Cycles Of Recurrent Selection Research Articles

Registration of ‘Espresso’ lowland switchgrass

Abstract‘Espresso’ (Reg. no. CV‐293, PI 687202) is a lowland ecotype (Gulf sub‐population) of switchgrass (Panicum virgatum L.) developed and released by Mississippi State University and the Mississippi Agricultural and Forestry Experiment Station. Espresso was developed from seven cycles of phenotypic recurrent selection for rapid seed germination without stratification. All cycles of selection were made using seed harvested from open‐pollinated isolation blocks containing approximately 100 mother plants. Germination was assessed in laboratory conditions for 15 years, culminating in 2 years of field‐based germination and emergence evaluation at five locations across Mississippi. Over a 2‐year period, germination and emergence of Espresso was significantly greater (P < 0.05) than seed from ‘Alamo’ and ‘Kanlow’. Field testing revealed Espresso as having significantly (P < 0.05) greater establishment success (mean number of seedlings per linear 30 cm) when compared to Alamo. Espresso was released based on the need for southeastern US‐adapted germplasm that possesses enhanced germination characteristics.

Effects of Recurrent Selection on Population Structure and Allele Frequencies in the M3S Maize Population

The effects of four cycles of recurrent selection on the allele frequencies of simple sequence repeat (SSR) markers and population structure were examined in the Maksimir 3 Synthetic (M3S) maize population (Zea mays L.). Genotyping of 32 plants from each selection cycle at 38 SSR loci revealed that the mean number of alleles per locus and the mean expected heterozygosity were preserved across selection cycles, indicating the maintenance of sufficient genetic variability in the population required for future genetic gain. The Waples test of selective neutrality revealed that genetic drift was the main force in changing allele frequencies in the population. The proportion of selectively non-neutral loci in single cycles of selection varied between 16% and 37%. Some non-neutral loci shared the same genomic locations with previously published QTLs controlling important agronomic traits. An analysis of molecular variance revealed that 5.6% of the genetic variation occurred among and 94.4% within cycle populations. Between 5% and 29% of loci were found to be in a significant Hardy–Weinberg (HW) disequilibrium, with the majority showing an excess of homozygosity. The excess of homozygosity at several loci was highly consistent across cycle populations, suggesting positive assortative mating as a possible cause of the observed HW disequilibrium. Linkage disequilibrium (LD) tests revealed that the M3S population was essentially in linkage equilibrium. The proportion of pairs of loci in significant LD varied from 0.1% to 1.8% across selection cycles, probably due to the effects of genetic drift and epistatic selection.

Recurrent selection effects on the genetic structure of maize landrace assessed by SSR markers

Recurrent selection method was applied in one maize landrace (Zea mays L.) population, Macaco, for one cycle of selection. In the present study the changes in genetic structure were investigated at 18 microsatellite loci. A total of 81 alleles were observed in cycle 0 (C0) population which 79 were maintained in cycle 1 (C1) population. Thus, a reduction of 2.5% in the allele frequency was observed after one cycle of selection in C1 population. The heterozygozity reduction was also observed after one cycle of selection. In nearly 44% and 55% of the loci evaluated in C0 and C1 populations, respectivelly, the changes in allelic frequencies in populations were not due exclusively by genetic drift effects. Although few changes have been observed in allelic frequencies, the grain yield increase was observed after one cycle of recurrent selection. The genetic differentiation estimated by GST and RST values, for microsatellite data between C0 and C1 populations indicate that genetic variability degree was maintained in C1 population. This result suggest that C1 population can be used in a new recurrent selection cycles.

Genome-wide association analysis of plant architecture traits using doubled haploid lines derived from different cycles of the Iowa Stiff Stalk Synthetic maize population.

Selection in the Iowa Stiff Stalk Synthetic (BSSS) maize population for high yield, grain moisture, and root and stalk lodging has indirectly modified plant architecture traits that are important for adaptation to high plant density. In this study, we developed doubled haploid (DH) lines from the BSSS maize population in the earliest cycle of recurrent selection (BSSS), cycle 17 of reciprocal recurrent selection, [BSSS(R)17] and the cross between the two cycles [BSSS/BSSS(R)C17]. We aimed to determine the phenotypic variation and changes in agronomic traits that have occurred through the recurrent selection program in this population and to identify genes or regions in the genome associated with the plant architecture changes observed in the different cycles of selection. We conducted a per se evaluation of DH lines focusing on high heritability traits important for adaptation to high planting density and grain yield. Trends for reducing flowering time, anthesis-silking interval, ear height, and the number of primary tassel branches in BSSS(R)17 DH lines compared to BSSS and BSSS/BSSS(R)C17 DH lines were observed. Additionally, the BSSS(R)C17 DH lines showed more upright flag leaf angles. Using the entire panel of DH lines increased the number of SNP markers identified within candidate genes associated with plant architecture traits. The genomic regions identified for plant architecture traits in this study may help to elucidate the genetic basis of these traits and facilitate future work about marker-assisted selection or map-based cloning in maize breeding programs.

Cinco ciclos de seleção recorrente intrapopulacional em progênies de meioirmãos de milho fresco

ABSTRACT Fresh corn is a highly appreciated vegetable in Brazil; this crop has high added value and profitability when compared to dry corn. Despite the consumer market demand for quality, cultivars are not launched every crop season and there is a small number of cultivars available to growers. This denotes a need for breeding programs focused on generating information and genotypes that can occupy this market niche. The objective of this work was to evaluate the progress of five cycles of intrapopulation recurrent selection in half-sib progenies of fresh corn, in the southwest region of Goiás. A randomized block experimental design was used, with evaluation of 64 progenies of corn half-sib progenies and selection intensity of 30% per cycle, with three replications, in the 2011-2012, 2013-2014, 2015-2016, 2017-2018, and 2020-2021 summer crop seasons. The half-sib progenies of fresh corn exhibited genetic variability through intrapopulation recurrent selection in the different selection cycles, which is still promising for further selections after five cycles, with evaluation of 64 progenies per cycle. The base population from crossings between hybrids for tropical and temperate climates showed to be promising for increasing the genetic base of fresh corn populations, with satisfactory gains over the five cycles, presenting mean heritability between the cycles of approximately 78.9% for relative chlorophyll index, 62.2% for plant height, 75.1% for ear insertion height, 70% for ear diameter, 56.6% for ear length, 71.4% for unhusked ear yield, and 71% for marketable ear yield.

Realized genetic gains via recurrent selection in a tropical maize haploid inducer population and optimizing simultaneous selection for the next cycles

AbstractPlant breeders widely use recurrent selection schemes to increase the frequency of favorable alleles for quantitative traits in a population. Although simultaneous selection is complex because it involves several traits combined with selection cycles, the use of selection indexes (SI) is applied to increase the chance of success of the breeding program. Despite many indices are available in the literature, simulations can help breeders to determine which selection index can be better adjusted considering the selection goals, the intensity, and the genetic correlation among traits over breeding cycles. In this context, we estimated the realized genetic gains in a tropical maize haploid inducer population after two cycles of recurrent selection, using external testers and optimizing the simultaneous selection for this breeding population in the long term via stochastic simulations. Furthermore, we proposed a new approach to optimize the initial weights by applying Smith‐Hazel method to maximize the genetic gains for all traits in a balanced way. Overall, the estimated gains in real induction rate were about 63% per cycle, improving the population performance from 0.8% to 2.8%. Moreover, our results confirm that the traditional Smith‐Hazel approach outperformed other methods for long‐term response to selection. Finally, recurrent selection with external testers may be a suitable method to improve the haploid induction rate in tropical maize populations.

Molecular characterization of doubled haploid lines derived from different cycles of the Iowa Stiff Stalk Synthetic (BSSS) maize population.

Molecular characterization of a given set of maize germplasm could be useful for understanding the use of the assembled germplasm for further improvement in a breeding program, such as analyzing genetic diversity, selecting a parental line, assigning heterotic groups, creating a core set of germplasm and/or performing association analysis for traits of interest. In this study, we used single nucleotide polymorphism (SNP) markers to assess the genetic variability in a set of doubled haploid (DH) lines derived from the unselected Iowa Stiff Stalk Synthetic (BSSS) maize population, denoted as C0 (BSSS(R)C0), the seventeenth cycle of reciprocal recurrent selection in BSSS (BSSS(R)C17), denoted as C17 and the cross between BSSS(R)C0 and BSSS(R)C17 denoted as C0/C17. With the aim to explore if we have potentially lost diversity from C0 to C17 derived DH lines and observe whether useful genetic variation in C0 was left behind during the selection process since C0 could be a reservoir of genetic diversity that could be untapped using DH technology. Additionally, we quantify the contribution of the BSSS progenitors in each set of DH lines. The molecular characterization analysis confirmed the apparent separation and the loss of genetic variability from C0 to C17 through the recurrent selection process. Which was observed by the degree of differentiation between the C0_DHL versus C17_DHL groups by Wright's F-statistics (FST). Similarly for the population structure based on principal component analysis (PCA) revealed a clear separation among groups of DH lines. Some of the progenitors had a higher genetic contribution in C0 compared with C0/C17 and C17 derived DH lines. Although genetic drift can explain most of the genetic structure genome-wide, phenotypic data provide evidence that selection has altered favorable allele frequencies in the BSSS maize population through the reciprocal recurrent selection program.

Effect of three cycles of recurrent selection for yield in four Spanish landraces of maize

Landraces of maize (Zea mays L.) have a variability not found in the elite hybrids due to the bottleneck during selection. There is a renewed interest in using that variability, incorporating alleles for specific traits, or widening the general variability of elite germplasm. In Europe, there is also an interest in the direct use of local landraces by farmer’s associations seeking agriculture that preserves crop diversity. Pre-breeding programs are aimed to reduce the yield gap among landraces and improved materials. In the Misión Biológica de Galicia we have carried out three cycles of a S1 recurrent selection program for yield on four local landraces from Northwestern Spain with the objective of obtaining improved populations that might be cultivated by farmers and that could be used as sources of superior inbred lines. One hundred plants were selfed in each landrace and the S1 families were evaluated in a 10 × 10 simple lattice. The 20 S1 families with the highest grain yields were randomly intercrossed to form the selected population of each landrace. After three cycles of selection, each population and its cycles of selection were evaluated in three locations for two years. All the populations had a consistent yield gain in the first cycle of selection. However, the response in later cycles differed among the populations: one population had a continuous increase of 21% per cycle while two populations had a reduced yield in the last cycles. Our results highlight the need to include secondary traits to avoid unintentional indirect effects. We conclude that, in pre-breeding programs, it could be worthy to use large effective numbers to prevent inbreeding depression, particularly when the objective is the direct use of improved landraces. Another conclusion is that recurrent selection does not seem to be as efficient on European germplasm as it is on Corn Belt varieties. Finally, obtaining valuable new germplasm requires a sustained, long-term effort.

Optimising selection in full-sib progeny of the cashew

In Brazil, the productivity and quality of the peduncle and nut of the cashew have increased significantly due to the use of binomial hybridisation-cloning. In the present research, genetic parameters (variance components – individual REML) and genetic values (mean components – individual BLUP) were estimated in a test of full-sib segregating progenies, aiming at the selection of superior cashew progenies and individuals. A controlled-pollination, segregating population from the cashew genetic breeding program of Embrapa Agroindústria Tropical, comprising four different progenies, each represented by 48 full-sib (FS) individuals, were evaluated over six consecutive crops. The following traits were evaluated: nut yield, mean nut weight, reaction to Anacampsis phytomiella, and reaction to oidium (powdery mildew). The experimental design was of randomised blocks, with four replications and 12 plants per plot. The REML/BLUP geneticstatistical procedure was used to optimise the selection process. It seems reasonable to opt for a selection limit of 14 individuals with superior behaviour to comprise the recombination unit of the next cycle of recurrent selection using the remaining seeds from this breeding population. Plants 25 and 27 from the progeny identified as having the best performance (FS 13/3) for direct cloning were selected to comprise the local trial of the cashew genetic breeding program.

Recurrent Interpopulation Selection in Popcorn: From Heterosis to Genetic Gains

In view of the need to develop new popcorn cultivars and considering the uncertainties in choosing the most appropriate breeding methods to ensure consistent genetic progress, simultaneously for both popping expansion and grain yield, this study addressed the efficiency of interpopulation recurrent selection regarding genetic gains, the study of the response in genetic parameters as well as heterotic effects on the control of the main agronomic traits of popcorn. Two populations were established, Pop1 and Pop2. A total of 324 treatments were evaluated, which consisted of 200 half-sib families (100 from Pop1 and 100 from Pop2), 100 full-sib families from the two populations and 24 controls. The field experiment was arranged in a lattice design with three replications in two environments, in the north and northwest regions of the State of Rio de Janeiro, Brazil. The genotype × environment interaction was partitioned and the genetic parameters, heterosis and predicted gains were estimated by the Mulamba and Mock index, based on selection results in both environments. The genetic parameters detected variability that can be explored in successive interpopulation recurrent selection cycles. Exploring heterosis for GY, PE and yield components is a promising option to increase grain yield and quality. The Mulamba and Mock index was efficient in predicting the genetic gains in GY and PE. Interpopulation recurrent selection proved effective to provide genetic gains for traits with predominantly additive and dominance inheritance.

Registration of ‘Sims’ little bluestem

Abstract‘Sims’ (Reg. no. CV‐17, PI 700041) little bluestem [Schizachyrium scoparium (Michx.) Nash] was selected for greater 7‐d laboratory seed germination and superior field emergence. Two cycles of recurrent selection were used to develop Sims from little bluestem germplasm UC‐2 (PI 676265). Cycle 1 consisted of germinating 3,500 open‐pollinated pure seed (spikelets) of germplasm UC‐2 (designated UC‐2 C0) in water of –0.8 MPa potential for 7 d. All seed that germinated in 7 d were selected to create population UC‐2 C1. Cycle 2 selection was identical to Cycle 1 selection except that population UC‐2 C1 was used to create population UC‐2 C2 = Sims. The 7‐d seed germination of Sims in deionized water averaged 68% compared with 39, 53, and 71 for ‘Cimarron’, ‘Aldous’, and ‘Ahring’, respectively. Sixty days after field planting, plant population density of Sims averaged 8.9 plants m−2 compared with 7.1, 8.4, and 9.4 plants m−2 for Aldous, Cimarron, and Ahring, respectively. Thus, recurrent selection for increased seed germination in a negative water potential resulted in a little bluestem population capable of rapid seed germination and field emergence. Sims little bluestem is useful for livestock grazing, wildlife habitat, soil and water conservation, renewable energy, and horticultural landscapes in the U.S. southern Great Plains. Sims was released cooperatively by the USDA‐ARS and USDA‐NRCS.

Germination and field establishment of Indiangrass populations selected for greater laboratory seed germination in a simulated dry condition

Germination and field establishment of Indiangrass populations selected for greater laboratory seed germination in a simulated dry condition

Additive and Non-Additive Effects on the Control of Key Agronomic Traits in Popcorn Lines under Contrasting Phosphorus Conditions.

Phosphorus is a non-renewable natural resource that will run out of reserves in the upcoming decades, making it essential to understanding the inheritance of nutrient use efficiency for selecting superior genotypes. This study investigated the additive and non-additive effects of commercially relevant traits for the popcorn crop (grain yield—GY, popping expansion—PE, and expanded popcorn volume per hectare—PV) in different conditions of phosphorus (P) availability in two locations in Rio de Janeiro State, Brazil. Six S7 lines previously selected for P use—L59, L70, and P7, efficient and responsive; and L54, L75, and L80, inefficient and non-responsive—were used as testers in crosses with 15 progenies from the fifth cycle of intrapopulation recurrent selection of UENF-14, with adaptation to the North and Northwest regions of Rio de Janeiro State. Using the Griffing diallel analysis, P use efficiency was predominantly additive in the expression of PE, and non-additive effects were prominent for GY and PV. For obtaining genotypes that are efficient for phosphorus use, it is recommended that heterosis with parents that provide additive gene accumulation for PE be explored.

Recurrent haploid selection in a population of sweet corn (Zea mays convar. saccharata)

AbstractRecurrent haploid selection is based on the phenotype of haploid plants. This selection method was reported to be very effective because of the high selection pressure. The aim of this study was to quantify the effect of five generations of recurrent haploid selection on a sweet corn population developed by intercrossing 40 hybrid cultivars. We compared the initial population, five cycles of recurrent haploid selection, and mass selection after five cycles in six environments. The results indicated that recurrent haploid selection had no positive effect on yield or quality. For the traits tillering, tip fill, total yield and total number of ears, significant changes from cycle to cycle were observed but in differing directions. The performance per se of single haploid plants has probably a low correlation to their combining ability in a population. Positive mass selection of the best ears resulted in no improvement of total yield, a reduction of marketable yield and about 2‐day delay of flowering. In conclusion, recurrent haploid selection based on the phenotype of individual plants was not an efficient method to improve the sweet corn population investigated.

Study of genetic architecture of grain yield and quality traits through generation mean analysis in rice (Oryza sativa L.)

A perusal of gene effects in generation mean analysis for three crosses viz., BPT 5204 x IR 36, BPT 5204 x NLR 34449 and RNR 2465 x IR 64 revealed the presence of a significant proportion of epistatic effects besides the major components viz., additive (d) and dominance (h) gene effects for important yield and quality attributes. Partitioning of variance indicating that the mean values (m) for gene effects were highly significant in all the three crosses for most of the traits, the results of dominance (h) and dominance × dominance (l) type interactions revealed that duplicate type of epistasis was prevalent for most of the traits in all the six crosses except in RNR 2465 x IR 64 for the number of filled grains per panicle; BPT 5204 x NLR 34449 for kernel breadth and kernel elongation ratio and BPT 5204 x IR 36 for harvest index where, complementary gene action played a vital role in the inheritance of the traits. Therefore, improvement of these traits appears to overwhelmed with difficulties as simple selection techniques will not be able to fix superior lines in the early segregating generations. Postponement of selection for superior lines to later generations in pedigree breeding will be effective. However, one or two cycles of recurrent selection followed by pedigree breeding will be effective and useful to utilize both additive and non-additive gene effects. The predominance of dominance and epistatic interactions in all the crosses for quality traits indicates that selection would be more effective if the dominance and epistatic effects are first reduced by a few generations of selfing.  Keywords: Rice, generation mean analysis, gene action

Heterosis and Responses to Selection in Orange-Fleshed Sweetpotato (Ipomoea batatas L.) Improved Using Reciprocal Recurrent Selection.

Sweetpotato is a highly heterozygous hybrid, and populations of orange-fleshed sweetpotato (OFSP) have a considerable importance for food security and health. The objectives were to estimate heterosis increments and response to selection in three OFSP hybrid populations (H1) developed in Peru for different product profiles after one reciprocal recurrent selection cycle, namely, H1 for wide adaptation and earliness (O-WAE), H1 for no sweetness after cooking (O-NSSP), and H1 for high iron (O-HIFE). The H1 populations were evaluated at two contrasting locations together with parents, foundation (parents in H0), and two widely adapted checks. Additionally, O-WAE was tested under two environmental conditions of 90-day and a normal 120-day harvest. In each H1, the yield and selected quality traits were recorded. The data were analyzed using linear mixed models. The storage root yield traits exhibited population average heterosis increments of up to 43.5%. The quality traits examined have exhibited no heterosis increments that are worth exploiting. The storage root yield genetic gain relative to the foundation was remarkable: 118.8% for H1-O-WAE for early harvest time, 81.5% for H1-O-WAE for normal harvest time, 132.4% for H1-O-NSSP, and 97.1% for H1-O-HIFE. Population hybrid breeding is a tool to achieve large genetic gains in sweetpotato yield via more efficient population improvement and allows a rapid dissemination of globally true seed that is generated from reproducible elite crosses, thus, avoiding costly and time-consuming virus cleaning of elite clones typically transferred as vegetative plantlets. The population hybrid breeding approach is probably applicable to other clonally propagated crops, where potential for true seed production exists.

TX‐BHS berseem clover germplasm

AbstractTX‐BHS (Reg. no. GP‐312, PI 699627) is a germplasm line of berseem clover (Trifolium alexandrinum L.) selected for increased cold tolerance and hard seed production. This germplasm line was developed by Texas A&M AgriLife Research at Overton and is intended to extend the range and utility of this annual clover species. Berseem is well adapted to wet and waterlogged soils and has potential for expanded use in both pasture and cover crop systems. Improved hard seed production would allow expanded use of berseem in reseeding pasture and cropping systems. Three cycles of recurrent half‐sib selection and two cycles of recurrent phenotypic selection were applied to the variable base population (Mississippi Winter Hardy Berseem) at Overton, TX, from 1982 to 1988. Selection was successful in improving hard seed levels of TX‐BHS relative to ‘Bigbee’ berseem. Selection for winter survival and reduced cold damage caused a reduction in winter growth of TX‐BHS berseem relative to Bigbee berseem. This growth pattern shift was only observed in only one trial. The actual impact of selection on winter survival and cold tolerance of TX‐BHS berseem needs further study.

Study of gene action for yield and quality traits in rice (Oryza sativa L.)

The present experiment was conducted to study the gene action, heterosis, inbreeding depression and heritability for different yield and quality traits in the cross WGL 48684 x IR 36. Analysis of heterosis revealed that most of the traits show duplicate type of epistasis which is non- fixable and cannot be exploited through the general breeding procedures of self pollinated crops. Additive gene effect and complementary epistasis plays a lead role for plant height, number of ear bearing tillers per plant, kernel breadth and amylase content and they can easily be exploited for developing fixed lines. Significant inbreeding depression was found for ear bearing tillers per plant, SPAD Chlorophyll Meter Reading (SCMR), harvest index, grain yield, head rice recovery and kernel elongation ratio. Therefore, few cycles of recurrent selection followed by pedigree method would be effective and useful to utilize all types of gene effects by maintaining considerable heterozygosity through mating of selected plants in early segregating generations.

RESPONSE OF THREE CYCLES OF S1 RECURRENT SELECTION FOR GRAIN YIELD IN MAIZE POPULATION SAKHA 14

The new white composite maize population Sk14 was developed in Sakha Research Station, Egypt. This population which showed heterotic behavior was subjected to three cycles of S1 recurrent selection to improve yielding potentiality. The three cycles were made during the period from 2010 to 2018. The original cycle, Sk14 C0 and three cycles of selection, Sk14 C1, Sk14 C2 and Sk14 C3 and two populations Gz-2 and AED as checks were evaluated at four locations for grain yield during 2020 season. The phenotypic, genotypic, genotypic × environment interaction variances, broad sense heritability and the expected genetic gain% for Sk14 C1 were higher than Sk14 C2 and Sk14 C3, indicating that the genetic variability was decreased with advanced cycles of selection. Grain yield increased linearly during three cycles of the S1 recurrent selection, the highest mean obtained in C3 followed C2, C1 and C0. The higher percentage gain cycle-1 was realized in C3 than C0 (14.33%) followed C3 than C1 (9.06%) and C3 than C2 (8.44%), indicating that the S1 recurrent selection employed was effective in improving grain yield. The population Sk14 C3 had the highest grain yield and most stable population based on 4 (CV%, bi, Pi and Si(1)) out of 5 parametric stability statistics, this meaning that this population could be used in maize breeding program as source for deriving maize inbred lines of tolerance to different production conditions.

Registration of ‘Ahring’ little bluestem

Abstract‘Ahring’ (Reg. no. CV‐16, PI 699123) little bluestem [Schizachyrium scoparium (Michx.) Nash] was selected for greater 7‐d seed germination at low water potential and superior field emergence. Two cycles of recurrent selection were used to develop Ahring from germplasm UO‐2. Cycle 1 consisted of germinating 3,500 open‐pollinated pure seed of germplasm UO‐2 (designated UO‐2 C0) in water of −0.8 MPa potential for 7 d. All spikelets that germinated in 7 d (∼250) were selected to create population UO‐2 C1. Cycle 2 selection was identical to Cycle 1 selection except that population UO‐2 C1 was used to create population UO‐2 C2. The 7‐d laboratory seed germination of Ahring was 17% higher than UO‐2 C0 in deionized water. Sixty days after planting, field emergence of Ahring (35%) was greater than either population UO‐2 C1 (32%) or UO‐2 C0 (22.0%) or the cultivars ‘Cimarron’ (32%) or ‘Aldous’ (27%). Thus, recurrent selection for increased seed germination in a negative water potential resulted in a little bluestem population capable of greater field emergence. Ahring little bluestem is useful for wildlife habitat, grazing, soil stabilization, water conservation, renewable energy, and horticultural landscapes in the south‐central and southern Great Plains of the United States. Ahring was cooperatively released by the USDA‐ARS and the USDA‐NRCS.