted in a larger isolation block for syn 2 seed production.

Future of Alfalfa Breeding at Oklahoma State University: We have no present intentions of developing new experimental strains or new cultivars. Anyone interested in using any of our released or unreleased germplasm for additional breeding work should contact the author.

BREEDING OTHER FORAGE LEGUMES

In the mid 1990’s we initiated a breeding program for other forage legumes species for Oklahoma and other areas of the Upper South and/or in the southern Great Plains. To address which species to include, we took into account areas that presently had an array of forage legumes for use in pastures and for hay. We considered all the species listed in Table 1 but wanted to avoid duplication of other breeding programs.

White clover is the most resilient and productive for the eastern part of the state. It was decided that we should examine other cultivars as they are released, but no white clover breeding program would be initiated. Red clover is well adapted to much of the state. Its main weakness is short stand life. Red clover breeding will be limited to cultivar evaluations and intercrossing surviving plants as stands thin in the evaluation tests.

Arrowleaf clover has been the most productive and reliable annual clover for the eastern part of the state for about 30 years; however, it has been noted that arrowleaf clover stands are not as productive as they were 10 years ago. A major problem seems to be virus diseases carried by aphids. It was decided to work toward the development of aphid resistant arrowleaf clover and the development of arrowleaf clover for the western part of the state. Rose clover, developed in Texas, seems to be well adapted to most western Oklahoma pastures, but arrowleaf clover is productive much longer into the late spring than rose clover. Some preliminary studies showed rigid medic (Medicago rigidula) to have many desirable traits for Oklahoma pastures, and it will be subjected to genetic improvements.

Several forage legumes are naturalized and are found throughout large parts of the state. It was decided to devote some effort to examining the possibilities of improving some of these species. This group includes black medic, burr medic (burclover), button medic (buttonclover) hop clover, and rabbitfoot clover.

The following are the results of some of our preliminary activities with forage legumes. Table 2 includes yield data from four perennial forage legume species. Forage was cut with a fail harvester, leaving a stubble height of 3 to 4 inches, except white clover stubble was 1 to 3 inches. Red clover dry matter production was good in all environments. Most of the red clover stands were so thin after two years of production that additional yield measurements would have been difficult because of weeds. White clover stands were thick at the end of two years at Stillwater and Perkins but thin at Chickasha (driest site). White clover yield was probably an underestimation of what cattle would have grazed. The fact that sainfoin and cicer milkvetch do not cause bloat in ruminants is their strongest trait. Their yields and persistence in these sites was not as good as the clovers or alfalfa in adjacent areas.

Table 3 summarizes the yield of four annual forage legumes planted in September, 1997 at three locations. It shows that rigid medic (M. rigidula) ‘3076’ has a good potential. Observations of rigid medic interseeded in grass pastures indicate it reseeds itself well and has adequate winter hardiness for Oklahoma. Arrowleaf clover’s yield was variable, but generally high. ‘Joe Burton’ berseem clover grew well until the first freezing temperatures; whereas, ‘Bigbee’ was killed at Chickasha and Perkins but not at Stillwater

Table 4 summarizes some of our arrowleaf clover work. In an effort to determine if arrowleaf clover could adapt to western Oklahoma, we harvested seed from old (more than 10 years) stands near the middle of the state and planted the seed in isolations to produce two populations which were advanced to the syn 3 generation. In September 1997 these two experimental strains were planted in plots with ‘Yuchi’, the parent cultivar for both populations. At all three locations Yuchi yielded much less than the strains. During the spring 1998 all the Yuchi plots had moderate to severe symptoms of viruses; whereas, the selections had only light symptoms that developed late. During the spring of 1998 pea aphids were present in high populations at all three sites.

In September, 1998, we planted the two selected strains along with the same source of Yuchi seed and a new source of Certified Yuchi seed. In 1999 the selected strains yielded better than the “old” source of Yuchi but no better than the new Yuchi. In 1999 pea aphid populations developed later and were not as severe as the previous year. Virus symptoms also did not develop to the extent of the previous year. We have not confirmed that the selected arrowleaf clover strains have resistance to the pea aphids and that the pea aphids served as a vector for the virus(es). Why the new source of Yuchi yielded higher than the old source has not been determined.