Heritability estimates and response to selection for the pungency and single center traits in onion

Summary Heritabilities of the pungency and single center traits were estimated in onion breeding populations using selection response and half-sib family analyses. Pungency was determined indirectly by measuring enzymatically produced pyruvic acid in individual bulbs. After one generation of selection, pungency was lowered by 8.1% and 8.9% in the populations 90-61-1 and 89-69-8, respectively, and realized heritabilities of 0.21 and 0.51 were estimated.Selection had no effect in lowering the pungency of population 90–62. Heritability estimates calculated through half-sib progeny analysis were 0.53, 0.48, and 0.25 for pungency in the populations 90-61-1, 90–62 and 89-69-8, respectively. The number of single centered onions was increased by 19% and 22% in populations 90–62 and 89-69-8, respectively, after one generation of selection, and the realized heritability estimates were 0.37 and 0.34, respectively.     

Climatic adaptation in subterranean clover populations

Summary Long-term persistence and, hence, agronomic success as a pasture of the annual species subterranean clover depend primarily on seed yield and seed survival over seasons. In natural populations, plant characteristics influencing seed setting and formation of seed reserves in the soil are expected to be adjusted to the prevailing environmental conditions of the sites of origin. Knowledge on plant/environment relationships may provide information on adaptive strategies of persistence, and guidelines for selecting adapted varieties to specific conditions. On pure lines from a number of populations such relationships were assessed for flowering time, seed yield, burr fertility, individual seed weight, initial hardseededness, and rate of hardseededness breakdown over summer. Flowering time decreased on decreasing annual rainfall, i.e., on shortening the growing season, as adaptive response to the need of producing adequate seed before the onset of the dry season. Individual seed weight decreased on decreasing rainfall, and increasing temperatures. Hard-seed maintenance over summer was higher in populations from hot and dry environments, where the marked effect of temperature on hardseededness breakdown exerts a strong selective pressure. Within-population variation, assessed on flowering time, was particularly wide, with early genotypes occurring even in populations from long-season environments. The adaptive relevance of maintaining high levels of within-population polymorphism to cope with unpredictable climatic fluctuations is discussed. Number of constituent lines as a measure of the population structure, and intra-population variation were both influenced by altitude and rainfall, tending to decrease as the climatic selective pressure becomes severe, under both low-rainfall, hot conditions and high-elevation, cold-prone environments.     

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.     

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.     

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.     

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.     

Evolution over 16 years in a bulk-hybrid population of subterranean clover (<Emphasis Type="Italic">Trifolium subterraneum</Emphasis> L.) at two contrasting sites in south-western Australia

Evolution was measured over 16 years in a self-regenerating, bulk-hybrid subterranean clover population, consisting of F ₂ seed from 253 crosses, sown at Nabawa and Mt Barker, short and long growing season sites, respectively, in south-western Australia. Seed bank samples harvested annually were grown in a common garden. Experiment 1 measured flowering time in plants from each year, while Experiment 2 measured 26 variables in the populations 3 and 16 years after sowing, in comparison with the ancestral population. Changes in population means were observed in 20 characters and variability declined in 11 characters at one or both sites, with much of this occurring within the first three years. Natural selection at Nabawa favoured early flowering of long duration, thick peduncles, high harvest index and high hardseededness. At Mt Barker it favoured late flowering of short duration, large leaves and long, thick petioles at flowering, thick stems with long internodes, long, thin peduncles with a high burial angle, large plants at maturity, low hardseededness and high biochanin A and total isoflavone contents. High seed production capacity, with high seed weight and seeds per burr, was important at both sites. The use of bulk-hybrid populations is demonstrated as a low-input means of breeding and selecting well-adapted subterranean clovers.

A model describing the flowering of single plants, and the heritability of flowering traits of Dimorphotheca pluvialis

In the development of new crops such as Dimorphoteca pluvialis (L.) Moench, improvement of flowering synchronisation is an important breeding objective. The flowering of single plants of Dimorphotheca pluvialis could be described by a logistic curve obtained by the regression of cumulative number of open flowers on time. The curve is characterised by three parameters, corresponding with the total number of flowers produced by the plant, the rate of flowering development and the day at which peak bloom is reached. From these parameters two other characteristics were derived, i.e., onset of flowering and duration of flowering. The use of the flowering model for selection for improved flowering synchronisation is discussed. Heritabilities of flowering traits were estimated using parent-offspring regression and variance components analyses. Onset of flowering and date of peak bloom showed high (>0.69), and total number of flowers moderate to high (0.30–0.90) heritability values, indicating that for these traits considerable progress may be expected from mass selection, particularly in the early selection generations. Duration of flowering showed low to moderate values (0.25–0.45), and methods other than mass selection (e.g. family selection) should be considered. Determination of phenotypic and genetic correlations revealed only an additive genetic correlation between date of peak bloom and duration of flowering (r _A = 0.80 and 0.69 for 1993 and 1994, respectively), suggesting the possibility of indirect selection for curtailed duration of flowering by means of selection against late date of peak bloom. Duration of flowering, total number of flowers and onset of flowering were not correlated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analyses of phenological traits of pistachio (Pistacia vera L.)

Heritability of flowering and leafing date of pistachio (Pistacia vera L.) were estimated based on half-sib family and parent-offspring regression analyses. Narrow sense heritabilities of flowering date ranged from 0.68 to 0.88 based on half-sib analyses and from 0.89 to 0.95 based on parent-offspring regression analyses. The narrow sense heritability of leafing date was 0.75 based on half-sib analyses and 0.60 from parent-offspring regression analysis. First leafing date was highly correlated with flowering date (r =0.59–0.78), suggesting that first leafing date could be used to select for flowering date in seedlings long before the onset off lowering. This revised version was published online in July 2006 with corrections to the Cover Date.     

Responses to divergent selection for adventitious root growth in red clover (Trifolium pratense L.)

Summary Red clover (Trifolium pratense L.) persistence is improved by the growth of adventitious roots from the crown. The effect of one cycle of divergent phenotypic selection for adventitious roots in red clover was evaluated and root and shoot traits including degree of flowering habit correlated. Three classes of single-cross progenies were produced by crossing plants within and between the high and low root selections. Parents and progeny were grown as spaced plants. Adventitious root score and volume were significantly correlated (p<0.05); however they generally had low or nonsignificant correlations with other variables. A significant correlation (r=-0.36, p<0.01) was found between adventitious root score and flowering score (growth type) in 1988 but not in 1989. Significant variation was found among the three classes of single-cross progeny for adventitious root score and crown diameter. The effect of progeny class on score of adventitious roots was not linear, suggesting dominance effects for the absence of adventitious roots may have been present. A narrow-sense heritability estimate of 0.30 was found by midparent offspring regression of the adventitious root score. This low heritability value implies that successful selection would require progeny testing.     

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.     

Heritability of oil content and the onset of flowering in a population of Dimorphotheca pluvialis

To develop efficient breeding strategies for the improvement of oil content and onset of flowering in Dimorphotheca pluvialis, narrow-sense heritabilities of these characters were estimated. Forty plant progenies were tested in 2 years and heritabilities were estimated from parent-offspring regression as well as from half-sib family variance components analyses. For oil content, the heritabilities estimated by means of parent-offspring regression were 0.36 and 0.33 for 1993 and 1994, respectively. The heritabilities obtained from the variance components analyses were 0.41 and 0.23 for the two years. Heritability estimates for onset of flowering showed more variation. From parent-offspring regression, the heritabilities were 0.72 and 0.37, and from variance component analysis the estimates were 0.53 and 0.19 for 1993 and 1994, respectively. The obtained heritability values and realized responses suggest that particularly in early selection generations, even with mass selection, considerable progress can be expected. Since correlation studies revealed neither phenotypic nor genotypic correlation between oil content and onset of flowering, selection for both characters can be undertaken independently.     

Heritability and correlations among traits in four-way soybean crosses

Recurrent selection programs can use several crossing arrangements to synthesize basic populations for breeding purposes. This study evaluated heritability and correlations among traits in forty-five populations of F_2[4] and F_2:3[4] generations obtained throughout four-way crosses [4] between two dialells among ten semi-late and ten late maturity soybean (Glycine max L. Merrill) genotypes. The generation advance was made by the TSHD (Thinned Single Hill Descent) method and all individual plants were evaluated for the following traits: number of days to flowering (NDF) and maturity (NDM), plant height at flowering (PHF) and maturity (PHM), agronomic value (AV) and seed yield (YLD). Four-way crosses associated with TSHD method provided high genetic variability in the populations with little or no reduction from F_2[4] to F_2:3[4]. The ‘narrow sense’ heritability estimated using correlations between F_2[4] and F_2:3[4] plants was lower than but closely related to broad-sense estimates. The populations 21(IAC-4 × IAC-9) × (GO79-1039 × Paranagoiana) and 23 (IAC-4 × Santa Rosa) × (GO79-1039 × Tropical) were the most productive with high variability in F_2[4] and/or F_2:3[4] generations. Genotypic correlations measured were generally high, positive and consistent for the two generations except for those related to AV and YLD. These results indicate that the use of four-way crosses can be an efficient method to increase the genetic base of populations for recurrent selection or cultivar development. Significant AV × YLD correlations indicated visual selection can be used as additional selection criteria for improving populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Interactions between different genotypic tissues in citrus graft chimeras

The heritability of tolerance of wheat F₃ lines to competition from annual ryegrass (Lolium rigidum), and its relationship to morphological traits, were determined using crosses between wheat cultivars with good and poor competitive ability. Forty F₂-derived F₃ lines from a cross between two late flowering varieties (Machete × Spear) and 40 from a cross between early flowering varieties (Wilgoyne × Gutha) were grown in the field with and without annual ryegrass. There was significant genetic variation between lines within each of the two populations in a number of aspects of plant growth and development, including yield in monoculture. The estimates of heritability for % yield loss due to competition were 0.25 and 0.57 in the two crosses respectively, indicating that selection for high tolerance to competition in the F₃ generation or later should be effective. Fairly strong relationships between height and % yield loss and between leaf length and % yield loss suggest that these may be useful auxiliary traits when selecting for low % yield loss. However, differences between crosses in the magnitude and sign of genetic and phenotypic correlation between traits indicate that competitive ability is a complex character influenced by many factors. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analyses of agronomic traits in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.)

The consumption of products made from Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) has increased in recent years in Japan. Increased consumer demand has led to recognition of the need for early varieties of this crop with high and stable yields. In order to accomplish this, more information is needed on the genetic mechanisms affecting earliness and yield. We conducted genetic analysis of 3 agronomic traits (days to flowering, plant height and total seed weight per plant) to segregate F₂ and F₃ populations derived from a cross between Tartary buckwheat cultivars ‘Hokuriku No. 4’ and ‘Ishisoba’. Broad-sense heritability estimates for days to flowering, plant height and total seed weight were 0.70, 0.62 and 0.75, respectively, in F₃ population. Narrow-sense heritability for total seed weight (0.51) was highest, followed by heritability for days to flowering (0.37), with heritability for plant height (0.26) lowest. Later flowering was associated with increased plant height and higher yields. From the F₄ generation, we identified twelve candidate plants with earlier maturity and reduced plant height compared to ‘Hokuriku No. 4’, but almost the same total seed weight. These results suggest that hybridization breeding using the single seed descent (SSD) method is an effective approach for improving agronomic characteristics of Tartary buckwheat.     

玉米花期性状的全基因组关联分析

花期性状是玉米的重要性状,与熟期、散粉结实率和产量关系密切,对玉米品种选育至关重要。为探究玉米花期性状的遗传基础,本研究以248份遗传多样性丰富的玉米自交系作为关联群体,通过2017年和2018年在河北保定和辛集的田间试验调查抽雄期、散粉期、吐丝期和散粉吐丝间隔期4个花期相关性状,利用分布于全基因组的83057个SNP标记进行关联分析。结果表明,4个花期相关性状的基因型、年份、地点、基因型与地点的互作、基因型与年份的互作均达到极显著水平;抽雄期、散粉期、吐丝期的遗传率分别为71.77%、71.27%、73.93%,并且两两性状间呈极显著正相关,散粉吐丝间隔期遗传率为62.50%,仅与吐丝期呈极显著正相关;4个花期性状共检测到18个SNPs-性状关联(共涉及16个SNP位点),单个位点的表型贡献率范围为5.46%~28.36%,仅1个位点在不同性状中检测到;筛选到81个候选基因,其中36个在GO分析中具有功能注释。潜在候选基因GRMZM5G877647编码early flowering 4蛋白,参与光周期的调节;GRMZM2G173630编码类赤霉素受体蛋白参与植物激素信号转导;GRMZM2G001139、GRMZM2G375707编码与花器官建成的MADS转录因子。这些潜在候选基因为解析玉米花期性状遗传基础和分子辅助选择育种提供参考。     

Number of involved genes and heritability of clover rot (Sclerotinia trifoliorum) resistance in red clover (Trifolium pratense)

European red clover (Trifolium pratense) crops are challenged by clover rot, a devastating disease caused by Sclerotinia trifoliorum or, in some cases by S. sclerotiorum. No completely resistant cultivars are available and resistance breeding is hampered by the lack of knowledge on the number of involved resistance genes and the heritability of clover rot resistance. In this study, we estimated the number of major genes contributing to clover rot resistance by analysing 15 F₁ progeny populations from pair crosses between ramets of resistant and susceptible genotypes. Parent plants were chosen from diverse, diploid populations, including wild material, landraces and cultivars. Young progeny plants were inoculated with ascospores, evaluated phenotypically and the segregation of disease scores was studied. Our results indicated that clover rot resistance may be conferred by three major effect genes, although segregation patterns suggested that there may be numerous minor effect genes involved as well. No proof was found for a maternal inheritance of clover rot resistance. To get insight in the heritability of clover rot resistance, we applied divergent selection by our high-throughput bio-test on an experimental diploid population: the original population (70.5 %), the first generation after selection for susceptibility (79.2 %) and the first generation after selection for resistance (62.3 %) differed significantly in susceptibility (p < 0.001). The second generation after selection for resistance (60.0 %) was not more resistant than the first generation after selection for resistance. In the first generation of selection the heritability (h²) was on average 0.34. In the second generation of selection h² was 0.07. These findings have important implications for resistance breeding.     

Estimates of genetic variability and heritability for vegetative and reproductive characters of kiwifruit (Actinidia deliciosa)

The results of this study indicated a great deal of genetic variation in a number of characters of horticultural interest in kiwifruit seedling populations, and therefore, a potential to improve kiwifruit by vine selection. High narrow sense heritability was shown for pedicel length(0.62) and flowering duration (0.50) in male vines, and pedicel length (0.67),floral shoot percentage (0.54), leaf length-width ratio (0.64), fruit elongation (0.64) and fruit weight (0.52) in female vines. For these traits, selection of superior seedlings should lead to rapid genetic improvement in these populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Leaf appearance of annual clovers responds to photoperiod at emergence

Leaf appearance rate and time to canopy expansion of four annual clover species (arrowleaf, balansa, gland and Persian) were quantified in field and controlled environment studies. Crops sown in autumn, which experienced shortening daylengths at emergence, had a slower rate of leaf production and consequently took a longer time to initiate branching, than spring-sown crops. When autumn-sown ‘Bolta’ balansa clover emerged on the shortest day in winter (21 June), the rate of leaf appearance was lengthened by 4 °C d/leaf/h. When the same species emerged after the shortest day, into an increasing photoperiod, the phyllochron was shortened by 5 °C d/leaf/h. This influence of photoperiod on the phyllochron consequently altered the time to axillary leaf production (branching). Throughout all sowing dates, phyllochron was the fastest for ‘Prima’ gland (33–91 °C d/leaf) and slowest for ‘Cefalu’ arrowleaf (53–116 °C d/leaf) clovers. ‘Bolta’ balansa was 44–82 °C d/leaf and ‘Mihi’ Persian 61–93 °C d/leaf. The response of phyllochron to photoperiod suggests these annual clovers should be sown in late summer or early autumn to initiate axillary leaf production as soon as possible to ensure maximize dry matter for early spring.