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Dep. of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078
* Corresponding author (jlc{at}mail.pss.okstate.edu)
OK 206 and OK 207 alfalfa (Medicago sativa L.) germplasms (Reg. no. GP-344, PI 619164 and GP-345, PI 619165) were developed by the Oklahoma Agricultural Experiment Station and released in 2000. These are broad genetic base populations that provide resistance to the blue alfalfa aphid (Acyrthosiphon kondoi Shinji), biotype BAOK90, and the spotted alfalfa aphid [Therioaphis herioaphis maculata (Buckton)]. OK 206 and OK 207 have demonstrated good adaptation to Oklahoma and are intended as source populations for use in alfalfa breeding programs where multiple-pest resistance should include resistance to the biotype of blue alfalfa aphid first discovered in 1990 in Oklahoma (Zarrabi et al., 1994).
OK 206 and OK 207 were developed by recurrent phenotypic selection for resistance to blue alfalfa aphids collected in Oklahoma. Parents of OK 206 and OK 207 included 7 to 16% each of the cultivars 5472 (Woodward et al., 1993), Aggressor (North American Alfalfa Improvement Conference, 2000), Apollo Supreme, Cimarron (PVP 7900062), Garst 630, Magnum III, and WL 320 (Hanson et al., 1987), and the germplasm OK 51 (Caddel et al., 1992). Parental cultivars of OK 206 also included Good As Gold (4%) and CUF 101 (17%) (Lehman et al., 1983). These cultivars and the germplasm are well adapted to Oklahoma and the southern Great Plains, with the exception of CUF 101. OK 51 and CUF 101 were the only parental sources that possessed high resistance to the original biotype of blue alfalfa aphid. Two cycles of selection for resistance to the blue alfalfa aphid BAOK90 biotype were conducted. In cycle 1, approximately 1000 plants of each source cultivar were screened using standard procedures (North American Alfalfa Improvement Conference, 1999), resulting in 81 and 61 resistant phenotypes recovered for OK 206 and OK 207, respectively. Each strain was intercrossed in the greenhouse by hand. In cycle 2, several hundred syn 1 plants each were screened, resulting in 115 and 127 resistant plants, respectively, for OK 206 and OK 207. These were also intercrossed in the greenhouse by hand to produce the syn 1 generation of OK 206 and OK 207. Syn 2 and syn 3 seed was produced in isolated field plantings, with honey bees (Apis mellifera L.) for pollination.
Seedling tests to evaluate resistance to blue alfalfa aphid were conducted at Stillwater, OK, and Johnston, IA. The percentages of seedlings exhibiting resistance to aphids collected in Oklahoma were blue alfalfa aphid—tested at Stillwater OK 206 = 45, OK 207 = 35, CUF 101 (R) = 25, and ‘Arc’ (S) = 6, and tested at Johnston OK 206 = 32, OK 207 = 22, CUF 101 (R) = 14, and Arc (S) = 3; spotted alfalfa aphid—tested at Stillwater OK 206 = 53, OK 207 = 47, ‘Baker’ (R) = 50, and ‘Caliverde’ (S) = 2 [(R) = Resistant; (S) = Susceptible].
Although specific tests for resistance were not conducted, on the basis of their parentage, OK 206 and OK 207 probably possess resistance to bacterial wilt [caused by Clavibacter michiganensis subsp. insidiosus (McCulloch)], Fusarium wilt [caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. medicaginis (Weimer) W.C. Snyder & H.N. Hans], pea aphid [A. pisum (Harris)], anthracnose (caused by Colletotrichum trifolii Bain & Essary), Phytophthora root rot (caused by Phytophthora megasperma Drechs. f. sp. medicaginis T. Kuan & D.C. Erwin.), and Verticillium wilt (caused by Verticillium albo-atrum Reinke & Berthier).
Forage yield for OK 206 and OK 207 has been tested since 1997 in several Oklahoma sites. Each trial included the best cultivars developed by public and private breeding programs. Detailed results of each forage evaluation have been distributed in Central Alfalfa Improvement Conference Variety Test Reports and are online at www.agr.okstate.edu/alfalfa/var-test/alf-var.html; verified 10 Dec. 2001. Yields of OK 206 and OK 207 have been good, but not as consistently highly productive as the best cultivars for the area.
Flower color of OK 206 and OK 207 is approximately 82% purple and 18% variegated. Both germplasms are less fall dormant than all their parents, except CUF 101. Winter hardiness has been sufficient for the germplasms to survive four winters in Oklahoma with minimal plant loss.
Fifty grams of syn 3 seed will be provided upon written request to the corresponding author and agreement to make appropriate recognition of its source when this germplasm contributes to the development of a new germplasm, cultivar, hybrid, or strain cross. Request for seed from outside the USA should be accompanied by the appropriate customs and control documents.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the assistance of Gary Hoard, Pioneer Hi-Bred International, Inc., Johnston, IA, for evaluation of this germplasm.
NOTES
Contribution from the Oklahoma Agric. Exp. Stn. Registration by CSSA.
Accepted for publication October 31, 2001.
REFERENCES
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