Realized Heritability Estimates Research Articles

Phenotypic Selection and Bulked Sergeant Analysis for 1000-Kernel Weight under Heat Stress in Durum Wheat

Divergent phenotypic selection for 1000-kernel weight (TKW) was performed under heat stress in a population of 120 F7 recombinant inbred lines (RILs) of durum wheat. The direct response to selection for TKW and correlated response in grain yield per plant (GYP) were assessed under favorable and heat stress conditions. Considerable genetic variations were found among the tested RILs for TKW and GYP. Under heat stress, mean TKW of F7 RILs selected in the high and low directions were 62.28 and 34.42g, respectively. Positive and highly significant responses to selection were obtained for TKW in the high (14.92 and 16.29%) and low (20.78 and 26.88%) directions under favorable and heat stress conditions, respectively. Selection for higher TKW produced positive and highly significant correlated response in GYP under heat stress (11.05%), whereas selection for lower TKW produced positive and highly significant correlated responses in GYP under favorable (11.13%) and heat stress (19.33%) conditions. High realized heritability estimates were obtained for TKW (0.74 and 0.75) and GYP (0.65 and 0.71) under favorable and heat stress conditions, respectively. F8 RILs derived from selection for higher TKW showed higher heat tolerance index (averaged 1.20) than RILs selected for lower TKW (0.52), indicating the usefulness of selection for higher TKW in improving heat tolerance. Bulked segregant analysis with 40 simple sequence repeats (SSR) markers identified seven positives alleles located on 2A (1), 3B (2), 4A (1), 5A (1), 6A (1) and 7B (1) chromosomes that were associated with higher TKW as an indicator for heat tolerance.

SELECTION OF THE NIGERIAN INDIGENOUS FOWL FOR 12-WEEK BODY WEIGHT

A FOUNDATION stock of 1171 male and 1210 female indigenous fowl supplied a breeding population which increased from 858 — 1627 over a period of seven generations (about 71 years) During the first three generations 30-38 % of males and females and subsequently about 2.4 — 2.7% males and 25 % females were selected positively for 12 weeks body weight. A non-selected flock mated population of 455 — 615 females and 53 — 70 males per generation provided basis for determining the response to selection. This amounted to 40.1 ± 0.37g, 36.9 ± 0.37g and 39.4 ± 0.37g per generation for male, female and the sexes combined respectively. The realised heritability estimates 0.27 ± 0 03 — 0.28 ± 0.03 appeared close to values obtained by within generation hierachial classification and suggested, no sex-linked effects for the selected trait in this population. The relatively low ultimate male and female mean weights, 760.0 ± 63.1g and 673.5 1 ± 79.0g respectively combined with the marked reduction in the variation of body weight that occurred as selection progressed indicate that the Nigerian indigenous fowl is not a potential broiler strain.

Selection, Realized Heritability, and Fitness Cost Associated With Dimethoate Resistance in a Field Population of Culex quinquefasciatus (Diptera: Culicidae).

Mosquitoes are known to be vectors of numerous diseases leading to human morbidity and mortality at large scale in the world. Insecticide resistance has become a serious concern in controlling the insect vectors of public health importance. Dimethoate is an organophosphate insecticide used to control different insect pests including mosquitoes. Biological parameters of susceptible, unselected, and dimethoate-selected strains of Culex quinquefasciatus Say were studied in the laboratory to recognize resistance development potential and associated fitness cost. The dimethoate-selected strain showed 66.48-fold resistance to dimethoate compared with the susceptible strain after three continuous selections of generations. Realized heritability estimates of dimethoate resistance in Cx. quinquefasciatus yielded a value of 0.19. In dimethoate-selected strain, the biological traits including larval weight, survival from first instar to pupae, fecundity, number of next-generation larvae, relative fitness, net reproductive rate, intrinsic rate of natural increase, and biotic potential were significantly reduced as compared with the unselected strain. However, adult longevity, mean relative growth rate, weight of egg raft, female ratio, pupal duration, and emergence rate of the dimethoate-selected strain did not differ significantly compared with that of the unselected strain. This study provides useful information to devise retrospective management strategy for dimethoate resistance in Cx. quinquefasciatus.

Divergent Selection for Fiber Length and Bundle Strength and Correlated Responses in Cotton

Cotton (Gossypium spp.) breeders must develop cultivars to meet the demand for longer, stronger, and more uniform fibers. In the current study, two cycles of divergent selection for fiber upper‐half mean length (UHML) and bundle strength (Str) were conducted within five diverse parental combinations selected based on their potential for the genetic improvement of fiber quality. Realized heritability estimates for UHML and Str were calculated for each cycle, and correlated responses among fiber properties and lint percent were measured as they responded to selection for UHML and Str. The results suggest that early‐generation selection for UHML and Str is an effective strategy for the genetic improvement of fiber quality at College Station, TX. Although UHML and Str were consistently negatively correlated with lint percent, the results demonstrate that sufficient variation for fiber quality exists within the Texas A&M AgriLife Research upland cotton germplasm to improve UHML and Str without a concomitant reduction in lint percent. A negative phenotypic correlation between UHML and fiber elongation at break was also observed and was independent of the association between Str and fiber elongation at break in multiple populations. These findings suggest that further investigation into the relationship between UHML and fiber elongation within the Texas A&M AgriLife Research germplasm is warranted.

Responses to two-way selection on growth in mass-spawned F1 progeny of Argopecten irradians concentricus (Say)

In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop (Argopecten irradians concentricus) was examined to evaluate the efficacy of a selection program currently being carried out in Beibu Bay in the South China Sea. A total of 146 adult scallops were randomly selected from the same cultured population of A. i. concentricus, and divided into two groups in shell length (anterior-posterior measurement): large (4.91–6.02 cm, n=74) and small (3.31–4.18 cm, n=72). At the same time, a control group was also randomly sampled (4.21–4.88 cm, n =80). Mass-spawned F 1 progenies from the three size groups were obtained and reared under identical conditions at all growth phases. The effects of two-way (or upward-downward) selection on fertilization rate, hatching rate, survival rate, daily growth in shell length and body weight were assessed in the three size groups. Results show that significant differences (P 0.05), among the three groups. The hatching rate, survival rate and daily growth of the progeny of large-sized parents were greater than those of the control group (P<0.05), which in turn were larger than those of small-sized group (P<0.05). Responses to selection by shell length and body weight were 0.32 ± 0.04 cm and 2.18 ± 0.05 g, respectively, for the upward selection, and −0.14 ± 0.03 cm and −2.77 ± 0.06 g, respectively, for the downward selection. The realized heritability estimates of shell length and body weight were 0.38 ± 0.06 cm and 0.22 ± 0.07 g for the upward selection, and 0.24 ± 0.06 cm and 0.37 ± 0.09 g for the downward selection, respectively. The change in growth by bidirectional selection suggests that high genetic variation may be present in the cultured bay scallop population in China.

Selection response and realized heritability for growth in three stocks of the Pacific oyster Crassostrea gigas

To estimate response to selection and realized heritability for shell height, a one-generation selection was performed in the Pacific oyster Crassostrea gigas using three stocks from China (stock C), Japan (stock J), and Korea (stock K). Applying about the same intensity of selection in the upward direction, three selected and three control lines were created, which were reared under the same environmental conditions at larvae, spat, and grow-out stages. Stock C and stock J showed significantly higher response to selection and realized heritability than stock K at spat and grow-out stages (P < 0.05). At harvest on day 360, the selected lines of stocks C, J, and K were 12.2, 12.2, and 7.9% larger than their control lines, respectively, for shell height. When averaged across the grow-out period, the genetic gain for stocks C, J, and K was 13.2 ± 1.2, 13.2 ± 1.0, and 7.2 ± 0.7%, respectively, and realized heritability was 0.334 ± 0.028, 0.402 ± 0.024 and 0.149 ± 0.027, respectively. The relatively high realized heritability estimate obtained for stock C and stock J indicates that there is genetic variation in the two stocks and that selective breeding by mass selection is very promising.

Realized heritability and genetic gains of three generation for superior growth in the pearl oyster Pinctada martensii

The pearl oyster Pinctada martensii is an important economic shellfish species and mainly cultured in the southern provinces of China. The species is cultured for marine pearl production. However, pearl quality has recently decreased because the cultured stocks had slow growth and mass mortalities caused by inbreeding depression. We have initiated a selective breeding program to improve the cultivated stocks since 2002. In 2004, a base population was developed by collecting the breeders from Beibuwan and Liushagang stocks. During the period of 2005–2007, a two successive generation selection for shell length in the base population was carried out to produce the second generation selected and unselected lines. In May of 2008, three types of lines were produced by selecting the breeders from the second generation selected and unselected lines. The three types of lines were designated as SS (Selected for three generations), SC (selected for the two generations) and CC (unselected for three generations). Realized heritability for the third generation, cumulative (over three generation) and current (for the third generation) genetic gains were evaluated by comparing the growth performance of three types of lines at days 8, 16, 45, 75, 180 and 360. It was found that the SS lines had significant larger mean shell length and shell height than the SC and CC lines at all sampling ages ( P < 0.05). The realized heritability estimate for adult shell length for the third generation was 0.41, similar with those detected for the first and second generation. The cumulative and current genetic gains for adult shell length were 20.94% and 13.27%, respectively. The present results indicate that there exists a high genetic variation in the population and mass selection is potential to improve pearl oyster stocks.

Response of Productive and Morphovegetative Traits of Globe Artichoke (Cynara cardunculus var. scolymus) to Mass Selection and Estimation of their Heritability

There have been few reports on genetic parameters or artificial selection for growth traits in globe artichoke (Cynara cardunculus var. scolymus), the study of the effect of one cycle of mass selection and realized heritability estimates would be valuable for planning breeding strategies in this species. A C0 segregating population was formed from the cross of two contrasting seed-grown cultivars, Imperial Star and Estrella del Sur FCA. Selected plants for productive traits were intercrossed to produce a C1 population. The C1 population along with the C0 population, both parents and the F1 were evaluated obtaining the response to selection and estimating realized heritability. Mass selection for increased yield and precocity was particularly successful, where for the first trait realized heritability reached 0.71 and 0.60 for the second one. For most traits, the observed values for realized heritability in the experiment (0.75, 0.61 and 0.52 for weight of the main head, marketable yield and length of the main head, respectively) indicate that a substantial part of the observed phenotypic variance is of additive nature. Therefore, in general, selection for these traits in seed-grown globe artichoke populations will be effective.

Realized heritability estimates during a cyclical process of selection and intercrossing in bread wheat and hexaploid triticale

This study was designed to compare realized heritability estimates for several traits of a selection index applied in rain fed bread wheat (Triticum aestivum L.) and hexaploid triticale (× Triticosecale Wittmack) recurrent selection programs. The experimental material consisted in C4–C5 triticale and C7–C8 bread wheat S0 progenies selected disruptively and evaluated as S1 derived families. The selection differential (SD) and the response to selection (RS) were estimated from the S0 progenies and the S1 derived families, respectively, as the differences (in percent) between high and low (=100) selection index group mean values. In bread wheat, significant differences between groups of S1 derived families were observed in the 7th cycle for all the studied traits; while only significant differences for harvest index were observed in the 8th cycle. Taking into account only the statistically significant differences between high and low selection index group mean values, the realized heritability estimates for grain yield, biomass yield and grain number were lower (7.0% to 11.2%) than those obtained for 1000-grain weight and harvest index (12.3% to 20.5%). The narrow germplasm base in triticale generated insignificant response to selection results.

Response to domestication and selection for growth in the European sea bass ( Dicentrarchus labrax) in separate and mixed tanks

Selective breeding of European sea bass ( Dicentrarchus labrax) receives a growing interest, as the estimated heritability of growth is medium to high. In this study, we compared the offspring of four groups of sea bass sires, mated with the same wild dams: wild ( W), first generation of domestication ( D), first generation of mass selection for length ( M), first generation of PROSPER-like selection for length ( P). The comparison was done both in replicated tanks (separate rearing) and in mixed tanks (mixed rearing) where sire origins were recovered by genotyping of eight microsatellite markers. Weight, length and growth rate were measured from day 238 post-fertilization (69 g mean weight) to day 611 post-fertilization (390 g mean weight). Both in mixed and separate tanks, both selected groups ( P, M) were larger than unselected groups ( W, D). No difference was seen at any time between W and D, nor between M and P. The selection response estimate on weight was larger in mixed tanks when compared to separate tanks (+ 42% in mixed tanks, + 23% in separate tanks at day 611), yielding realized heritability estimates of 0.60 and 0.34, respectively, and confirming the excellent potential of the species for growth improvement through selective breeding. Both selection response and the amplification effect between mixed and separate tanks decreased as rearing density increased. Our hypothesis is that selection response is magnified by competition in mixed tanks, while sub-optimal rearing conditions lower the observed selection response, more in separate tanks (where selected thus larger fish are at a higher density than unselected ones) than in mixed tanks (where all fish experience the same density effects).

Reduction in kernel weight as a potential indirect selection criterion for wheat grain yield under terminal heat stress

AbstractHeat is an important abiotic stress during wheat (Triticum aestivum L.) grain‐filling in South Asia. A study was undertaken to determine effectiveness of selection for reduction in 1000‐kernel weight (TKWR) under heat stress to increase grain yield. Selection was made for low and high TKWR and selected progenies were evaluated in timely and late seeded trials at two locations in Nepal in 2003. One thousand kernel weight (TKW), biomass yield, grain yield, harvest index (HI), grain‐filling duration (GFD) and area under spot blotch progress curve per day (AUDPC/day) were examined. The low and high TKWR groups did not differ significantly for TKW, biomass yield, grain yield, HI, days to heading, GFD and AUDPC/day under timely seeding. However, low TKWR lines showed higher TKW, biomass yield, grain yield, HI, and GFD and lower AUDPC/day than the lines with high TKWR under late seeding. Realized heritability estimates for TKWR ranged from 0.68 to 0.85. The findings show that selection for low TKWR could be used as an indirect selection criterion to identify high grain yielding lines under terminal heat stress.

Onion Trait Heritability and Response from Selection

Realized heritability estimates of bolting percentage, pink root and fusarium basal rot severities and incidences, and percentage of single-centered bulbs were estimated for half-sib families of an intermediate-day, open-pollinated onion (Allium cepa L.) population using selection response analysis. Half-sib families were selected based upon an index that equally weighted bolting percentage, pink root and fusarium basal rot severities and incidences, percentage of single-centered bulbs, and bulb quality. Families were subjected to one cycle of half-sib family recurrent selection. Pink root and fusarium basal rot severity was reduced by 17% and 7%, respectively, with realized heritability estimates of 1.28 and 0.65, respectively. More progress for pink root severity was made than was selected. Disease incidence was reduced by 18% and 12%, respectively, with heritability estimates of 0.65 and 0.60, respectively. Very little progress was made for the percentage of single-centered bulbs and this was reflected in a heritability estimate of 0.17. Selection based upon multiple characters at the same time may reduce the effectiveness of making improvements in a single trait. However even with low to moderate heritability, improvements were made, and suggest that further improvements can be made through selection.

Recurrent Half‐Sib Selection with Testcross Evaluation for Increased Oil Content in Soybean

Protein meal and oil are the two commodities produced from soybean [Glycine max (L.) Merr.] that give the crop its value. Increasing seed concentrations of either or both may add value. Objectives of this study were to investigate the effectiveness of recurrent half‐sib selection for increased seed oil, to evaluate the effect of tester oil content on selection response, and to investigate testcross heterosis and inbreeding depression for seed oil content. A recurrent half–sib selection system was devised for soybean and selection for increased oil content was conducted in a population for seven and three cycles using a high and a low‐oil tester, respectively. The base population was a high‐oil composite with gray pubescence (tt) that was segregating for nuclear genetic ms1 male sterility. In summer, the base population was planted in single plant hills and bordered with the tester (Ms1Ms1TT) in a random mating block in North Carolina. About 100 to 200 random male‐sterile plants with hybrid seeds were harvested. Half‐sib families derived from each male‐sterile plant were then grown in Puerto Rico in winter. At maturity, seeds from tawny plants (tester hybrid) were used to identify half‐sib families with high‐oil content. Corresponding gray plant hybrids from sib matings within the population were bulked to start the next cycle of selection. Random progenies from the base populations and selected progenies from each cycle of selection were evaluated in a replicated field experiment at three locations in North Carolina. Cycle × tester hybrids and cycle × cycle sib hybrids were also included in the tests. The results showed that oil content was significantly increased at a rate of 1.1 ± 0.2 g kg−1 cycle−1 in the high‐oil tester populations but not in the low‐oil tester populations. The realized heritability estimate for the high‐oil tester population was 0.12 ± 0.03. Evidence of heterosis indicated that some dominance effects on oil content existed. Dominance effects may affect the evaluation accuracy of the genotypes being tested. A high‐oil tester and high‐oil populations may have many common alleles resulting in less dominance and more additive effects in their hybrids. Consequently, a high‐oil tester can lead to better evaluation and selection precision, compared with a low‐oil tester which could mask additive effects and reduce selection precision.

Divergent Selection for Seedling Tiller Number in Big Bluestem and Switchgrass

Selection at the seedling stage in forage grass breeding would be extremely useful if seedling traits are highly heritable and correlated to desired agronomic traits. Objectives of this study were to determine the response to selection for high shoot weight and divergent selection for seedling tiller number in big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) seedlings and obtain estimates of realized heritability for these traits. Base populations were breeding populations of ‘Pawnee’ big bluestem and ‘Pathfinder’ switchgrass. Divergent selection for single or multiple (three or more) tiller(s) 6 to 8 wk after planting in a greenhouse produced four populations [big bluestem high seedling weight, multiple tiller (BBMT); big bluestem high seedling weight, single tiller (BBST); switchgrass high seedling weight, multiple tiller (SWMT); and switchgrass high seedling weight, single tiller (SWST)], which were planted in isolated polycross nurseries. Seed from polycross nurseries was used to conduct a second cycle of selection. Populations were evaluated in greenhouse studies for fresh weight and tiller number of seedlings. Seedling fresh weight was increased in BBST and SWST Cycle 2 populations, and divergent selection for tiller number resulted in populations significantly different from the base population. Realized heritability estimates for seedling tiller number in big bluestem and switchgrass were 0.26 and 0.23, respectively. The effect of genetic modification of seedling tiller number and shoot weight on establishment under field conditions and on mature plant phenotypes will need to be determined.

LACK OF NONADDITIVE GENETIC EFFECTS ON EARLY FECUNDITY IN DROSOPHILA MELANOGASTER

Fecundity is usually considered as a trait closely connected to fitness and is expected to exhibit substantial nonadditive genetic variation and inbreeding depression. However, two independent experiments, using populations of different geographical origin, indicate that early fecundity in Drosophila melanogaster behaves as a typical additive trait of low heritability. The first experiment involved artificial selection in inbred and non-inbred lines, all of them started from a common base population previously maintained in the laboratory for about 35 generations. The realized heritability estimate was 0.151 ± 0.075 and the inbreeding depression was very small and nonsignificant (0.09 ± 0.09% of the non-inbred mean per 1% increase in inbreeding coefficient). With inbreeding, the observed decrease in the within-line additive genetic variance and the corresponding increase of the between-line variance were very close to their expected values for pure additive gene action. This result is at odds with previous studies showing inbreeding depression and, therefore, directional dominance for the same trait and species. All experiments, however, used laboratory populations, and it is possible that the original genetic architecture of the trait in nature was subsequently altered by the joint action of random drift and adaptation to captivity. Thus, we carried out a second experiment, involving inbreeding without artificial selection in a population recently collected from the wild. In this case we obtained, again, a maximum-likelihood heritability estimate of 0.210 ± 0.027 and very little nonsignificant inbreeding depression (0.06 ± 0.12%). The results suggest that, for fitness-component traits, low levels of additive genetic variance are not necessarily associated with large inbreeding depression or high levels of nonadditive genetic variance.

Two Loci fromLycopersicon hirsutumLA407 Confer Resistance to Strains ofClavibacter michiganensissubsp.michiganensis

ABSTRACT We used molecular markers to identify quantitative trait loci (QTL) that contribute to resistance to bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis. Resistance was first identified as a marker-trait association in an inbred backcross (IBC) population derived from crossing Lycopersicon hirsutum accession (LA407) with L. esculentum. Single-marker QTL analysis suggested that at least two loci originating from L. hirsutum LA407, Rcm 2.0 on chromosome 2 and Rcm 5.1 on chromosome 5, contribute to resistance in replicated trials. Two segregating F(2) populations were developed by crossing resistant inbred backcross lines (IBLs) to elite L. esculentum lines and used to confirm QTL associations detected in the IBC population. In these populations, realized heritability estimates were higher for selection based on maximal disease than for selection based on disease progression. Realized heritability in the population carrying Rcm 2.0 was 0.63 and 0.14, respectively, for each selection criteria. Realized heritability estimates were 0.85 for selection based on maximal disease and 0.37 for selection based on disease progression in a population carrying Rcm 5.1. The disease response of F(3) families selected for resistance suggested that both Rcm 2.0 and Rcm 5.1 confer resistance to bacterial strains in the repetitive sequence-based polymerase chain reaction DNA fingerprint classes A and C. Markers linked to Rcm 2.0 explained up to 56% of the total phenotypic variation for resistance in one population, and markers linked to Rcm 5.1 explained up to 73% of the total phenotypic variation for resistance in a separate population.

Response to within family selection for body weight in Nile tilapia ( Oreochromisniloticus) using a single-trait animal model

Within-family selection for improved growth at 16-weeks was undertaken on Nile tilapia ( Oreochromis niloticus) from 1986 to 1996. Data from 12 generations of selection were analyzed by a single trait Restricted Maximum Likelihood fitting an animal model. The heritability in the base population was estimated as 0.385. A genetic response for body weight was found with an expected mean increase in body weight per generation of 2.2 g or about 12.4%. A realized heritability estimate of 0.14 was obtained based on the regression of mean breeding values on cumulative selection differentials after 12 generations. The inbreeding coefficient was 6.3% after 12 generations with an average inbreeding of 0.525% per generation. The family rotational mating used to propagate the families was effective in keeping the inbreeding rate to a minimum even at high selection intensities. High selection intensities and the relatively high heritability for body weight at 16 weeks resulted in substantial response using the within-family selection method.

Inheritance of root glucosinolate content in canola

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Inheritance of Resistance to Fusarium Wilt in Two Common Bean Races

Fusarium wilt in common bean (Phaseolus vulgaris L.) caused by Fusarium oxysporum Schlechtend. Fr. forma specialis phaseoli Kendrick and Snyder (Fop) occurs worldwide and can result in severe yield loss. Because cultural methods to control disease loss are not completely effective, cultivars with genetic resistance are needed. The objectives of this study were to determine whether genetic control of resistance to Fop race 4 differs between germplasm of races Durango and Mesoamerica of common bean and to estimate heritability of resistance found in race Mesoamerica. Resistant and susceptible lines of races Durango and Mesoamerica were crossed within races to produce F2 and F3 progeny. Reaction to Fop was evaluated using a root‐dip inoculation method and scored using a CIAT disease severity scale from one to nine. F2 populations derived from race Durango parents showed a 3:1 (resistant/susceptible) plant segregation ratio, and F3 progeny tests confirmed that resistance was controlled by a single dominant gene. F2 data from crosses between parents of race Mesoamerica had continuous distributions for reaction to Fop race 4, suggesting polygenic control of resistance. The narrow‐sense heritability estimate derived from midparent–offspring regression of 10 F2 populations derived from Mesoamerican parents was 0.85 ± 0.34, and realized heritability estimates ranged from 0.25 ± 0.19 to 0.60 ± 0.16 among five populations. The heritability estimates as well as the continuous variation in disease severity observed support the hypothesis that resistance to Fop race 4 among parents of race Mesoamerican is polygenic.

Response of Six Alfalfa Populations to Selection under Laboratory Conditions for Germination and Seedling Vigor at Low Temperatures

Alfalfa (Medicago sativa L.) seeded in early spring often germinates and emerges under cold temperatures. We conducted this study to determine if phenotypic recurrent selection improved germination time and seedling growth under cool temperatures in the laboratory. Four selection methods were conducted in the laboratory for two cycles within six commercial alfalfa cultivars: 5454, Alfagraze, Amerigraze 401+Z, Innovator +Z, Magnum IV, and WL252HQ ranging in fall dormancy class from two to four. Cycles 0, 1, and 2 were evaluated in controlled environmental chambers. Two cycles of selection for rapid germination at 5°C decreased germination time (GT) by 29%. Response to selection was greatest in the first cycle. Two cycles of selection for high seedling vigor increased seedling height (SH) after 45 d at 10°C by 15%. In some cultivars, selection for high seedling vigor was effective at increasing SH in the laboratory and further increases may be expected. Selection for high seedling vigor increased GT, indicating an association between these traits under laboratory conditions. The mean realized heritability estimates were 0.49 for GT and 0.18 for SH. Selection for both early germination and high seedling vigor resulted in an average decrease in GT of 29% with no effect on SH after two cycles, but combined selection against both traits increased GT by 162% and decreased SH by 18%. Laboratory selection for decreased GT and increased SH under low temperatures can be successful, but the amount of improvement is population dependant.