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a USDA-ARS, Crop Genetics and Production Research Unit, Jackson, TN 38301
b (retired)
* Corresponding author (amengistu{at}ars.usda.gov)
Soybean [Glycine max (L.) Merr.] germplasm line D99–2065 (Reg. no. GP-321, PI 639692) was developed by the USDA-ARS, Stoneville, MS, in cooperation with the Mississippi Agricultural and Forestry Experiment Station, Stoneville, MS, and released in 2005. Expressing resistance allele Rps-1d, this line expands the set of previously released Phytophthora rot [caused by Phytophthora sojae (M. J. Kaufmann & J. W. Gerdemann)] resistant lines, which are near-isogenic to the cultivar Bedford (Hartwig and Epps, 1978). The other released lines, each with a single different resistance allele, are D92–6487, Rps1-k; D93–8664, Rps5; D94–6041, Rps4; D95–5246, Rps3-a; D96–1217, Rps1-c; and D98–1216, Rps3-b (Kilen and Young, 1994, 1996, 1998, 2000, 2003a, 2003b) and D98–1218, Rps2 (Mengistu et al., 2005). These releases, including D99–2065, may be used to pyramid genes for Phytophthora rot resistance. Level of resistance to soybean cyst nematode (Heterodera glycines Ichinohe) races (3, 14: corresponding to HG types 0 and 1.3.6.7, respectively) is the same as their recurrent parent, Bedford. Each released line has a unique gene–allele combination in the same genetic background (Bedford) which makes them useful as diagnostic tools.
Rps1-d confers resistance to races 1 through 7, 9 through 11, 13 through 16, 18, 21, 22, 24, and 25 of P. sojae (Buzzell and Anderson, 1992). D99–2065 was developed by backcrossing the allele Rps1-d from PI 103091 into Bedford. Wu An (PI 103091), the donor of Rps1-d, was introduced from China in 1933.
Race 1 or race 2 of P. sojae was used to identify resistance. Races were verified by means of a standard set of soybean differentials [Mukden, PI 84637, D60–9647, PI 54615–1, PI 130091, Kingwa, CNS, PI 86972–1, PI 171442, PI 172901, PI 340046, PI 86050, L62–904, Williams 82, Altona, Harsoy 63, and PI 399073 (Buzzell and Anderson, 1992; Dorrance and Schmitthenner, 2000)] and breeding lines with known genes for resistance to P. sojae [FC 31745, Bedford, Freedom, Arksoy, D55–1492, D51–4863, D94–6041, D93–8664, D99–2004, and D98–1216 (Kilen et al., 1974; Kilen and Young, 1996, 1998)] and an array of P. sojae races. Seedlings were inoculated by the hypocotyl puncture method (Morgan and Hartwig, 1965). In each cycle of the backcrossing program, F2 plants were harvested. The reaction of 12 F3 plants from each F2 plant was used to identify F2 plants homozygous for resistance to Phytophthora rot. Remenant seed from homozygous resistant F2 plants were used as pollen parents. After the fourth backcross to Bedford, an F3 plant that was uniformly resistant to P. sojae was increased for three generations (F3, F4, F5) by the pedigree method (Fehr, 1993). During these 3 yr, visual selection was made to complete the recovery of the morphological type of the recurrent parent. One hundred F5 plants were inoculated with races 1 and 2 to verify the reaction of the F3. Approximately 100 plants were also inoculated with races 1 and 2 at the F8 generation. D99–2065, composited in the BC4F3:8 generation, was evaluated for reaction to HG Type 0 and HG Type 1.3.6.7 (Niblack et al., 2002) of the soybean cyst nematode at Jackson, TN, using the method described by Young (1990). D99–2065 had female index of 4 and 5 for each HG type population above, respectively.
In replicated yield tests on clay soil (Vertic Haplaquept, very fine montmorillonitic, thermic) at Stoneville, MS, in 2000 through 2002, yields of D99–2065 and Bedford were 1490 vs. 1270 kg ha–1, 2380 vs. 1010 kg ha–1, and 3740 vs. 3280 kg ha–1, respectively. The 3-yr means were 2540 kg ha–1 for D99–2065 and 1850 kg ha–1 for Bedford. The differences in yield in the 3 yr were significant at the P 
0.01 level. A breeding line [D55–1492, from (Roanoke x Rose Non-pop) x (S100 x CNS)] very susceptible to Phytophthora rot, showed symptoms of the disease all 3 yr, while D99–2065 showed no symptoms. Comparative yields on soils not prone to Phytophthora rot, however, were not measured.
D99–2065 is maturity group V and is similar to its recurrent parent Bedford for all observable traits. Both D99–2065 and Bedford have white flowers and tawny pubescence. During the 3 yr of yield testing, D99–2065 had a mean plant height of 92 cm, a lodging score of 2.6 (on a scale of 1–5), and 123 d to mature. The mean height for Bedford was 90 cm, a lodging score of 2.7, and 126 d to mature.
Small amounts of seed may be obtained from the Crop Genetics and Production Research Unit, P. O. Box 345, Stoneville, MS 38776–0345 for 5 yr for research purposes, including development and commercialization of new cultivars. It is requested that appropriate acknowledgment and recognition be made if this germplasm contributes to the development of a new cultivar. Seed of D99–2065 has been deposited in the National Plant Germplasm System.
NOTES
Received for publication May 19, 2006.
REFERENCES
This article has been cited by other articles:
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  A. Mengistu, T.C. Kilen, and P.A. Donald Registration of D95-5048 Soybean Germplasm Line Resistant to Phytophthora Rot and Soybean Cyst Nematode Races 3 and 14 Crop Sci., February 6, 2007; 47(1): 452 - 453. [Full Text] [PDF]
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