Recurrent Selection Methods Research Articles

Genetic Drift and Selection Evaluated From Recurrent Selection Programs in Maize

If recurrent selection methods are effective, the frequency of favorable alleles is expected to increase in the population. Random changes in gene frequency will also occur, if effective population size is small, due to the effect of sampling. In maize (Zea mays L.), where dominance gene action is positive in direction for traits such as grain yield, genetic drift results in inbreeding depression. Genetic drift is the change in gene frequency due to sampling in a finite population. Two major processes are expected to be operating to change the mean over cycles of recurrent selection in a population of finite size, selection acting to increase the mean and inbreeding depression due to genetic drift acting to decrease the mean. Estimation of the effects of genetic drift may be useful because the choice of what constitutes adequate effective population size may be altered, on the basis of empirical results. The objectives of the current study were to compare progress between reciprocal recurrent selection (RRS) and intrapopulation selection that included half‐sib (HT) and S2 (S) selection in ‘Iowa Stiff Salk Synthetic’ (BSSSC0), and to separate the effects of selection from those of genetic drift. Effects due to selection for grain yield improvement of populations on a per‐cycle basis were not significantly different between methods of recurrent selection. When advanced cycles were evaluated for grain yield in crosses with an unrelated inbred line (Mo17), improvements paralleled improvement in the populations. The improved populations crossed to an unrelated population [BSCB1(R)Cn], which was used reciprocally as the tester for BSSS(R)Cn, suggested that response to RRS in improving the population cross mean was similar to the populations improved by either HT or S methods of selection. Effects of genetic drift were significant and should be considered in long‐term selection programs. Differences among selection methods for genetic drift were not significant.

Optimization of recurrent selection on the phenotypic value of doubled haploid lines

Three methods of recurrent selection using doubled haploids (DH) are compared with the same resources: individual line selection (with one DH line per plant), selection between and within families, and selection index of family and line within family values. It seems that for low heritabilities at the individual level, the selection index method is the most efficient method, followed by the selection between and within families. Because of the difficulty in optimizing selection intensities, the selection between and within families can be less efficient than individual line selection. For very low heritabilities, it will be better to use selection index with a relatively low number of lines per haploidized plant, to minimize the rate of decrease of the effective population size. For a large range of situations, recurrent selection with only one DH line per plant seems one of the more efficient and the simpler methods.

Microcomputer Simulation of Expected Gains from Eight Methods of Intrapopulation Recurrent Selection

AbstractAn interactive microcomputer program was developed to provide plant breeders and graduate students in quantitative genetics the opportunity to devise selection strategies and review expected gains for eight intrapopulation selection methods. Selection methods include uniparental and biparental mass selection, three forms of half‐sib selection, full‐sib selection, and S1 and S2 selection. Users provide estimates of genetic and environmental components of variance, selection intensities, and an array of possible experimental designs including number of environments, number of replicates within environments, and plot size. Expected gains can be expressed as either gain cycle−1, gain year−1, or gain season−1. Help screens are included that explain selection methods and the calculation of expected gains. The program is designed so the user can easily move within it, reenter values for individual variables, and rapidly redisplay results.

Plant breeding methodology

Part 1 Introductory topics: introduction to methodology genetic engineering and the future. Part 2 Breeding and selection methods: primary methods shaped by historical usage - a preamble the mass selection method pedigree and f+d2-derived family methods backcross method methods shaped by competitive forces the multiblend variety the multiline method methods shaped by recurrent forces the recurrent selection method diallel selective mating method genetic male sterility male sterile facilitated recurrent selection method methods shaped by requirements of techniques heterosis and commercial hybrids the single seed descent method doubled haploid method. Part 3 Breeding and selection strategies: issues in selection - a preamble visual selection selection indices harvest index stability. Part 4 Germ plasm and crossing considerations: germ plasm choosing cross quality level predicting and choosing parents predicting and choosing crosses and lines hybridizing or crossing techniques. Part 5 Plant traits of special relevance: seed characteristics morphological and other traits. Part 6 Project management: the four stages of plant breeding minimum staff plant breeding choosing sites and environments field organization and operations 101 ways to enrich your breeding program.

Effects of Recurrent Selection in Corn Populations

Recurrent selection methods were conducted in corn (Zea mays L.) populations to increase the frequency of favorable alleles for grain yield. Populations under recurrent selection were evaluated to estimate response to selection and to compare the relative effectiveness of the different methods of recurrent selection for grain yield improvement. Ten populations, their improved strains, and the S1 generation of the original and improved strains were evaluated in four field environments. This study was conducted to estimate the direct and indirect responses to selection of the 10 populations and their respective S1 generations for different methods of selection. Positive response to selection for greater grain yield was realized for each selection method except for one population (BSCB1) undergoing reciprocal recurrent selection. Average response (0.249 Mg ha−1 cycle−1) for the intrapopulation selection methods was greater than the average response (0.033 Mg ha−1 cycle−1) for the interpopulation selection methods. Response in the S1 generations was similar to the response of the noninbred populations. Reduction in inbreeding depression averaged 12%. The S1 generations of two selected populations [BS13(S)C4 and BS12(HI)C7] had significantly greater yields than the nonselected, noninbred populations from which the selected populations were derived. Positive response to selection was accomplished without selection for taller, later‐maturity genotypes. No consistent trends were detected for changes in root and stalk lodging with selection for grain yield.

Comparison of S1 and Modified Ear‐to‐Row Recurrent Selection in Four Maize Populations. I. Effects on Population Means and Variances1

Concern for the narrow genetic base of modern maize (Zea mays L.) hybrids has resulted in an increased interest in a population approach to germplasm improvement and the most effective recurrent selection methods for the adaptation and improvement of such populations. Two widely used procedures for intrapopulation improvement in maize are S1 (S) and modified ear‐to‐row (ME) selection. The objective of this study was to compare the effectiveness of these two procedures in four open‐pollinated maize populations, Afton (A), Schindelmeiser (S), Gelber Badischer Landmais (G), and Northwestern Dent (N). The primary trait of selection was performance index (PI = grain yield/percent grain moisture). The effects of selection were assessed for PI, the components of PI: grain yield and percent ear moisture at harvest, and other agronomic traits. Genetic variance was estimated to determine possible relationship to observed progress from selection. Data are reported for the initial three cycles of each selection procedure. The S selection for PI resulted in significant average linear increases in PI of 13, 12, and 19% per cycle in A, G, and N, respectively. Increases in PI were a result of increases in grain yield and decreases in percent moisture at harvest. ME selection produced no significant changes in PI. Genetic variances were estimated by subtracting environmental variance (as estimated from single‐cross hybrids) from the phenotypic variance of each cycle. Significant reductions in genetic variances from Cycle 0 were detected for grain yield in (S)Cycle 3 of S, G, and N, and were numerically lower in all selected populations. Genetic variances for percent ear moisture declined significantly in only two instances, ^(ME)Cycle 3 and G(S)Cycle 3. This study indicated that S selection was the preferred method of intrapopulation improvement compared to ME selection.

A RECURRENT SELECTION SCHEME FOR FABA BEAN

A recurrent selection method for use in faba bean (Vicia faba) was evaluated over a 10-yr period. The method consists of growing superior lines in open-pollinated random mating nurseries (RMN), selecting heavily podded plants from these lines, evaluating the offspring for yield and seed protein concentration, and replacing inferior lines in the RMN with selections deemed superior. Two types of RMN were established, one for yield (RMY) and the other for both yield and seed protein content (RMP). The criterion for entry of a line into the RMY was a seed yield in the top 3 % of a yield trial while entry into the RMP required a line to be in the top 5% for seed yield and 3% for protein content. A positive increase in seed yield of the selected lines from both RMNs was found over time, but no increase in seed protein content was noted.Key words: Vicia faba, recurrent selection, breeding method, faba bean

Selection‐Induced Differences among Strains of Iowa Stiff Stalks Synthetic Maize1

Different recurrent selection methods have been used for the improvement of traits in maize (Zea mays L.). The relative performance of nine strains of Iowa Stiff Stalk Synthetic (BSSSCO) derived different methods of recurrent selection for different traits were determined by evaluating strains per se, diallel crosses among strains, and Sl generations of strains and strain crosses. Objectives were to determine selection. induced differences among the nine strains and the direct and indirect effects of selection for yield, grain moisture, root and stalk lodging, and dropped ears. Replicated field trials were conducted in six environments. BS13(S)C2 had the highest yield per se (7.83 Mg ha‐1) and the highest yielding $1 generation (5.82 Mg ha‐1). Inbreeding depression for yield was less for the highly selected strains and for crosses involving those strains. Selection for resistance to European corn borer (Ostrinia nubilalis Hübner) did not significantly affect yield, but selection for resistance to corn rootworm (Diabrotica virgifera Le Conte) did have a significant negative correlated effect on grain yield. Changes in frequency of additive effects due to selection for yield improvement were more important for BSI3(S)C2 (seven cycles half‐sib and two cycles S2 selection) than for BSSS(R)C8 (eight cycles reciprocal recurrent selection). Greater changes were observed in frequency of alleles with dominance effects in BSSS(R)C8 than in BS13(S)C2. After removal the effects of drift, rate of realized gain per cycle was 0.279 Mg ha‐1 (4.4%) for BS13(S)C2 and 0.259 Mg ha‐1 (4.1%) for BSSS(R)C8. Yield of the 36 strain crosses ranged from 6.10 Mg ha‐1 for BSSSCO ✕ BSSS(RW)C2 to 9.37 Mg ha‐1 for BSSS(R)C8 ✕ BS13(S)C2. Average midparent heterosis for yield was 11.7%. Yield differences among strains and level of heterosis expressed in crosses suggested selection‐induced genetic diversity among strains of BSSSCO.

Choice of environments in reciprocal recurrent selection programs

An alternative method of reciprocal recurrent selection (RRS) in which populations A and B are each evaluated in a different environment is proposed. This method is called dual-environment reciprocal recurrent selection (DERRS). Two genetic models are considered in the theoretical study. A comparison of selection methods shows that genetic gain is larger in DERRS than in RRS for the two models. The difference grows greater as the dominance effects operating in the two environments are more divergent and as the number of selection cycles increases. A greater gain is obtained when the genetic covariances between crosses in the two chosen environments are lower.

Compendium of recurrent selection methods and their application

Recurrent selection is a breeding method that has been used for the genetic improvement of germplasm. Although recurrent selection methods were suggested over 40 years ago, there use has not been as extensive as the other classical plant breeding methods. Recurrent selection is used for the improvement of traits inherited in a quantitative manner, and the primary objective of the method is to gradually increase the frequency of favorable alíeles and maintain genetic variability for future selection. Different methods of recurrent selection have been suggested, depending on the types of gene action considered important in the inheritance of the traits under selection, relative efficiency of selection, and the complexity of the trait under selection. Most methods of recurrent selection include three phases conducted in a repetitive manner; development of progenies, evaluation of progenies in replicated trials, and recombination of the superior progenies based on the evaluation trials. Most information suggests that the recurrent selection methods are effective for the improvement of the traits under selection, but in most instances the recurrent selection methods have not been integrated with other breeding methods for the development of new cultivars. Recurrent selection methods will be most effective when they are integrated with the applied aspects of plant breeding.

Reciprocal Full‐Sib Selection in Maize1

Reciprocal full‐sib selection was initiated in BS10 and BS11 maize (Zea mays L.) populations to emphasize selection for specific combining ability. Grain yield was the primary trait under selection, but consideration also was given to maturity and lodging resistance. Selection was based on performance of full‐sib progenies, and S1 progenies of the parents of the superior full‐sib progenies were intermated to synthesize the next cycle population. The original populations and their population cross, and the most advanced cycle populations and their crosses, also were included in most evaluation trials to provide information on relative response to selection. The primary objective of this paper is to summarize results of seven cycles of reciprocal full‐sib selection in BS10 and BS11. Direct response in the population cross was 2.1% per cycle for yield. Correlated response in BS10 and BS11 was 2.7 and 2.4%, respectively. Gradual improvement was realized in BS10 and the population cross, but most of the improvement in BS11 was made in the first cycle of selection. Relative to the mean of the six check hybrids included in all trials, the mean yield of the full‐sib progenies increased six standard deviations. There was no evidence that the variability among full‐sib progenies had decreased with seven cycles of reciprocal full‐sib selection. Evidence suggested that maturity was not later in advanced cycles and that stalk quality was improved. Percentage of root lodging and dropped ears did not show any trend with selection. Direct and correlated responses of reciprocal full‐sib selection in BS10 and BS11 were similar to those reported for other recurrent selection methods in other populations. Reciprocal full‐sib selection is somewhat more complex than other methods of recurrent selection, but it seems useful in certain situations where desired to select for general and specific combining ability.

Effects of Nitrogen Fertilization and Recurrent Selection on Performance of Hybrid Populations of Corn1

AbstractImproved corn (Zea mays L.) hybrids are generally developed at relatively high N fertility levels. Previous studies have shown that hybrid populations developed by different selection methods vary in their responsiveness to environments. Because N supply is an important factor of the environment which affects yield a field study was conducted to determine the N response of population hybrids improved by intra (full‐sib family) and inter (reciprocal recurrent) selection methods. The responses of the original population hybrid and the two improved population hybrids to N rates of 56, 168, and 280 kg N/ha were studied on an Aquic Paleudult.The improved populations produced more total dry matter and grain at each N level than did the original hybrid. This was associated with an increase in the ear number per plant as the N rate increased. The N concentration of the improved population hybrids at silking was correlated with ear number per plant. Average N use efficiency (grain per unit of N applied) for the improved population hybrids was greater than for the original hybrid. The higher yield of the reciprocal recurrent selection at 56 and 168 kg N/ha as compared with the full‐sib family selection was associated with a higher average N uptake efficiency.

Breeding for Rust Resistance in Orchardgrass by Phenotypic and Phenotypic‐Genotypic Selection1

Effectiveness of alternative selection methods is an important consideration in any plant breeding program. The purpose of this research was to evaluate recurrent phenotypic selection and selection based on both phenotypic performance and a polycross progeny test (phenotypic‐genotypic method) for resistance to rust (Puccinia graminis Pers.) in ‘Sterling’ orchardgrass (Dactylis glomerata L.). Rust resistance was improved by each of three cycles of phenotypic selection. One cycle of phenotypic‐genotypic selection (Cl‐PG) achieved the same level of rust resistance and required the same length of time as did two cycles of phenotypic selection (C2‐P). The mean rust rating of C1‐PG and C2‐P did not change with advancement from the first to the second generation; however, plant to plant phenotypic variation increased. Smaller phenotypic variances in both generations of C1‐PG and C2‐P than in Sterling suggested a decrease in genetic variance with selection; however, significant genetic variation was found in all derived populations. High parent clone‐topcross progeny correlations indicated that progeny testing for rust resistance is unnecessary. The recurrent phenotypic selection method would favor maintenance of greater genetic diversity for resistance than the phenotypic‐genotypic method because more plants could be selected in each cycle.

Genetic Variation for Acetylene Reduction Rate and Other Characters in Alfalfa

The objective of this study was to determine the general (GCA) and specific (SCA) combining abilities of alfalfa (Medicago sativa L.) for rate of acetylene reduction, plant dry weight, N content (%), total plant N and nodule score. The parental clones were selected from the commercial cultivars ‘Beaver,’ ‘Roamer,’ ‘Saranac,’ and ‘Rambler.’ Five strains of Rhizobium meliloti Dang., including four single strains and one commercial inoculant ‘Balsac’ were used. The most effective strain of Rhizobium was NRG61, while RM110 was the poorest. Diallel analysis of the six‐parent half diallel cross revealed that mean squares of both GCA and SCA were highly significant for all characters except the SCA mean square for nodule score. The highly significant interactions of GCA and SCA with Rhizobium strains suggested differential expressions of gene effects for alfalfa genotypes with different strains of Rhizobium. The GCA variance components were higher than SCA for total plant dry weight, total plant N and nodule score. This suggested that the major portion of the total genetic variation was additive. Recurrent selection for these characters should be possible. However, the additive and non‐additive gene effects were equally important for acetylene reduction rate with Rhizobium strains NRG43, NRG61, and NRG118. Reciprocal recurrent selection method might be necessary to improve this character with these single Rhizobium strains. Combining ability analysis for each of the parental clones indicated that Clone 4 had consistently high and positive GCA effects over all Rhizobium treatments. Clone 2 was on the other extreme with negative GCA effects in all cases. None of the other parental clones produced consistently positive GCA effects across all the Rhizobium strains.

Further Studies on the Reestablished Populations Derived from Chinta and the New Sweet Corn Composite

Further examination of the performance of reestablished populations from Chinta revealed that the variety can be improved by three recurrent selection methods. However, genotype-environment interactions affected yield performance making it very difficult to decide which method is more effective in improving the yielding ability of Chinta. The Syn1 did not differ very much from Syn2 in respect to all the characters measured. It is proposed that farmers can save their own seed for later generations of production. The newly developed sweet corn composite also gave a relatively higher yield compared to Chinta. This promising new composite may become another sweet corn variety for commercial production in our country.

A Model for Evaluating Progress from Recurrent Selection1

A model was developed to study the relationship between the change in the mean and changes of allelic frequencies in improved populations arising from recurrent selection. The change in the mean in the improved populations is a function of Δp, the weighted average change in allelic frequency, α, the average effect of a gene substitution in the base population, and R, the change in inbreeding depression in the improved populatious.The model is illustrated by use of data from two studies designed to evaluate recurrent selection methods in corn (Zea mays L.). The analysis indicated significant changes in the weighted average change in allelic frequency and in the amount of inbreeding depression in these populations. Direct and indirect effects of selection were not significantly different in most of the populations studied.

Efficiency changes due to use of doubled-haploids in recurrent selection methods

Efficiency comparisons are made among standard recurrent selection methods and for the same methods modified by the inclusion of haploid and cloning techniques. These comparisons are made with respect to five different gene models representing different levels of heritability and also with respect to unrestricted versus restricted total plant numbers.When comparisons are made either among the standard diploid or among the modified haploid selection methods, the advantages of clonal and general combining ability selection over individual selection largely disappear when a restriction on total plant numbers is imposed. However, the very considerable advantages of haploid over diploid selection methods, measured on a per cycle basis, do not disappear when total plant numbers are restricted.When the genetic gains are measured on a yearly basis, it becomes clear that the key to the successful inclusion of the haploid technique, as a device to increase the efficiency of standard recurrent selection methods, is the development of rapid doubled-Haploid extraction procedures.

Performance of Original and Advanced Maize Populations and Their Diallel Crosses1

Six maize (Zea mays L.) breeding populations, 7 advanced populations developed from them by recurrent selection, diallel crosses among all 13 populations, and 9 check hybrids were evaluated in 17 environments during 1970 and 1971. The objective was to evaluate, under a wide range of environmental conditions, observed progress from three methods of recurrent selection and to estimate changes in genetic parameters obtained from a diallel of the original populations versus estimates from a diallel of the advanced populations. VCBS(S)C4 and VCBS(HT)C3 were about 20% higher yielding than VCBS; this improvement was expressed in their population crosses. Selection also increased the environmental response (b1) of these populations and their crosses. Very little improvement was detected for the other populations or their crosses. Source materials and environmental conditions under which recurrent selection trials are conducted may be as important as the selection method used.Population and average heterosis effects explained most of the variation among entries. Hence, relative performance of the population crosses could be predicted reasonably well by population performance per se. Yields of the best population crosses did not differ significantly from yields of the hybrid checks. Extraction of inbred lines from VCBS(S)C4 or VCBS(HT)C3 to be used with lines extracted from BSSS(HT)C7 or PHWI(M)C9 should resuit in superior hybrids with a wide range of adaptation.

Comparison of Three Methods of Recurrent Selection in Maize1

Concurrent recurrent selection experiments were conducted for five cycles to compare three methods of selection for grain yield in maize (Zea mays L.): (1) combining ability with an inbred line (Inbred Tester Method), (2) combining ability with the broad‐base parental population (Parental Tester Method), and (3) yield S2 lines per se (S2 Progeny Method). The 15 selected populations were then crossed with the parental population and with another broad‐base synthetic to evaluate changes in general combining ability, and also were tested as randommated and selfed populations per se.A significant linear increase in general combining ability over cycles was obtained for all methods, but the Inbred Tester Method was significantly more effective than the other two methods (4.4% gain per cycle, compared with 2.4 and 2.0% for the Parental Tester and S2 Progeny Methods, respectively). There was no significant difference among methods for yield of random‐mated selected populations when adjustments were made for differences in rate of inbreeding.The results indicate that the inbred tester used was homozygous recessive at many important loci. This would result in larger testcross variances and more successful selection of dominant favorable alleles than is possible with a broad‐base tester, which probably has intermediate gene frequencies at most loci. The slow progress in combining ability improvement with the S2 Progeny Method suggests that this method also was not effective in fixing dominant favorable alleles.

Evaluation of Synthetic Populations Developed from a Maize Variety (BSK) by Two Methods of Recurrent Selection1

The effectiveness of half‐sib selection with a doublecross tester and S1 selection per se was evaluated following four cycles of selection in BSK (the Krug Hi I syn. 3 strain of ‘Krug Yellow Dent’). Five populations, BSK CO, BSK(HT)C2, BSK(S)C2, BSK(HT)C4, and BSK(S)C4, were selfed, sibbed, and crossed in a diallel series. They were also test‐crossed to four single‐cross testersThe average of the four single‐cross testcross yields of the BSK (S) populations increased 10.6% during the four cycles, and the BSK(HT) populations increased 5.7%. The selfing series populations performed better than the testcross series populations when selfed, as indicated by a 38.7% increase for the BSK(S) bulk S1's compared with a 12.0% increase for the BSK(HT) bulk S1s. The populations per se increased 16.3% in the selfing series and 6.3% in the testcross series. The BSK(HT) × BSK(S) crosses exhibited heterosis, which indicated that the two methods developed populations that differed in gene frequency.This study has shown that the mean yield and the general combining ability of BSK were significantly improved by four cycles of selection with both methods of recurrent selection, but S1 selection per se was more effective.