Reciprocal Recurrent Selection Program Research Articles

<b>Response to the selection in the 11<sup>th</sup> cycle of reciprocal recurrent selection among full-sib families of maize</b> - doi: 10.4025/actasciagron.v35i4.17489

The continuous gains in cycles of recurrent selection have raised disagreement among researchers. Two hundred and forty-two full-sib families were obtained from CIMMYT and Piranao populations and evaluated in a simple lattice design in two environments to estimate the response to selection in the 11 th cycle of the UENF reciprocal recurrent selection program. No genotype x environment interaction was observed for most of the traits evaluated, indicating that a single recurrent selection program can be conducted for both sites. The population studied exhibited wide genotypic variability and heritability estimates ranged from 33 to 73%, indicating prospects of selection gain for the following cycles. The predicted genetic gain in yield was 12.90%. It is possible to conclude that the populations studied may be promising for the achievement of new selection cycles, which provides a continuous concentration of favorable alleles and the production of hybrids for the North and Northwest regions of the state of Rio de Janeiro.

Hybrid wheat: quantitative genetic parameters and consequences for the design of breeding programs

Commercial heterosis for grain yield is present in hybrid wheat but long-term competiveness of hybrid versus line breeding depends on the development of heterotic groups to improve hybrid prediction. Detailed knowledge of the amount of heterosis and quantitative genetic parameters are of paramount importance to assess the potential of hybrid breeding. Our objectives were to (1) examine the extent of midparent, better-parent and commercial heterosis in a vast population of 1,604 wheat (Triticum aestivum L.) hybrids and their parental elite inbred lines and (2) discuss the consequences of relevant quantitative parameters for the design of hybrid wheat breeding programs. Fifteen male lines were crossed in a factorial mating design with 120 female lines, resulting in 1,604 of the 1,800 potential single-cross hybrid combinations. The hybrids, their parents, and ten commercial wheat varieties were evaluated in multi-location field experiments for grain yield, plant height, heading time and susceptibility to frost, lodging, septoria tritici blotch, yellow rust, leaf rust, and powdery mildew at up to five locations. We observed that hybrids were superior to the mean of their parents for grain yield (10.7%) and susceptibility to frost (-7.2%), leaf rust (-8.4%) and septoria tritici blotch (-9.3%). Moreover, 69 hybrids significantly (P<0.05) outyielded the best commercial inbred line variety underlining the potential of hybrid wheat breeding. The estimated quantitative genetic parameters suggest that the establishment of reciprocal recurrent selection programs is pivotal for a successful long-term hybrid wheat breeding.

Molecular changes during intra and inter recurrent selection of two populations of maize: one adapted and one non adapted to the selection environment

In several reciprocal recurrent selection (RRS) programs heterosis and favorable characteristics are achieved by means of one adapted and one non adapted population. We evaluated with molecular markers, an intrapopulation selection followed by RRS of one Spanish population adapted to Mediterranean Spain and one US Corn Belt population non adapted to Spanish conditions. Results from other authors suggest that during recurrent selection, non adapted populations have higher loss of variability, genetic differentiation and lower effective population size than expected according to the number of families selected each generation. This could be due to natural selection which is not under the breeder’s control and is expected to mainly act on non adapted populations. The number of markers with convergent allelic change was similar to the number of markers with divergent allelic change which explains the lack of genetic differentiation and the failure to increase heterosis during RRS because the effects of both types of changes compensate. It seems that the predominant mode of gene action depends on the particular germplasm involved in the RRS. By evaluating the allelic changes during selection, we identified four regions (2.04, 4.06, 6.03, 9.02) that significantly changed during selection in our selection experiment and that have been associated to selection in other selection experiments and to multiple traits in QTL experiments.

An initial assessment of linkage disequilibrium (LD) in coffee trees: LD patterns in groups of Coffea canephora Pierre using microsatellite analysis

BackgroundA reciprocal recurrent selection program has been under way for the Coffea canephora coffee tree for approximately thirty years in the Ivory Coast. Association genetics would help to speed up this program by more rapidly selecting zones of interest in the genome. However, prior to any such studies, the linkage disequilibrium (LD) needs to be assessed between the markers on the genome. These data are essential for guiding association studies.ResultsThis article describes the first results of an LD assessment in a coffee tree species. Guinean and Congolese breeding populations of C. canephora have been used for this work, with the goal of identifying ways of using these populations in association genetics. We identified changes in the LD along the genome within the different C. canephora diversity groups. In the different diversity groups studied, the LD was variable. Some diversity groups displayed disequilibria over long distances (up to 25 cM), whereas others had disequilibria not exceeding 1 cM. We also discovered a fine structure within the Guinean group.ConclusionsGiven these results, association studies can be used within the species C. canephora. The coffee recurrent selection scheme being implemented in the Ivory Coast can thus be optimized. Lastly, our results could be used to improve C. arabica because one of its parents is closely related to C. canephora.

Meiotic stability in two valuable interspecific hybrids of Brachiaria (Poaceae)

With 2 figures and 2 tablesAbstractIn an attempt to increase genetic variability in the genus Brachiaria, crosses were made between sexual tetraploidized accessions of B. ruziziensis and apomictic tetraploid accessions of B. brizantha (2n = 4x = 36). Among the F1 progenies, two hybrids (Hb331, apomictic; and Hb336, sexual) displayed several agronomically desirable traits. These hybrids were evaluated for several years, and the apomictic one is now being tested under grazing to be released as a new cultivar, whereas the sexual one is in a reciprocal recurrent selection programme. The possibility of gene exchange through recombination of genitors and their meiotic behaviour was investigated. Both hybrids were evaluated for meiotic stability during three consecutive years. Analyses of meiocytes at diakinesis revealed multivalent chromosome associations among the parental genomes, indicating that their gene pools are interchangeable. Irregular chromosome segregation, chromosome stickiness and a putative meiotic mutation were recorded. The frequency of abnormalities varied among years and also between the hybrids. The sexual hybrid Hb336 had a more stable meiotic behaviour, but pollen fertility was higher in apomictic Hb331, ensuring more viable seed formation.

Comparison of two methods of reciprocal recurrent selection in maize (Zea mays L.)

Reciprocal recurrent selection (RRS) was proposed for simultaneously improving two populations and their cross. A modification of the classical full-sib RRS (FS-RRS) was proposed in which the performance of full-sibs and S(2) families is combined in a selection index (FS-S(2)-RRS). The Mediterranean corn borer (MCB) is the main corn borer species in the Mediterranean and adjacent areas and produces important yield losses. We started two RRS programs (FS-RRS and FS-S(2)-RRS) from the same maize population in which the selection criterion was grain yield under artificial infestation with MCB eggs. Original populations, two cycles of selection derived from them by both RRS methods, and population crosses were evaluated under MCB attack and under insecticide treatment in three different environments. The objective was to compare the efficiency of the FS-RRS and the FS-S(2)-RRS methods for improving grain yield. We found that the FS-S(2)-RRS method was successful for improving the yield of the population cross under optimum conditions (the regression coefficient over cycles was b = 0.87** Mg ha(-1) cycle(-1)) without losing yield under high pressure of MCB attack (b = 0.07). On the contrary, FS-RRS failed to improve the yield of the population cross under optimum conditions (b = 0.65) and tended to decrease the yield under high levels of MCB attack (b = -0.26). We conclude that for developing high yielding and stable varieties, FS-S(2)-RRS is more efficient than the classical FS-RRS method.

Full-sib reciprocal recurrent selection in the maize populations Cimmyt and Piranão

We estimated the genetic gains of the 12th cycle of reciprocal recurrent selection for maize traits of agronomic interest. We used 23 ISSR molecular markers in an attempt to maximize genetic variability among and within populations based on selection of S(1) progenies. To this end, 138 full-sib families were evaluated in a randomized block design in two environments (the municipalities of Campos dos Goytacazes and Itaocara, in the State of Rio de Janeiro, Brazil), with replications within sets. Direct selection for grain yield was used for the selection of the families. To assess genetic diversity among and within populations, we examined plants produced from part of the S(1s) seeds from the parents that originated the 42 full-sib families that were selected from the agronomic traits. Direct selection for grain yield provided good gains for the traits evaluated, with estimated improvement of -0.87 days for days to flowering, 0.35 plants, 1.79 ears per plot, 0.58 g per 100-grain weight, 308.21 g ear weight per plot, and 261.83 kg/ha grain yield. Application of molecular markers at the stage of superior progeny selection led to increased genetic distance among populations, which is a very important factor for utilization of heterosis and providing greater longevity to the reciprocal recurrent selection program.

Three Cycles of Full‐Sib Reciprocal Recurrent Selection in Two Spanish Maize Populations

ABSTRACTSpanish maize (Zea mays L.) populations can be useful for enhancing adaptation and stress tolerance of commercial varieties. Two improved Spanish maize populations, one from the northwest and the other from the southeast of Spain, that represent an alternative heterotic pattern have been subjected to three cycles of full‐sib reciprocal recurrent selection to increase the performance of the population cross. The objectives of this study were to evaluate the effect of selection on grain yield and on the correlated responses in the populations and their crosses and to investigate changes in heterosis and inbreeding depression during selection. Ten populations per se (S0), selfed (S1), and intercrossed were evaluated at six environments. Yield significantly increased with selection in the population cross (4.1% per cycle) and in the northwestern population (6.7% per cycle). Yield of the southeastern population did not change with selection. Correlated responses in other important agronomic traits were also in the desired direction. Mid‐parent and high‐parent heterosis increased significantly with selection (2 and 1.5%, respectively). The third cycle of selection of both populations is an interesting source for new inbred lines that could be the foundation for new adapted hybrids. The cross between the improved cycles could be useful for sustainable or organic agriculture as population hybrids, but more importantly, the reciprocal recurrent selection program can continue improving the population cross.

Use of molecular markers in reciprocal recurrent selection of maize increases heterosis effects

We examined the effect of incorporation of molecular markers on variability between and within populations in order to maximize heterotic effects and longevity of a maize reciprocal recurrent selection program. Molecular variability was quantified by inter-simple sequence repeat (ISSR) markers between and within the maize populations Cimmyt and Piranão in the 10th cycle of a reciprocal recurrent selection program. Forty-two S(1) progenies of each population were analyzed, these being families of full-sibs selected according to their agronomic traits. Thirteen primers were selected, which produced 140 bands; 114 of them were polymorphic and 26 monomorphic. Based on UPGMA grouping analysis and by genetic distances, it was possible to identify "contaminant" progenies. These progenies belong to the Piranão or Cimmyt groups, but cluster in the opposite heterotic group. Identification of "contaminant" progenies is relevant for selection, because, besides identifying genotypes that should be eliminated at the recombination stage, it allows increased heterosis expression in crosses between more genetically distinct individuals. After the elimination of the "contaminant" progenies and those that were allocated between the heterotic groups, a new statistical analysis was carried out, which demonstrated increased genetic distances between the populations. It was concluded that the application of molecular markers in reciprocal recurrent selection programs allows the optimization of the monitoring of genetic variability within and between populations, favoring recombination between more distant progenies, besides ensuring increased longevity of the reciprocal recurrent selection program.

Recurrent selection of cocoa populations in Côte d’Ivoire: comparative genetic diversity between the first and second cycles

AbstractIn Côte d’Ivoire, the cocoa breeding programme has been based on the creation of hybrids between different genetic groups. From 1990 onward, a reciprocal recurrent selection programme has been set up with the purpose of improving simultaneously the characteristics of the two main genetic groups: Upper Amazon Forastero (UA) and a mixture of Lower Amazon Forastero (LA) and Trinitario (T). Based on data obtained from 12 microsatellite primers, the genetic diversity and genetic distances of the parental populations used in the first and second selection cycles are presented. The results revealed that the diversity of populations UA0 and UA1 on the one hand and (LA+T)0 and (LA+T)1 on the other is similar. The genetic distances were small between the parental populations used for the first and second cycles. Genetic diversity was greater in the UA group than in the LA+T group. The number of rare and of private alleles was reduced for both genetic groups, as well as the number of the frequent alleles in the LA+T group.

Seleção recorrente recíproca na obtenção de híbridos interpopulacionais de milho-pipoca

O objetivo deste trabalho foi avaliar a eficiência da seleção recorrente recíproca em produzir híbridos de milho-pipoca (Zea mays) de progênies endógamas superiores, com famílias de irmãos-completos. O programa de seleção recorrente recíproca envolveu as populações de milho-pipoca 'Viçosa' e 'Beija-Flor'. Os testes dos híbridos S0xS0 e S1xS1 foram conduzidos em delineamento látice, nos anos agrícolas de 2002/2003 e 2004/2005. Os dois ensaios incluíram testemunhas comerciais comuns, que permitiram a comparação do desempenho dos híbridos. Analisaram-se a produtividade e a capacidade de expansão. Foram preditos ganhos direto e indireto com a seleção em capacidadede expansão, avaliada em pipoqueira de ar quente e na pipocadora "Metric Weight Volume Tester". Os ganhos observados foram calculados para avaliar a eficiência da seleção recorrente recíproca. As análises de covariância mostraram variabilidade genotípica nas populações. Em relação às testemunhas comerciais, os híbridos S0xS0 foram inferiores em qualidade e equivalentes em produtividade, e os híbridos S1xS1 foram equivalentes nas duas características. O ganho observado na capacidade de expansão foi substancial, cerca de 4 mL g-1, superior ao ganho predito (2,8 mL g-1). A redução observada na produtividade não foi relevante. Verificou-se redução na variabilidade genotípica quanto à capacidade de expansão. O método de seleção recorrente recíproca foi eficiente em produzir híbridos S1xS1 superiores aos S0xS0.

Análise dialélica da capacidade combinatória de variedades de milho-pipoca

Seis variedades de milho pipoca (Amarela, Roxa, Branca, Rosa-claro, Beija-flor e Viçosa), Zea mays L. (Poaceae), seus 15 híbridos F1’s e 15 híbridos F1’s recíprocos foram avaliados em um delineamento em blocos ao acaso, com três repetições, instalado em Viçosa, nos anos agrícolas 90/91 e 91/92, e Visconde do Rio Branco, em 91/92. Avaliaram-se os seguintes caracteres: altura da planta, altura da espiga, peso de grãos e capacidade de expansão. A variedade Viçosa foi indicada para ser usada em híbridos ou como fonte de linhagens para uso em programas de melhoramento intra ou interpopulacionais. O híbrido Viçosa x Roxa mostrou-se o mais desejável considerando rendimento e capacidade de expansão. As combinações Viçosa com Roxa e Rosa-claro com Beija-flor foram indicadas para iniciar programa de seleção recorrente recíproca, uma vez que foram as que mais se complementaram em relação ao peso de grãos e capacidade de expansão. Nestes programas, atenção especial deve ser dada à capacidade de expansão, que é a característica mais limitante nestes híbridos. Apesar de haver evidência de efeitos recíprocos para todos os caracteres, verificou-se pouca importância dos mesmos

Population Genetic Diversity in a Maize Reciprocal Recurrent Selection Program

The genetic structures of the Iowa Corn Borer Synthetic #1 (CB) and Iowa Stiff Stalk Synthetic (SS) maize (Zea mays L.) populations are important because these populations serve as the model for development of modern commercial hybrids. In 1949, CB and SS were used to start a reciprocal recurrent selection (RRS) breeding program at Iowa State University. This study was conducted to analyze more thoroughly the genetic diversity within this RRS program and illustrate how the RRS program has changed over time at the molecular level. The progress of this program was measured by analyzing the variation at 86 SSR loci among 28 progenitor lines and 30 plants sampled from each of seven cycles (Cycle 0, Cycle 1, Cycle 3, Cycle 6, Cycle 9, Cycle 12, and Cycle 15) in each population. The progenitors of these populations show a high amount of variation on the basis of expected heterozygosity (0.557). As the RRS program proceeded, this variation decreased (Cycle 15, 0.245). In total, a larger amount of genetic variation was found among plants within cycles (66%) than among cycles (13%) or between populations (21%). The repartitioning of variation from within populations (96% in progenitors) to between populations (58% in Cycle 15) over time is consistent with theoretical expectations of divergence between the populations. By sampling intermediate time points, we gained a comprehensive genetic view of CB and SS permitting evaluation of the molecular‐level changes occurring as a result of reciprocal recurrent selection.

Molecular Genetic Diversity among Progenitors and Derived Elite Lines of BSSS and BSCB1 Maize Populations

The maize (Zea mays L.) populations Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic No. 1 (BSCB1) have undergone reciprocal recurrent selection (RRS) since their establishment in 1949. This study focused on molecular genetic variation of the progenitor inbred lines used to synthesize BSSS and BSCB1 as well as elite inbred lines derived from different cycles of selection. Our objectives were to investigate changes in allele frequencies and genetic diversity from progenitors to derived lines and evaluate trends in genetic diversity among elite lines derived from early and advanced selection cycles. Genotypic data for 105 restriction fragment length polymorphism (RFLP) loci were collected from four groups: 16 progenitors and 18 elite lines derived from BSSS, 12 progenitors and 7 elite lines derived from BSCB1. Each progenitor group had a broad genetic base but both were genetically similar. The groups of derived lines diverged substantially from each other. A larger Roger's distance was found between the groups of lines derived from advanced cycles than between the groups of lines derived from Cycle 0. Allelic variation within each group of lines, however, decreased just slightly with the elite lines capturing almost 75 and 67% of the allelic variation present in the progenitor lines of BSSS and BSCB1, respectively. The results of this study confirm the long-term potential of this RRS program and the importance of the choice of broadly based progenitor materials.

Molecular Genetic Diversity among Progenitors and Derived Elite Lines of BSSS and BSCB1 Maize Populations

The maize (Zea mays L.) populations Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic No. 1 (BSCB1) have undergone reciprocal recurrent selection (RRS) since their establishment in 1949. This study focused on molecular genetic variation of the progenitor inbred lines used to synthesize BSSS and BSCB1 as well as elite inbred lines derived from different cycles of selection. Our objectives were to investigate changes in allele frequencies and genetic diversity from progenitors to derived lines and evaluate trends in genetic diversity among elite lines derived from early and advanced selection cycles. Genotypic data for 105 restriction fragment length polymorphism (RFLP) loci were collected from four groups: 16 progenitors and 18 elite lines derived from BSSS, 12 progenitors and 7 elite lines derived from BSCB1. Each progenitor group had a broad genetic base but both were genetically similar. The groups of derived lines diverged substantially from each other. A larger Roger's distance was found between the groups of lines derived from advanced cycles than between the groups of lines derived from Cycle 0. Allelic variation within each group of lines, however, decreased just slightly with the elite lines capturing almost 75 and 67% of the allelic variation present in the progenitor lines of BSSS and BSCB1, respectively. The results of this study confirm the long-term potential of this RRS program and the importance of the choice of broadly based progenitor materials.

Análise dialélica e heterose de populações de milho-pipoca

Realizaram-se cruzamentos dialélicos entre nove populações de milho-pipoca (Zea mays L.) - UNB-2, RS-20, UEM-J1, UEM-M2, CMS-42, CMS-43, Viçosa, Beija-flor e a geração avançada do híbrido triplo Zélia - para a obtenção dos 36 híbridos F1's a fim de alcançar informação dos valores da capacidade combinatória e heterose. Essas populações e os F1's foram avaliados em ensaios, em dois anos agrícolas (98/99 e 99/00), em Iguatemi (PR), com três repetições por ano. Os resultados permitiram recomendar compostos formados entre as populações de alta capacidade geral de combinação (CGC) para rendimento de grãos, UNB-2 e CMS-42 e as populações de alta CGC para capacidade de expansão, Zélia, RS-20 e UEM-M2. As populações Beija-flor e RS-20 foram recomendadas para iniciar programa de seleção recorrente recíproca, pois se complementam em relação ao rendimento de grãos e à capacidade de expansão (CE). Para CE, houve heteroses positiva e negativa, verificando-se dominância não unidirecional.

Heterosis and its components in crosses among high quality protein maize populations

The objective of the present study was to investigate heterosis in high quality protein maize populations of distinct grain type groups. Agronomic traits and reaction to some leaf diseases of 19 yellow grain populations were assessed in a partial diallel grown in four environments. For grain yield trait, only variety effects and average heterosis were significant, indicating that the best intervarietal hybrids can be predicted using the means of the parental populations. The BR 473 and CMS 52 flint populations, the CMS 474 and ZQP 103 dent populations are recommended for an inter-group reciprocal recurrent selection program. In a decreasing order of preference, the dent type CMS 474, ZQP 103 and ZQP 101 populations and the flint type BR 473, CMS 455C, CMS 453, CMS 52, CMS 455 and CMS 458 are recommended to form composites.

Analysis of Diallel Cross for the Evaluation of Maize Populations Across Environments

Eleven open-pollinated maize (Zea mays L.) populations were crossed in a diallel scheme and evaluated in five locations in the State of Parana: [1] Ponta Grossa, [2] Pato Branco, [3] Palotina, [4] Londrina and [5] Guarapuava. Two commercial hybrids (P 3230 and BR 201) were included as checks in the experiments, thus completing 68 entries (11 parents, 55 hybrids and 2 checks). Plots were represented by single rows 5 m long spaced 0.9m with 25 plants per plot after thinning. The following traits were analyzed: GY- total plot grain yield expressed in kg/ha after adjustment to 14.5% grain moisture; PH- plant height (cm); EH- ear height (cm); and FF- days for female flowering. Plant height and EH were not included in location [2]; FF was not include in locations [2] and [3]. The joint analysis of variance showed significance for all traits, only for the variation among location, entries, variety effects and average heterosis. For yield the total heterosis in mid-parent percentage varied from –0.96% (PMI 8403 x PMI 9304) to 32.4% (PMI 9302 x PMI 9307). Variety effects (v i ) and general combining ability (g i ) effects were in the range of –1483 to 772 kg/ha and from –847 to 448 kg/ha, respectively. Both g i (for yield) and v i (for the other traits) were used to select two populations to be used in a reciprocal recurrent selection program. BR 106 showed the highest estimates for both g i and v i for yield but also showed undesirable traits (tall plants and late flowering). Some outstanding populations for yield potential per se did not show a good performance in crosses. Other populations with outstanding performance in crosses exhibited lower variety effects for yield or high variety effects for the other traits. Some introduced populations who showed shorter plants and earliness should be submitted to selection for yield, adaptation and other agronomic traits before being indicated for crossing. However, they should be recommended as source populations for short architecture and early flowering. An overall analysis led to the decision of choosing the population IAPAR 26 to be used as contrasting parent of BR 106 in a reciprocal recurrent selection program at IAPAR (Londrina, State of Parana).

Analysis of the genetic effects for several traits in oil palm (Elaeis guineensis Jacq.) populations. I. Population means

An oil palm experiment was set up in the Ivory Coast to compare the effects of crossing and selfing within two origins, Deli and La Mé, on the mean and the variability of Deli x Mé between-origin hybrids. The originality of the experiment lay in the crossing plan, which provided access to genetic parameters related to additivity, dominance and different components of epistasis. This first part covers the analysis of the components of the mean. The parents used were obtained from four palms, two from each origin. Those of La Mé origin were half-sibs. The common parent came from a wild stand in the Ivory Coast. Those of Deli origin were from two different populations bred in Southeast Asia for several generations from a narrow genetic base. These four parents gave rise to nine Deli x La Mé hybrid populations with double-cousintype links. The additive component is more important within the Deli origin than within the La Mé origin. This may be explained by the large genetic divergence between the two Deli parent palms. On the other hand, the additive(*) additive epistasis is more substantial within the La Mé origin, probably because of inbreeding. The discussion concentrates on how this information should be used when choosing parents to be crossed and tested and to produce improved populations. The crossing plan proposed can be of general use and is suitable for other species in a reciprocal recurrent selection programme.

Change in ribosomal DNA intergenic spacer-length composition in maize recurrent selection populations. 1. Analysis of BS13, BSSS, and BSCB1

Five different ribosomal DNA (rDNA) intergenic spacer-length variants (slvs) were detected among the maize inbreds which were the progenitors of Iowa Stiff Stalk Synthetic (BSSS). One rDNASstI restriction site polymorphism in the 3' region of the 26S gene was detected. Nine different rDNA intergenic spacer (IGS) hybridization fragment patterns (assigned letter designations A-I) were observed among the BSSS progenitors. Following 7 cycles of half-sib recurrent selection in BSSS using the Ia13 double cross as a tester, hybridization fragment pattern E became predominant in the population. In contrast, 11 cycles of reciprocal recurrent selection in BSSS with the Iowa Corn Borer Synthetic No. 1 (BSCB1) population resulted in hybridization pattern D becoming predominant. Hybridization pattern E is present in the elite inbreds B14, B37, B73, and B84, which were derived from different cycles of the BSSS half-sib recurrent selection program with Ia13. Hybridization pattern D is present in the elite inbreds B89 and B94, which were derived from different cycles of the BSSS reciprocal recurrent selection program with BSCB1. Therefore, two different forms of recurrent selection on BSSS resulted in different hybridization patterns becoming predominant in the selected populations and present in elite inbreds derived from the populations. These results also suggest that rDNA IGS hybridization fragment patterns D and E, which both have the longest slv detected, may have a selective or adaptive advantage in BSSS materials grown in the Corn Belt.