Dent Corn Populations

Dent Corn Breeding Populations

For Use As Genetic Stocks By Corn Breeders

BS35 is a synthetic cultivar of corn developed by intermating 19 selections that included 75% temperate and 25% sub-tropical germplasm. Selections were based on evaluations of 390 backcrosses per se and testcrosses of 80 selected backcrosses; LH185 was the tester. BS35 would be included in the Iowa Stiff Stalk Synthetic heterotic group.

BS36 is a synthetic cultivar of corn developed by intermating 13 selections that included 75% temperate and 25% sub-tropical germplasm. Selections were based on evaluations of 294 backcrosses per se and testcrosses of 62 selected backcrosses tested at five Iowa locations; LH198 was the tester. BS36 would be included in the non-Iowa Stiff Stalk Synthetic heterotic group.

BS37 is a synthetic cultivar of corn developed by intermating 20 selections that included 75% temperate and 25% sub-tropical germplasm. Selections were based on evaluations of 486 backcrosses per se and testcrosses of 100 selected backcrosses tested at seven Iowa locations; LH185 was the tester. BS37 would be included in the Iowa Stiff Stalk Synthetic heterotic group.

BS38 is a synthetic cultivar of corn developed by intermating 16 selections that included 75% temperate and 25% sub-tropical germplasm. Selections were based on evaluations of 405 backcrosses per se and testcrosses of 81 selected backcrosses tested at seven Iowa locations; BS38 would be included in the non-Iowa Stiff Stalk Synthetic heterotic group.

BS11(5-S1)C5 was developed by five cycles of S1 recurrent selection. The general procedure was to self approximately 50 S0 plants in the winter nursery. Twenty-five random S1 ears with adequate seed set were retained for inclusion in the yield trials. Remnant S1 seed of the five selected lines was intermated in the winter nursery using the bulk-entry method. The resulting Syn-1 population was random mated, by chain sibbing 300 to 400 plants, to form the Syn-2 population. The Syn-2 population was used to initiate the next cycle of selection. Two years were needed to complete one cycle of selection. This procedure was repeated until the BS11(5-S1)C5 Syn-2 population was formed. Progress from selection has been evaluated through Cycle 4. The BS11(5-S1)C4 population is significantly lower yielding than BS11C0, probably because of inbreeding depression due to small effective population size.

BS11(10-S1)C5 was developed by five cycles of S1 recurrent selection by using a procedure similar to that used to develop BS11(5-S1)C5. The main difference is that 50 lines were evaluated from each cycle and the best 10 selected lines were intermated to form the next cycle population. The BS11(10-S1)C4 population has been significantly improved, in comparison with BS11C0, for all agronomic traits. The important improvements were increased grain yield, lower grain moisture at harvest, increased resistance to stalk lodging, and earlier silk emergence.

BS11(S1)C5 was developed by five cycles of S1 recurrent selection by using a procedure similar to that used in BS11(5-S1)C5. The major difference was that 100 progenies were evaluated and the best 20 selected lines were intermated to form the next cycle population. The BS11(S1)C5 population is agronomically one of the best populations of the group. Grain yield of BS11(S1)C5 is similar to BS11(10-S1)C4 and is slightly wetter at harvest, but has significantly greater resistance to root and stalk lodging, lower plant and ear heights, and has earlier silk emergence.

BS11(30-S1)C5 was developed by five cycles S1 recurrent selection using a procedure similar to that used for BS11(5-S1)C5. The major difference was that 150 progenies were evaluated and the best 30 selected lines were intermated to form the next cycle population. The BS11(30-S1)C4 population is similar to BS11(10-S1)C4 for grain yield and other agronomic traits, except that it has slightly earlier silk emergence.

BS11(S2)C5 was developed by five cycles of S2 recurrent selection. The general procedure was to self 200 to 300 S0 plants in the winter nursery. The following summer the S1 lines were grown ear-to-row in the breeding nursery. All rows were inoculated at the 8- to 10-leaf stage with European corn borer larvae [Ostrinia nubilais (H � bner)] and rated prior to anthesis for resistance to whorl-leaf feeding. Generally, 30 to 50 percent of the lines were discarded prior to anthesis on the basis of resistance to whorl-leaf feeding and other agronomic traits such as plant and ear height, disease resistance, etc. Three to five plants were self-pollinated in the remaining lines. At harvest, seed from an ear of a single plant was kept for inclusion in yield trials. Criteria for choosing among pollinated plants within a row included seed set, ear rots, and lodging. Remnant S2 seed of the 20 selected lines was intermated using the bulk-entry method. the resulting Syn-1 population was random mated, by chain sibbing 300 to 400 plants, to form the Syn-2 population. The next cycle of selection was initiated by using the Syn-2 population. Three years were needed to complete one cycle of selection. This procedure was repeated until the BS11(S2)C5 Syn-2 population was formed. The BS11(S2)C4 population is the highest yielding population of the group. For other agronomic traits, the population is similar in performance to BS11(30-S1)C4, except that it is more resistant to stalk lodging and has earlier silk emergence.

BS11(MER)C5 was developed by five cycles of modified ear-to-row selection. The procedure was similar to the one suggested by Compton and Comstock in that there was selection on both the male and female gametes and two years were needed to complete one cycle of selection. Progenies were developed for the first cycle of selection by harvesting ears from a population allowed to open-pollinate in isolation. One-hundred ears were harvested and planted in yield trials the following year. The 20 selected lines were intermated by planting remnant half-sib seed ear-to-row in isolation as females and planting a bulk of the 20 selected lines as the male. Five ears, selected on the basis of grain yield and other agronomic traits, were harvested from each of the 20 female rows. The one hundred ears were planted in yield trials the following year as the evaluation phase of the next cycle of selection. The Syn-1 population was formed by harvesting an equal number of ears (10 to 15) from each female and bulking equal quantities of seed from each ear. The resulting Syn-1 population was random mated, by chain sibbing 300 to 400 plants, to form the Syn-2 population. The BS11(MER)C5 population is similar in performance to BS11(S2)C4, except that it has slightly taller plant and ear heights, and has later silk emergence.

BS11(HI)C5 was developed by five cycles of half-sib selection using the inbred tester B79. The general procedure was to self 200 to 300 S0 plants in the winter nursery. The resulting S1 lines were planted ear-to-row in the summer breeding nursery. The lines were inoculated with European corn borer larvae and evaluated for resistance to whorl-leaf feeding prior to anthesis. Approximately 30 to 50 percent of the lines were discarded prior to anthesis. Two plants in the remaining lines were selfed and crossed to four plants of B79. At harvest, only one selfed ear and the corresponding testcross seed was kept for evaluation. Remnant S1 seed of the 20 selected lines was intermated using the bulk-entry method. The resulting Syn-1 population was random mated, by chain sibbing 300 to 400 plants, to form the Syn-2 population. The next cycle of selection was initiated by using the Syn-2 population. Three years were needed to complete one cycle of selection. This procedure was repeated until the BS11(HI)C5 Syn-2 population was formed. Grain yield of BS11(HI)C4 was not significantly different from BS11C0, improvements were made for other agronomic traits.

BS11(FS)C5 was developed by five cycles of intrapopulation full-sib selection. For the first cycle of selection, full-sib families were developed in the winter nursery. The following summer, 100 full-sib families were evaluated and the best 20 families were selected. Remnant seed of the 20 selected full-sib families was self-pollinated in the winter nursery to produce S1s of the full-sib families. The following summer, the S1 full-sib families were intermated using the bulk-entry method. Simultaneously, full-sib families were developed for evaluation for the next cycle of selection by making up five sets of reciprocal full-sibs per pair in the bulk-entry intermating. Thus, one cycle of selection was completed in two years. BS11(FS)C5 was not significantly higher yielding than BS11C0. BS11(FS)C5, however, was significantly lower than BS11C0 for grain moisture at harvest, had increased resistance to root and stalk lodging, had lower plant and ear heights, and was earlier to silk. The following synthetic stocks are available at $50 for 500 kernels, postage paid. A brief description of each follows:

This synthetic was developed by recombining the following 10 inbred lines: B49, B50, B52, B54, B55, B57, B68, C.I.31A, Mol7, and SD10. Only one of these lines, B68, has any relationship to inbred lines derived from Iowa Stiff Stalk Synthetic. Recurrent selection, based upon S1 line evaluation was used for 5 cycles to improve this synthetic for resistance to both the first and second generations of the European corn borer. In all cycles, evaluations of the S1 lines were made in separate experiments by using artificial infestations of the first and second generations of the corn borer. The improved synthetic, BS9(CB)C5, is highly resistant to first-generation corn borer and resistant to second-generation corn borer. Also, it is slightly earlier than the original BS9.

A synthetic that was developed by 10 cycles of reciprocal full-sib selection for yield from BSTE ( Iowa 2-ear Synthetic #I) with PHPRC, also a 2-ear synthetic, as the tester. Eighteen S5 lines of the superior yielding S4 x S4 hybrids and 6 additional lines that had good stalk quality and resistance to leaf feeding by the European corn borer, Ostrinia nubilalis (Hubner), were intermated to form the Cl population. The C2 to C10 populations were developed by intermating 20 S1 lines, which were the parents of the 20 superior yielding full-sib progenies originating from the previously selected populations. BS10(FR)C10 is superior to BSTE in yield, prolificacy, and stalk quality.

An improved population of an open-pollinated variety known as Alph. Alph is an extremely variable, long-eared variety from southern Iowa, and does not resemble any of the open-pollinated varieties in our collection. Recurrent selection for specific combining ability with inbred B14 as the tester has been used for 8 cycles to improve Alph. The hybrid yield performance of BS12(HI)C8 x B14 is comparable to commercial single-crosses. Also, BS12(HI)C8 adds valuable genetic diversity to the maize germplasm pool of the North Central Corn Belt.

This improved breeding population was developed from Iowa Stiff Stalk Synthetic (BSSS) by 14 cycles of recurrent selection for increased yield. Seven cycles of recurrent selection for general combining ability for yield with Ial3 double cross [(L317 x BL349) x (BL345 x MC401)] as a tester in BSSS(HT) were followed by a cycle of full-sib selection for corn borer resistance, cold tolerance and prolificacy. This improved breeding population was redesignated BS13(S) and 4 cycles of S2 selection and 2 cycles of S1 selection have been completed. Screening among and within S1 lines for corn borer resistance and stalk-rot resistance was done in selecting elite material for the S2 yield trials. BS13(S)C5 combines well with BS12(HI)C8, BS18, BSCBI(R)C12, and BSSS(R)C12.

Four cycles of recurrent selection based on evaluations of S1 lines in replicated experiments were used to improve BS16(S2)C2 for resistance to first and second generations of the European corn borer. BS16 was developed by 6 cycles of mass selection for adaptiveness in 'Eto Composite', and BS16(S2)C2 was obtained by 2 cycles of recurrent selection for yield, based on S2 line evaluations in replicated experiments. In successive cycles of recurrent selection for resistance to corn borer, we evaluated 226, 225, 295, and 200 S1 lines and recombined 22, 22, 30, and 30 lines to give the successive improved populations. In the final cycle of selection, the average rating of all S1 lines for first generation larval feeding was 2.8 (1.0 = highly resistant, 9.0 = highly susceptible) and the range was 2.0 to 8.1. The resistant and susceptible checks rated 2.0 and 7.3, respectively. For larval feeding by the second generation, the average rating for all lines was 2.9, and the range was 2.0 to 7.3. The resistant check rated 2.0, and the susceptible check rated 9.0. The 30 S1 lines selected for recombination rated 2.0 for first generation and 2.4 for second generation. Consequently, BS16(CB)C4 is expected to have a high level of resistance to the European corn borer for the whole life of the plant. This population is not expected to be a good source for new commercial inbred lines because, with self-pollination, the inbred progenies show too much inbreeding depression and susceptibility to root lodging. However, because the original source, ETO Composite, has a Latin American origin, it is expected that resistance to European corn borer will be conditioned by some different genes than condition the resistance in BS17(CB)C4. Therefore, it can be used to obtain lines that have different resistance genes than are present in U.S. Corn Belt germplasm.

Four cycles of recurrent selection based on evaluations of S1 lines in replicated experiments were used to improve the original BS17 for resistance to the first and second generations of European corn borer. BS17 is an Iowa Stiff Stalk Synthetic population (BSSS) that was developed by composite crossing of 6 versions of BSSS, each of which has been improved for one or more agronomic traits (yield, resistance to first generation corn borer, resistance to stalk rots, and tolerance to corn rootworms). Artificial infestations by first- and second-generation corn borer in separate experiments were used to evaluate the S1 lines for resistance to feeding by the corn borer larvae. Numbers of lines evaluated in the successive cycles were 500, 300, 300, and 280, and 30 selected lines were recombined in each cycle to give the improved populations. A selection index comprised of resistance to each generation and days to anthesis was used to select the lines; grain yield of the S1 lines was an added trait to the selection index in the fourth cycle. In the final cycle of selection, the average rating of all S1 lines for first-generation feeding was 2.0 (1.0 = highly resistant, 9.0 = highly susceptible), whereas a susceptible check rated 6.2. Also, the same S1 lines had an average rating of 3.3 (range 2.0 to 6.1) for second-generation feeding. The resistant check, inbred B52, rated 2.0. The average second-generation rating for 30 selected lines was 2.3; consequently, BS17(CB)C4 is expected to have a high level of resistance to the European corn borer for the whole life of the plant and should be an excellent breeding population. The selected S1 lines in the successive cycles have been continued in the inbred line development program and several have shown good hybrid performance.

This population was developed by intermating BSK(S)C7 and BSK(HI)C7, which are two subpopulations of BSK. BSK is a strain of the open-pollinated variety "Krug Yellow Dent" that was developed at the Nebraska Agriculture Experiment Station. S1 and half-sib recurrent selection were initiated in BSK in 1953. After 7 cycles of S1 [BSK(S)C7] and half-sib [BSK(HI)C7] recurrent selection, BS18 was developed by intermating 375 plants of BSK(S)C7 and BSK(HI)C7. After the initial crosses, random matings were made by use of controlled hand pollinations in 500 to 1,000 plants for 3 generations. BS18 has good performance as a variety and good combining ability with improved strains of Iowa Stiff Stalk Synthetic. BS18 should be a useful source for the development of new lines in applied breeding programs.

The corn breeding population, BS19(S)C2, was developed from a synthetic that has been designated as Iowa Early Rootworm Synthetic in experimental studies. The original synthetic was developed by combining the following 12 inbred lines: W153R, A239, A251, A265, A297, A417, A556, A632, Msl97, Oh43, R168, and SDIO. A large number of inbred lines was evaluated for corn rootworm tolerance and root traits. These 12 inbreds were selected as parent lines for an early Iowa Synthetic to be used for further studies in resistance or tolerance to corn rootworms. Recurrent selection based on the evaluation of S1 lines in replicated experiments was used for 2 cycles, resulting in the C2 population. Traits evaluated were root damage from larval feeding, root lodging, root size, and secondary root development. This C2 population should be an excellent source from which breeders can extract early inbred lines that have good tolerance to corn rootworms. The maturity classification is approximately AES500.

Population BS20(S)C2 was developed from a maize synthetic that has been designated as Iowa Late Rootworm Synthetic in experimental studies. The following 12 inbred lines were combined to develop this synthetic: B14A, B53, B59, B64, B67, B69, B73, N6, N28, R101, HD2286 (BSSS sel.), and 38-11. Following an evaluation of a large number of inbred lines for corn rootworm tolerance and root traits, these 12 inbreds were selected as parent lines for a late Iowa synthetic to be used in further studies in resistance or tolerance to corn rootworms. Recurrent selection based on the evaluation of S1 lines in replicated experiments was used for 2 cycles, resulting in the C2 population. Traits evaluated were root damage from larval feeding, root lodging, root size, and secondary root development. This synthetic has above-average general combining ability for yield and excellent resistance to root and stalk lodging. The maturity classification is approximately AES800.

BS21(R)C7 is a genetically broad-based synthetic cultivar developed after six cycles of reciprocal recurrent selection primarily for improved grain yield and root and stalk strength. It is an improved source of corn germplasm for use in areas of higher latitudes or in areas desiring earlier maturity.

BS22(R)C7 is a genetically broad-based synthetic cultivar developed after six cycles of reciprocal recurrent selection primarily for improved grain yield and root and stalk strength. It is an improved source of corn germplasm for use in areas of higher latitudes or in areas desiring earlier maturity.

A composite of annual teosinte and corn germplasm was used as a source of 2-eared inbred lines. The proportion of teosinte germplasm and the maize stocks are not known. Eight inbred lines with good agronomic performance in hybrid combinations were selected and recombined to give a synthetic designated as "Teozea". Teozea was further sib-mated with selection for 2-eared plants for 2 generations. An additional generation of random mating with no selection was used to obtain the seed supply for distribution as BS23. Evaluations have shown that this synthetic silks 3 to 4 days earlier than Iowa Stiff Stalk Synthetic (BSSSCO), has a high frequency of second ears when the plant density is 16,000 plants/acre or less, has a strong "stay-green" characteristic in Iowa, and yields well in crosses with BSSSCO.

BS26 was developed by intermating 50 selected S1 lines from "Lancaster Composite", followed by 3 generations of random mating. Lancaster Composite was developed by intermating 15 inbred lines that included C103 germplasm with 5 populations that included Lancaster Sure Crop germplasm. After 5 generations of intermating, S1 lines were developed and evaluated for pest resistance, maturity, and agronomic traits. Based on S1 performance, 400 were advanced to S2 generation and evaluated per se and in testcrosses with B73 x B84. Index selection was used to determine the 50 S1 lines intermated to form BS26. This improved population includes germplasm that should be useful in applied breeding programs.

BS27 is an adapted population of Anitgua Composite obtained originally from the International Maize and Wheat Improvement Center(CIMMYT) located near Mexico City. Antigua is a tropical variety that was adapted to temperate conditions by mass selection for earlier flowering. Mass selection was initiated in 1977 and after 6 cycles of selection Antigua Composite was considered to have maturity appropriate for U.S. Corn Belt environments. BS27 has a vigorous plant type, intermediate height, and ears with flinty kernels that are light yellow to light orange. BS27 has good combining ability with Corn Belt dent cultivars. BS27 includes germplasm that exhibits good pest resistance in tropical areas and includes germplasm that is different from that currently included in U.S. Corn Belt breeding programs. Maturity classification is AES800.

BS28 is an adapted population of Tuxpeno germplasm. Samples of five strains of Tuxpeno were obtained from CIMMYT, five samples were bulked, planted in isolation, and allowed to intermate to form Tuxpeno Composite. Mass selection was initiated in Tuxpeno Composite for earlier flowering in 1987. After six cycles of selection, the selected strain of Tuxpeno Composite was designated as BS28. BS28 includes germplasm that is considered one of the more important tropical races because of its good combining ability. BS28 could be used in breeding programs that want to include elite tropical germplasm adapted to temperate environments. Maturity classification is AES700-800.

BS29 is an adapted strain of Suwan-1, which was developed by Kasetsart University at Farm Suwan near Bangkok, Thailand. A sample of Suwan-1 [PI 439741-Suwan #1(S)C6] was obtained in 1986. Mass selection for earlier flowering was initiated in 1987. After six cycles of mass selection for adaptation, the population was designated as BS29. BS29 sheds pollen 9 days later than B73 x Mo17 and has 5.2% greater grain moisture at harvest. BS29 has excellent general combining ability with other adapted tropical varieties (BS16, BS27, and BS28). BS29 has good specific combining ability with BS10 and BSSS. BS29 has excellent grain quality; ears have flinty dark yellow kernels. BS29 is a strain of Suwan-1 adapted to temperate environments that should have potential in temperate breeding programs. Maturity classification is late AES800.

BS30 is a source of Iodent germplasm. Nineteen inbred lines that originated from the initial sampling of Iodent by M. T. Jenkins in 1922 were intermated to produce BS30. BS30 has a yellow, dent kernels on large girthed ears. Plant phenotypes are typically robust with large tassels, but plants generally have poor root and stalk strength. Maturity classification of BS30 is AES800.

Iowa Synthetic AA, designated BSAA, was developed by recombining 58 North Central Corn Belt lines. Recurrent selection based upon S1 line evaluation was used for 4 cycles to improve this synthetic for resistance to first generation European corn borer and resistance to stalk rot. In all cycles, evaluations of S1 lines were made in separate experiments under artificial infestations of the corn borer and artificial inoculations of Diplodia stalk rot. Whereas, the original BSAA was intermediate in resistance to both corn borer and stalk rot, BSAA(SRCB)C4 is resistant to both. Also, BSAA(SRCB)C4 is slightly earlier than BSAA for anthesis.

Iowa Synthetic BB, designated BSBB, was developed by recombining 44 North Central Corn Belt inbred lines. At least 12 of these lines have germplasm from Iowa Stiff Stalk Synthetic. Recurrent selection based on S1-line evaluation was used for 4 cycles to improve this synthetic for resistance to first-generation European corn borer and resistance to stalk rot. In all cycles, evaluations of S1 lines were made in separate experiments by using artificial infestations of the corn borer and artificial inoculations of Diplodia stalk rot. It is slightly later than BSBB for anthesis.

This improved breeding population was developed from 9 cycles of half-sib reciprocal recurrent selection, followed by 3 cycles of full-sib reciprocal recurrent selection. The tester population was BSSS(R)C11. BSCB1 was synthesized from 12 inbred lines: A340, CC5, Hy, I205, K230, L317, OhO7, Oh33, Oh4OB, Oh5lA, P8, and R4. Screening among and within S1 lines for first-generation European corn borer, Ostrinia nubilalis (Hubner), resistance and stalk-rot resistance was done in selecting elite material for the testcross trials.

This synthetic was developed from BSL(S)C4 with additional improvement for stalk quality. BSL(S)C4 was developed from the open- pollinated variety, Lancaster Surecrop, after 4 cycles of recurrent selection for stalk rot resistance. Three additional cycles of recurrent selection for resistance to mechanical breakage were used to obtain further improvement for stalk quality. BSL(S)C7 has better stalk-rot resistance than does BSL(S)C4, and it is much better than BSL(S)C4 for resistance to field stalk lodging.

This improved breeding population was developed from 9 cycles of half-sib reciprocal recurrent selection followed by 3 cycles of full-sib reciprocal recurrent selection with BSSS(R)C11 as tester. The tester population was BSCB1(R)C11. Screening among and within S1 lines for European corn borer, Ostrinia nubilalis (Hubner), resistance and stalk-rot resistance was done in selecting elite material for the testcross yield trials.

Developed to provide a population containing some exotic germplasm. One-fourth of the germplasm of this synthetic was derived from the Mexican race, Tuxpeno; and the other 3/4 was derived from the U.S. variety, Lancaster Surecrop. The population is an improved version of (Tuxpeno x Lancaster2) Synthetic. Five cycles of S2 recurrent selection for agronomic traits and yield have been completed; the population has improved grain yield and root and stalk quality relative to the original population.