Breeding value of base populations derived from 'contiguous' clusters in perennial ryegrass

Five broad-based breeding populations were produced by polycrossing natural populations sampled in five clusters developed by a hierarchical method with a geographic-contiguity constraint. As a result, each of these breeding populations originates from a single region and the populations within a cluster are more likely to share the same alleles with similar frequencies. A single generation of intercrossing would therefore be sufficient to establish a panmixia equilibrium. These populations were tested for dry-matter yield in plots and compared to control cultivars in two locations. There were some trends of specific adaptation related to the geographic origin of populations, which, on average, compared well to controls. Their half-sib families were evaluated as spaced plants in one location. This allowed genetic parameters and expected response to selection to be computed. Three out of five breeding populations appeared to be promising for the development of new, improved synthetic varieties.     

Genetic variability in herbage and seed yield in selected half-sib families of berseem clover, Trifolium alexandrinum L.

Berseem clover Trifolium alexandrinum L. is an annual forage legume commonly grown in pure stands and in grass mixtures in the Medi-terranean basin. Six populations were naturally cross-pollinated in 1990 and 1991 by a half-sib breeding method. In 1992 and 1993. 54 half-sib maternal plants, six original populations, and six advanced populations were field evaluated for forage (short cycle, harvest made at seven or eight inlernodes: long cycle, harvested at flowering) and seed yield (no forage harvest) in experiments at the Forage Crop Institute at Foggia, Italy (typical Mediterranean location). Genetic variability, narrow-sense herilability, genetic and phenotypic correlations among forage and seed yield component trails were investigated. The genetic variance in dry matter among maternal half-sib populations in short cycle was 51% greater than in long cycle. Narrow-sense heritabilily was 35% higher in short cycle than long cycle for dry matter and 26% higher for seed weight than seed yield. The magnitude of the genetic variance components and genetic correlations suggested that selection among plants of maternal half-sib populations would be more effective for improving dry matter in short than in long cycle harvests. The selection applied in the study was not effective for increasing seed yield per se however, the trait may be increased by selecting indirectly for seed weight.     

Breeding two base populations of perennial ryegrass

Summary A program designed to develop two base populations of perennial ryegrass was initiated in 1985 in Galicia. Multitrait mass selection by a base index was practised in two genetic resources groups of wild Galician populations. Plants selected were intercrossed and the two resulting base populations (F and G) were evaluated in two locations at the spaced plant level and in plot trials with the aim of estimating the genetic parameters and the possibilities for future breeding. The two populations did not show significant differences from commercial cultivars. Production characters had low heritabilities (0.01–0.32) in both locations. Seasonal yields had medium to high family heritabilities (0.36–0.73). For the economic traits chosen, the expected genetic advances were important in both populations for summer and autumn growth in Mabegondo and spring and summer-autumn dry matter yield (1^st and 3^rd year) in Puebla de Brollón. Expected genetic advance for early spring growth was 0.62 in population F. In the autumn of 1991 equal numbers of plants, selected at each location by combined family and mass selection from each of these populations, were planted in two polycrosses with the aim of improving the genetic basis and adaptation of these populations.     

Selection for Seed Yield Production of Egyptian Clover (Trifolium alexandrinum L.) C. V. Fahl

Modified mass and family selection for seed yield production of berseem clover (Trifolium alexandrinum L.) c.v. ‘Fahl’ were applied for two generations. Two hundred plants (5 % intensity of selection) were selected for seed yield in the first season, 1985/86. In the second season, 1986/87, selection between and within half-sib families was practiced. In addition, equal parts of seeds from each of the 200 selected plants were bulked to form the C₁ modified mass selection; after establishing, the same procedure was adopted to form the C₂ generation. The cycles 1 and 2 of half-sib families and modified mass selection along with the base population family were evaluated for forage and seed yields. The realized gains from modified mass selection were 6.03 and 9.51 % for fresh forage yield, 5.57 and 10.86 % for protein yield and 13.23 and 16.19 % for seed yield in cycles 1 and 2, respectively, over the base population. The realized gain from family selection in cycle 2 as a percentage of the base population mean amounted to 11.32, 13.35, 17.47 and 3.15% for forage, protein, and seed yield and seed index, respectively. The broad sense heritability, as estimated from the variance components was 89.63, 63.03, and 76.67 % for dry forage, seed yield and seed index, respectively. Although, all these five traits (fresh, dry, protein, and seed yield and seed index) had positive correlation with each other, weak correlations were found between seed yield and forage yields. Furthermore, close associations were found among forage yield traits.     

Effects of high- vs. low-yield environments on selection for increased biomass yield in switchgrass

No information is available on the effects of different biomass yield environments on selection efficiency in switchgrass (Panicum virgatum L.) breeding improvement. This study was conducted to assess the effects of high- and low-biomass yield environments (HYE and LYE, respectively) on recurrent selection for general combining ability (RSGCA) in a lowland population of switchgrass (NL-94). The top 14 of 65 NL-94 C₀ parent plants were selected based on biomass yield of half-sib (HS) progeny tested for one post-establishment year under HYE and LYE conditions. Nine of the 14 C₀ parent plants were the same based on HS performance under HYE and LYE. Selected plants were intercrossed to produce NL-94 HYE and NL-94 LYE C₁ populations. One hundred and twenty-five HS C₁ progeny families (60 NL-94 HYE and 65 NL-94 LYE) were evaluated for biomass yield for 3 years (2002–2004) under HYE and LYE conditions. The HYE produced about 2.5 times higher biomass yields than the LYE in both C₀ and C₁ HS progeny tests. Estimated additive genetic variance and predicted gains from selection (ΔG) were high in the C₁ populations indicating that RSGCA should achieve higher biomass yields. Mean biomass yields of C₁ HS families originating from the LYE protocol were significantly higher than those of families originating from the HYE protocol in both HYE and LYE performance tests, suggesting greater selection response under LYE in the C₀ population. The estimates of narrow-sense heritability ( ) and ΔG from the C₁ populations indicate that positive response to selection for biomass yield is possible in subsequent cycles of selection under either HYE or LYE, with a possible small advantage for HYE.     

Inheritance of conditional dormancy in over-summering buds of Phalaris aquatica L.

Summary The relative ability of the underground buds of a Mediterranean perennial grass species to break dormancy in response to summer rain was compared between individual plants and between half-sib families in two experiments with broadly-based breeding populations under different environmental conditions. Significant genetic variation was found in summer regrowth activity in both experiments. The narrow-sense heritability of the ratio of new to old, dead tillers after summer rain under spaced plant conditions at a relatively cool site was 0.40±0.16. Under sward conditions at a warm site, the narrow-sense heritability of an index of summer regrowth potential on a half-sib family mean basis was 0.36±0.08. Summer regrowth activity was negatively but weakly correlated with flowering time (r_g=–0.22), and strongly positively correlated with early autumn herbage yield (r_g=0.79). Summer regrowth activity was not genetically correlated with seedling size or herbage yield in the second or third growing seasons. These correlations are different in sign or magnitude from those observed in collections of Mediterranean ecotypes from which the breeding populations were derived by crossing to Australian cultivars and recurrent selection for vigour and persistence. The correlations in Mediterranean populations therefore are not due to pleiotropic effects; they can be altered by recombination. Phenotypic variance relative to the population mean was considerable in both experiments, and hence the level of the responsiveness of dormant buds to summer rainfall should be manipulable readily by selection. The possible effects of altered responsiveness on long term survival and productivity in several different environments are discussed.     

Divergent Selection for Heading Date in Barley

Divergent selection for heading time was performed in two F₂ barley population. Five populations were obtained for each cross: F₅ SSD (unselected control), 3E and 3L (from three cycles of selection for earliness or lateness), 2E1L and ZL1E (from two cycles of direct and one of reverse selection). These populations, together with corresponding parents and F₂ generations, were evaluated over two years. The response to selection was 5.6 and 6.5 days inane direction (earlier heading) and 7.7 and 6.7 clays in the other direction (later heading) in the two crosses, respectively. 3E and 3L populations were highly transgressive as compared to their parents. A sizeable amount of genetic variability was still present after two cycles of selection. Heading was probably controlled by a polygenic system with prevailing additive effects and alleles for earliness and earliness somewhat equally distributed in the parents. Selection fur heading time led to significant changes in plant height, yield and kernel weight. Early progenies were higher yielding than lace ones.     

Pedigree selection for Gibberella ear rot resistance in maize

The pedigree method is often used for developing inbred lines in maize (Zea mays L.). This study was conducted to assess the effectiveness of pedigree selection for improving resistance to Gibberella ear rot in four maize populations. Selection was based on the severity of ear rot symptoms after inoculation with macroconidial suspensions of Fusarium graminearum (Schwabe) into the silk channel (for two populations) and into the developing kernels (for two other populations). Samples of the selfed families (S₁ to S₅), recovered from remnant seed from the selection programs, were evaluated for disease resistance during three years, using inoculation and evaluation protocols similar to those used during selection. Among-family selection was effective in both of the populations selected after silk inoculation and in one of the populations selected after kernel inoculation. Responses to selection were more evident in later than in earlier generations for both types of inoculation. Changes in the estimated genetic gain over generations were consistent with changes in the variances among families, which tended to increase in early generations and to decrease in later generations. Selection after kernel inoculation seemed to have been more effective than selection after silk inoculation in developing families with more stable resistance. Based on the results obtained here, it seems that responses to family selection could be accelerated without increasing operational costs by increasing selection intensity in later generations and inoculating fewer plants per family.     

Genetic variation,heritability and correlations of agro-morphological traits in tall fescue (<Emphasis Type="Italic">Festuca arundinacea</Emphasis> Schreb.)

To study the genetic variation, heritability and genetic correlations of some agro-morphological traits in tall fescue, 25 parents from a genetically broad-base germplasm were polycrossed and their respective half-sib families were generated. Clonally propagated parents and their half-sib families were grown as spaced single plants using a randomized complete-block design with three replications, and observed for seven traits in 2006 and 2007. The estimates of broad-sense heritability were moderate to high for the traits studied. Narrow-sense heritability estimates from analyses of progenies and from regression of half-sib (HS) progenies on parents suggested that genetic variation for these traits was largely controlled by additive gene action. Association of dry matter yield (DMY) with plant height, number of fertile shoot, curbs width and spring growth was positive and significant. With the exception of number of days to pollination, correlation coefficients of the traits between the parents and offspring were not significant. Based on parent-offspring regression, genetic gain from selection for DMY was high, demonstrating genetic potential for improving this trait. Overall, there was high genetic variation and moderate heritability for most traits in the tall fescue populations evaluated. In conclusion, to improve herbage yield, selection would be more effective based on forage yield components.     

Multistage selection indices for maximum genetic gain and economic efficiency in red clover

Selection index updating, a method of multistage selection, allows breeders to determine the optimal truncation point of each stage so that the aggregate genetic gain (▵H) or the gain to cost ratio (▵H/C) is maximum. In this study, we demonstrated the use of selection index updating on selection of red clover (Trifolium pratense L.). We determined the optimal selection schemes that optimized the balance between cost saving and lowered genetic gain in multistage selection. A total of 78 red clover half-sib families were evaluated for petiole length (PL), seedling vigor (Vig) measured at the seedling stage, and canopy height and individual plant dry weight recorded on initial growth (CH1 and DW1) and regrowth (CH2 and DW2). Alternative selection schemes with different number of stages, traits, and proportions selected at various stages were examined to maximize either ▵H or ▵H/C. Single stage index selection had a greater predicted genetic gain than multistage selection, but it was also associated with higher costs. Early culling at the seedling stage resulted in significant cost savings and increased gain to cost ratio. The ratio was 9.857 or more with early culling and 3.062 or less without seedling selection. The most efficient selection programs consisted of PL, Vig, DW1, and DW2. Inclusion of CH1 and CH2 into the selection indices did not contribute to the increase of the total genetic gain, nor to the increase of the ratio. This revised version was published online in July 2006 with corrections to the Cover Date.     

中国大菱鲆引进群体三代选育之后的收获体重遗传进展评估

评估了大菱鲆3个世代选育后（G0、G1、G2和G3）收获体重的遗传参数及遗传进展,分析数据来自于4个世代构建的总共590个家系的12980尾个体。G0、G1、G2和G3的收获体重性状估计遗传力分别为0.19±0.08、0.18±0.09、0.51±0.09和0.29±0.16,跨世代的遗传力为0.16±0.03。根据每一世代所有个体和留作亲鱼个体的平均估计育种值计算了选择差,在G0中为45.6 g,在G1中为13.1 g,而在G2代是 -27.9 g,每代平均10.3 g。遗传进展分别为10.2、37.4、0.3 g,分别相当于2.06%、8.76%、0.04%。经过3个世代选育后的收获体重性状的累积遗传进展为10.86%,平均每代3.56%,表明大菱鲆体重性状的选育工作总体上是成功的。     

Effect of the number of intercrosses on grain yield in basic rice synthetic populations

The effect of 0, 1, 2, 3 and 4 intercross cycles using genetic male sterility on the mean yield and genetic variability of the CNA 5 irrigated rice synthetic population was assessed studying 300 S_0:2 (1998/99) and S_0:3 (1999/00) families grown in two locations (Lambari, MG and Goianira, GO). Each intercross was investigated using a 8 × 8 triple lattice design experiment containing 60 families and four control cultivars. Five experiments were carried out per location and generation, totaling 20 experiments. Individual, combined over locations, combined over generations and combined over locations and generations analyses of variance were performed. Linear regression equations were fitted to data of each location and generation as well as, genetic and phenotypic parameters were estimated. An average increase of 3.91% in grain yield was obtained with the increase in the number of intercrosses. However, when genetic gains obtained from selection of the five and ten highest yielding families were considered, negative b estimates were always obtained, suggesting a tendency of gain increase reduction with the increase in the number of intercrosses. This was confirmed by the analysis of the means of the best families, since increases in the number of intercrosses did not result in selection of families with greater mean grain yield. The estimates of the genetic variances and heritabilities did not suggest an increase in genetic variability with the increase in intercross cycles. Therefore, carrying out intercrosses on the base population did not improve the results of the irrigated rice recurrent selection program. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mass selection for seed width in oat populations

Heterogeneous and segregating oat populations subjected to no selection and to mass selection for seed width for five consecutive generations were evaluated for 100-seed weight, heading date and plant height.The mass-selection technique, which consisted of passing the seeds over a screen with 12.7×2.4 mm slots and propagating the seeds too wide to go through the slots, was repeated for five consecutive generations (F₃ through F₇). Comparable unselected populations were grown each year. Remnant seeds from each check and mass-selected population were stored for future studies.In 1963, 500 random seeds from each of the six unselected populations (F₂ through F₇), from each of the five mass-selected populations (F₃ through F₇) and from a pure line were space-planted in the field. In 1964, the progenies from 75 random strains (a strain was the progeny of one spaced plant) from each of the 12 populations were sown in a randomized-block experiment with three replicates. In 1966, the strains from the last (F₇) generation of the unselected and mass-selected lines of descent (75 strains from each) were tested for yield in a 7-replicate randomized block experiment.The mass-selection technique increased the mean 100-seed weight, whereas in the unselected line of descent, the mean 100-seed weight did not change. The mean heading dates became later and the mean plant heights taller with the mass-selection procedure. The mean yield of the final mass-selection population was nine percent higher than that of the comparable unselected population.In spite of the associated changes between 100-seed weight and plant height and heading date in successive generations; the genotypic correlations among strains within populations indicated that these three traits were inherited independently. In advanced generations (F₆ and F₇), the genotypic variances for heading date and 100-seed weight were reduced in both the unselected and mass-selected lines of descent, whereas, for plant height no significant change occurred in either.Journal No. J-5586 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa, Project 1176. In cooperation with the Crops Research Division, Agricultural Research Service. U.S. Department of Agriculture.Professor of Plant Breeding.     

Observed and Predicted Genetic Gains from Single and Multi-Trait Selections Using Three Mating Designs in Pearl Millet*

The objectives of the study were to estimate the genetic components of variance, predict the response to selection and to evaluate observed response to selection using two populations namely, PSB 7 and PSB 3, of pearl millet (Pennisetum americanum [L.] Leeks). The observed response was studied using four methods of selection based on single and multitrait criteria in three types of families, namely S1, half-sib (HS) and full-sib (FS) families. One hundred SI, HS and FS families each were developed in PSB 7 and PSB 3. Plants within a population were pollinated with bulk pollen of other population to develop HS families. Crosses were made between a pair of plants using one plant from each of the two populations to develop PS families. Data were recorded on days to flower, plant height, tiller number, spike length, spike girth, seed yield per plant and spike weight. Additive genetic variance estimates were significant for all traits. The estimates of dominance and additive × location and dominance × location interaction components were not significant, except additive × location component in PSB 7 for seed yield and spike weight. The genotypic component of variance among S1 families and S1 × location interactions were significant except S1 × location interactions in PSB 7 for days to flower, spike length and spike girth. Twenty-four strains were developed by intermating superior families identified on the basis of four selection methods in each of the six types of families. The selection methods were high seed yield (YS) per se; index selection (IS) for high tiller number and long and thick spike; truncation selection (TS) for high yield among the families having days to flower and plant height lower than the population mean: and visual selection (VS) after completion of flowering for good vigour, uniformity in plant height and good inflorescence attributes. YS and IS were found to be superior to TS and VS with respect to observed genetic gains for seed yield. That advance was higher in selection among SI families as compared with FS and HS families. In general, a good agreement was noted between observed and expected responses. Expected genetic gain from FS reciprocal (R) recurrent selection was higher than the average gain from HS-R selection.     

Prediction of indirect selection for seed and forage yield of lucerne based on evaluation under spaced planting

Phenotypic selection under spaced planting is frequently used in forage species. This study aimed to compare the predicted efficiency of direct selection for lucerne seed or forage yield under dense planting with indirect selection based on the same traits or seed yield components evaluated under spaced planting. Sixteen genotypes randomly chosen from a representative sample of locally adapted germplasm were grown for two years as individual clones spaced at 75 cm (density =1.78 plants/m²) and in dense plots formed by one row of four clones spaced at 10 cm (density = 50 plants/m²) using a randomized complete block design with three replications. Indirect selection based on seed yield under spaced planting was just 19% less efficient than direct selection, owing to moderate genetic correlation between plant densities (r_g = 0.66) and somewhat higher broad‐sense heritability under spaced planting than under dense planting. The relative efficiency of indirect selection for seed yield in density based on individual seed yield components under spaced planting ranged from modest to very low and was always below 45%. The efficiency of indirect selection for dry matter yield based on yield response under spaced planting was moderate for total yield (64%) and very low for second‐year yield (32%) relative to direct selection.     

Genetic variation for seed dormancy in Cuphea laminuligera and Cuphea lanceolata

Summary Various Cuphea species are adapted to temperate climates and characterized by caprylic, capric, and lauric acid-rich seed oils. These fatty acids are solely commercially available from palm kernel and coconut oils; thus, there is considerable interest in Cuphea as an alternative source of these fatty acids. Cuphea is a genus of undomesticated species characterized by seed dormancy and seed shedding. Our goal is to eliminate these domestication barriers in a few species with agronomic potential. Our objective was to survey existing Cuphea laminuligera and C. lanceolata germplasm for genetic variation for seed dormancy (germination percentage after a certain seed storage period). Recurrent half-sib family selection was practiced in various open-pollinated and synthetic populations. Half-sib family seed were evaluated for germination percentages at 26° C after various seed storage periods. There was significant genetic variation among families in every population. Additive genetic variance, half-sib family-mean heritability, and expected selection response magnitudes depended on the length of the seed storage period within a given population. Estimates of these parameters were significantly greater for longer seed storage periods within a population. Heritability estimates ranged from 0.00 to 0.79. Expected half-sib family selection responses ranged from 0.0 to 23.9%. Our study demonstrated there is substantial genetic variation for seed dormancy in C. laminuligera and C. lanceolata.     

Heritability estimates and progeny testing of phenotypic selections for soluble solids content in dehydrator onion

Soluble solids comprise most of onion bulb dry mass, and dehydrator onion cultivars are developed from breeding populations that have high dry mass content. Realized and narrow-sense heritability estimates were obtained for the soluble solids content (SSC) trait in two open-pollinated dehydrator onion breeding populations (BP) using response to selection and half-sib family analysis. Parental populations, designated as BP9335-U and BP9243-U, were derived from two-way crosses of lines advanced as open- pollinated (OP) populations to the F7 or F_6 generation, respectively. BP9335-U had one previous selection cycle for increased SSC and BP9243-U had three SSC selection cycles. In these experiments, parental populations were screened again for high SSC, and selected bulbs were intermated to form half-sib progeny groups, designated as BP9335-S and BP9243-S. Mean SSC was increased by 6.6% and a realized heritability estimate of 0.64 was obtained for BP9335-S. Mean SSC was increased by 6.3% and a realized heritability estimate of 0.36 was obtained for BP9243-S. Narrow-sense heritability estimates of 0.58 ±0.05 and 0.30 ±0.03 were obtained for parental populations BP9335-U and BP9243-U, respectively. Narrow-sense heritability estimates of 0.40 ± 0.03 and 0.63 ± 0.23 were obtained for progeny populations derived from selected high-SSC bulbs of these lines (BP9335-S and BP9243-S), respectively, indicating that there is significant additive genetic control of the SSC trait in these populations. Significant differences in half-sib family performance in the advanced groups BP9335-S and BP9243-S demonstrate that progeny testing was effective for evaluating phenotypic selections. This revised version was published online in July 2006 with corrections to the Cover Date.     

小麦轮回选择的初步实践

利用太谷核不育小麦,开展以抗锈和矮秆丰产为主要目标的轮回选择,选择压分别为5.6%和4.7%.抗锈群通过一轮混合选择,条锈病反应型0—1级的抗病株率和严重度25%以下的轻病株率较基础群体分别提高12.5%和5.1%.矮秆丰产群采用两种轮选方案.经两轮选择看出,改良半姐妹法其群体的株高比基础群体明显降低6.2厘米,其余性状有向选择目标集中的趋势;混合选择法其群体除穗粒数外,其余性状进展趋势与上相同.     

Response to early generation selection for grain yield and harvest index in bread wheat (T, aestivum L.)

The availability of a reliable selection criterion for the identification of the most productive genotypes in early generations represents a crucial point in many breeding programs. The findings reported in the literature concerning the effectiveness of early generation testing for grain yield (GY) or harvest index (HI) are contradictory. In this work, we measured the response to selection for GY and HI applied in different generations, from F₂ to F₆ in nine segregating populations previously screened in F₂ by means of visual selection. Genetic variability for HI and GY was found in most of the segregating populations. However, GY of spaced plants in F₆ and F₃ generations was weakly correlated with yield of F₄ and successive generations grown at normal seed density. HI was of limited value as an indicator of yield potential.     

BLUP for genetic evaluation of plants in non-inbred families of annual crops

Best Linear Unbiased Prediction (BLUP) has become the most widely used method for genetic assessment of animal and perennial species, and it is potentially relevant for annual crops. The objective of this study was to assess this method for selection within non-inbred families in recurrent breeding programs. The ‘animal model’ was fitted. The data were expansion volume (EV) and grain yield of plants in recombination plots of two to three selection cycles in the popcorn population Viçosa, with half- and full-sib progenies. The ASReml program was used to perform the analyses. For both EV and yield the breeding values predicted from the additive and additive-dominant models were highly correlated. Multi-generation BLUP was, in general, more accurate than single-generation analysis. These two methods resulted in highly correlated predicted breeding values. The dominance genetic values predicted from the single- and multi-generation analysis were also highly correlated. The pedigree information reduced the percentage of coincidences among the selected individuals relative to phenotypic selection mainly in the population structured in half-sib families. Based on breeding values predicted by BLUP analysis, the most efficient selection procedure was mass selection.