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204 Curtis Hall, USDA-ARS Plant Genetics Research Unit and Department of Agronomy, University of Missouri, Columbia, MO 65211
* Corresponding author (David_Willmot{at}agilent.com)
Maize (Zea mays L.) germplasm lines Mo48 (Reg. no. GP-377, PI 634206) and Mo49 (Reg. no. GP-378, PI 634207) are yellow endosperm, dent inbred lines in the maturity group AES 800 developed for European corn borer (ECB, Ostrinia nubilalis Hübner) resistance by the Plant Genetics Research Unit of the USDA-ARS in cooperation with the Missouri Agricultural Experiment Station, University of Missouri-Columbia. Development of both releases began in the winter of 1978–1979 with crosses made in Hawaii by Cargill, Inc. and they were released in November 2003.
Mo48 was derived from the cross NC33 x B52. NC33 (PI 608538) is a selection from ‘Cokes Prolific’ (GRIN, 2003) and is moderately susceptible to second-generation ECB stalk tunneling damage (ECB2). B52 (PI 550454) (Russell et al., 1971) was derived by USDA-ARS and Iowa State University from an unknown private seed source and is highly resistant to ECB2. Selections from NC33 x B52 were manually infested in the leaf whorl with approximately 160 ECB neonate larvae per plant to evaluate resistance to first-generation feeding (ECB1) (Guthrie et al., 1960). At least three pollinations were made in each S1 family using approximately 20 tassels from a balanced bulk of the other selections. Sixty neonate larvae were infested twice within four days into or near the ear leaf axel at anthesis to assess ECB2 resistance to sheath feeding and stalk tunneling damage by splitting stalks at maturity and selecting for minimal tunneling. The best three ears of the most resistant rows were recombined in the winter nursery without ECB infestation to complete one cycle of selection per year for six cycles. This was followed by ear-to-row pedigree selection through the S6 generation with ECB pressure on the odd-numbered generations. The best of three self-pollinated selections from the best rows were continued each generation. Mo48 has been observed to be stable for resistance to ECB since bulking seed at the S6.
Mo49 was derived from a broadly based synthetic comprised of ‘Mo ECB selection 1’ through ‘Mo ECB selection 6’ crossed in all combinations to three exotic Cargill populations acquired from E.E. Gerrish (1980): Cargill 4 (adapted Caribbean material), Mexico 2, and Mexico 3. S1 selections from these crosses were planted ear-to-row, infested with ECB, and three plants pollinated by a bulk of the other selections. Half-sib recurrent selection was performed, as described above, for six cycles. The improved population was then crossed with MpSWCB#4, acquired from Frank Davis, USDA-ARS, Starkville, MS. MpSWCB#4 was selected for resistance to the southwestern corn borer, Diatraea grandiosella (Dyer) (SWCB). Recurrent selection then resumed at Columbia, MO, for four cycles based on SWCB resistance and ear type. In 1984, 2000 plants were screened for ECB2 resistance and 70 bulked for random mating in the winter nursery. This was continued five additional cycles. Finally, pedigree selection was followed through the S6 generation. Mo49 has been observed to be stable for ECB resistance and type since bulking.
Mo48 has dark green, medium-wide leaf blades angled open at about 60 degrees from the vertical. The cob is white, anthers are yellow, trace color on the glumes, and no glume bar. It has 19 to 21 tassel branches with a 23-cm spike. It has few tillers and floral synchrony is good.
Mo49 has medium green leaves possibly with lesion mimic syndrome. Leaves are medium in width and angled upright at about 30 degrees from the vertical. The cob is white, anthers are purple, glumes are striped, and there is a glume bar. Mo49 has 5–11 tassel branches with a 30.5-cm spike. It sometimes produces a few tillers and silking is slightly delayed.
In 1999, Mo48 and Mo49 were at least as resistant as the resistant checks Mo47 (Barry et al., 1995) and CI31A in replicated trials in MO, NE, IA, and MS. In 2001, for ECB2 stalk tunneling length, the most important measure of resistance, Mo48 and Mo49 were not significantly different (P < 0.05) from the best check, Mo47 (2.5, 4.7, and 3.8 cm, respectively). In 2002, the inbreds were part of multi-state, three replication tests in MO, MS, NE, IA, IL, OH, and DE for a total of 11 ECB1 locations evaluated and 10 for ECB2 with Mo47 used as a resistant check. Mo48, Mo49, Mo47, and B73 had ECB2 stalk tunneling lengths of 10.6, 7.0, 8.3, and 29.1 cm, respectively, which were all significantly different at P < 0.05. In 2001 and 2002, testcrosses were evaluated in five Missouri environments. Both Mo48 and Mo49 yielded more on a Mo17 tester than on B98, which has BS11 background (Lamkey and Hallauer, 1997). Therefore, these releases should be useful to improve highly ECB-susceptible Stiff Stalk Synthetic–derived inbreds. Mo48 x Mo17 and Mo49 x Mo17 averaged 4857 and 4101 kg ha–1 vs. 5603 kg ha–1 for the check B73 x Mo17. The Mo49 testcross was significantly lower in yield (P < 0.05) while the Mo48 testcross was not lower than the check. Stalk tunneling length for these three crosses averaged 5.7, 4.1, and 8.4 cm, respectively with the check being significantly more damaged (P < 0.05). For plant and ear height means in Missouri in 2001 and 2002, Mo48 averaged 175 and 83 cm tall; Mo49 averaged 143 and 62 cm vs. Mo17 at 187 and 98 cm, respectively. In some environments, Mo49 had slightly more lodging than the other entries due to its thin stalk. Among the lines tested for possible release, Mo48 had the best combination of yield (especially with the Mo17 tester) and ECB2 tunneling resistance. Mo49 had the highest level of resistance—equal to or better than that of Mo47.
Seed from the S6 generation of Mo48 and Mo49 is available in lots of 50 kernels and may be obtained from the Plant Genetics Research Unit, USDA-ARS, 204 Curtis Hall, University of Missouri, Columbia, MO 65211. They are on deposit in the National Plant Germplasm System. We ask that appropriate recognition be given when this germplasm contributes to research or to a new cultivar.
ACKNOWLEDGMENTS
We acknowledge the assistance of J. Barry, T. Praiswater, and C. Thiel in the development of these inbreds.
NOTES
Accepted for publication July 31, 2004.
REFERENCES
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