Genetic variation, heritability and progeny testing in meadow bromegrass

Meadow bromegrass is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it a major grass species for pasturing beef animals in this region. Because relatively little breeding work has been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate genetic parameters and assess breeding methodologies for meadow bromegrass. Forty half‐sib (polycross and open‐pollinated) and full‐sib (selfed) progenies were evaluated for dry matter and seed yield, fertility index, harvest index, plant height, plant spread, crude protein, neutral detergent fibre and acid detergent fibre. Genetic variation for seed yield, harvest index, and plant height was significant in the open‐pollinated and selfed tests. Genetic variation estimates for dry matter yield were negative (polycross), not significant (open‐pollinated), or significant (selfed). Estimates of genetic variation for quality traits were not significant, except for acid detergent fibre (selfed). Correlations among characters indicated that it is possible to simultaneously improve seed and forage yield. Rankings of progenies by the half‐sib tests for forage and seed yield were not altered by the use of the synthetic parental value (SV_i), which includes information from selfed progeny. The polycross progeny test did not discriminate parents as well as the open‐pollinated and selfed tests; this may have been a result of non‐random pollination in the polycross. Correlation among the progeny tests, showed that open‐pollinated and selfed progeny tests agreed for all characters, except for harvest index, while correlation between polycross and selfed tests were significant for six characters but not dry matter yield, and acid and neutral detergent fibres. The most dissimilar tests were polycross and open‐pollinated, with significant correlations found only for fertility index, height, spread and neutral detergent fibre. It was concluded that there was significant variation and moderate heritability for most traits in the meadow bromegrass populations evaluated, and that the open‐pollinated progeny test is the method of choice for selecting parents for synthetics of this species.     

Condensed tannins in birdsfoot trefoil: Genetic relationships with forage yield and quality in NC-83 germplasm

Summary Genetic relationships of condensed tannins (CT) with other forage quality parameters have not been adequately studied in birdsfoot trefoil (Lotus corniculatus L.). The objectives were to bidirectionally select for CT concentration in birdsfoot trefoil to determine selection response and to create populations for examination of genetic relationships of CT with forage quality parameters, principally lignin. High-and low-tannin parental clones were selected from NC-83 birdsfoot trefoil germplasm and intercrossed to produce Syn₁ populations. Herbage samples, harvested for two years at two locations, were analyzed from high-tannin, low-tannin, and parental populations for CT concentration, herbage yield, and forage quality parameters. The mean condensed tannin concentrations in the high-and low-tannin populations were 69.3±0.8 and 21.1±0.8 g catechin equivalent (CE) kg^-1 dry matter (DM) compared with 36.4±0.8 g CE kg^-1 DM in the parental population. The selection response exhibited a quadratic relationship, with selection for increased CT concentration more effective than for reduced CT concentration. Compared with the parental population, acid detergent lignin (ADL) was higher, and crude protein (CP) and in vitro digestible dry matter (IVDDM) concentrations were lower for the high-tannin population and the converse was true for the low-tannin population. Lignin concentration was positively correlated with CT concentration (r_g=0.66 P0.01).Abbreviations ADF acid detergent fiber - ADL acid detergent lignin - CP crude protein - CT condensed tannins - IVDDM in vitro digestible dry matter - NDF neutral detergent fiber - NIRS near infrared reflectance spectroscopy     

Marker‐assisted parentage analysis reveals high individual selfing rates in tetraploid red clover genotypes selected for seed yield

Seed yield is a major breeding target in tetraploid red clover. We investigated if marker‐assisted parentage analysis can identify progeny plants with two high seed‐yielding parents in tetraploid red clover and if this technique is more advantageous than traditional half‐sib selection. Parentage analysis was successfully performed on the progeny from the 10% highest seed‐yielding genotypes from a second‐cycle family selection trial: 16.0% of progeny were identified with a high seed‐yielding father. However, progeny plants with two high seed‐yielding parents did not produce more seeds than traditionally selected progeny (27.3 g vs. 30.7 g/plant, respectively). The 10% highest seed‐yielding genotypes displayed on average 2% self‐fertilization. Four genotypes were self‐fertile with individual selfing rates up to 20%. Our results discourage the use of marker‐assisted parentage analysis to improve seed yield in tetraploid red clover when the material has been preselected for seed yield. Breeders should be aware that intensive selection for seed yield in tetraploid red clover may inadvertently lead to selection for increased self‐fertility, which may increase inbreeding in the long term.     

Adaptation of forage legume species and cultivars under grazing in two extensive livestock systems in Italy

Legume-based pastures can increase the forage feeding value, the self-provision of protein sources and the sustainability of grazing systems. This 4-year study provided further knowledge on adaptation of forage legume species and cultivars for pasture sowing in extensive livestock systems of inland Italian areas. Three cultivars of lucerne (Medicago sativa L.), two of birdsfoot trefoil (Lotus corniculatus L.) and two of sainfoin (Onobrychis viciifolia Scop.) were evaluated at Casina (northern Apennines) under cattle grazing and at Torricella Sicura (central Apennines) under sheep grazing in farms using rotational grazing with high stocking rates. Semi-erect lucerne and birdsfoot trefoil morphological types, presumably more grazing-tolerant, were compared with erect types. Species showed contrasting adaptive responses, with lucerne at Casina and birdsfoot trefoil at Torricella Sicura being highest ranking for overall dry-matter yield. Lucerne at the former location, and both lucerne and birdsfoot trefoil at the latter one showed the highest final ground cover. The kind of exploitation at Casina (mob-grazing) may have contributed to lower persistence of birdsfoot trefoil. Sainfoin mostly showed potential as a short-term grazing species. Performance of cultivars within species varied with location. Erect cultivars yielded and persisted as well as, or better than, semi-erect cultivars, possibly because of the adoption of rotational grazing and their Italian origin (implying possible better adaptation to local conditions). Erect cultivars of lucerne were specifically adapted to the geographical area in which they were selected. Specific adaptation and targeted intensity of grazing may be the main determinants in the choice of species and cultivars.     

Comparison of two crossing and four selection schemes for yield, yield traits, and slow rusting resistance to leaf rust in wheat

The most important breeding objectives in crop improvement are improving grain yield, grain quality, and resistances to various biotic and abiotic stresses. The objectives of our study were to compare two crossing and four selection schemes for grain yield, yield traits, and slow rusting resistance to leaf rust (Puccinia recondita) based on additive genes in wheat (Triticum aestivum), and to identify the most efficient crossing and selection methodologies in terms of genetic gains and cost efficiency. Segregating populations were derived from 18 simple crosses and the same number of top (three-way) crosses. Half of the crosses were derived from Yecora 70 and the other half from Veery #10 as the common leaf rust susceptible parents. The four selection schemes were: pedigree, modified bulk (F₂ and F₁-top as pedigree, selected lines in F₃, F₄, F₂-top, F₃-top as bulk; and pedigree in F₅ and F₄-top populations), selected bulk (selected plants in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top as bulk; and pedigree in F₅ and F₄-top populations), and nonselected bulk (bulk in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top; and pedigree in F₅ and F₄-top populations). A total of 320 progeny lines, parents and checks were tested for grain yield, other agronomic traits and leaf rust resistance during the 1992/93 and 1993/94 seasons in Ciudad Obregon (Sonora State, Mexico) which represents a typical high yielding irrigated site. The influence of the type of cross and the selection scheme on the mean grain yield and other traits of the progenies was minimal. The selection of parents was the most important feature in imparting yield potential and other favourable agronomic traits. Moreover, the highest yielding lines were distributed equally. Progeny lines derived from Veery #10 crosses had significantly higher mean grain yield compared to those derived from the Yecora 70 crosses. Furthermore, a large proportion of the highest yielding lines also originated from Veery #10 crosses. Mean leaf rust severity of the top cross progenies was lower than that of the simple cross progenies possibly because two parents contributed resistance to top cross progenies. Mean leaf rust severity of the nonselected bulk derivatives was twice that of lines derived from the other three schemes. Selected bulk appears to be the most attractive selection scheme in terms of genetic gains and cost efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analysis of rapeseed self-incompatibility lines reveals significant heterosis of different patterns for yield and oil content traits

Self‐incompatibility is one of the most effective approaches to utilizing heterosis in oilseed rape around the world. To evaluate the heterosis of double low self‐incompatibility, the possibility of combining seed yield and oil content, and the genetic effects of parents on their hybrid progenies, a 2‐year field trial using a 3 × 22 NC II mating design was conducted during the 1999‐2001 growing seasons in Wuhan, China. Significant differences in seed yield per plant and seed oil content were observed among the F1 hybrids and between F1 progenies and their parents. However, the heterosis for seed yield per plant was much greater than that for seed oil content. Mid‐parent heterosis and high‐parent heterosis of seed yield per plant ranged from 5.50 to 64.11% and from –2.81 to 46.02%, while those of seed oil content ranged from –1.55 to 7.44% and –3.61 to 6.55%, respectively. Non‐additive genetic effects were a major mechanism that accounted for the yield heterosis in addition to additive effects. In contrast, seed oil content heterosis was mainly dependent on an additive genetic effect. General combining ability (GCA) determined the stability of hybrid cultivars. In hybrid breeding, parental materials might be selected by the sum of GCAs and variances of special combining abilities (SCAs) of female and male parents for traits affected by both additive and non‐additive effects, and by the sum of GCAs of two parents for traits controlled mainly by additive effects. Primary branches and their siliques were the most important yield traits.     

Improving seed yield in red clover through marker assisted parentage analysis

Red clover (Trifolium pratense L.) is an important perennial forage crop in Europe. Unfortunately, seed production of modern cultivars is often unsatisfactory and breeding progress for higher seed yield is slow. We evaluated whether marker assisted parentage analysis could identify progeny plants with two high seed-yielding parents in a diploid selection trial. Furthermore, we studied if breeding for high seed yield could be speeded up by selecting progeny plants with two high seed-yielding parents, compared to traditional selection on the mother plant only. In this study, 111 genotypes with excellent vegetative traits from a first cycle selection trial were allowed to pollinate each other in isolation. After seed harvest, ten high seed-yielding plants were identified and their seeds were used to grow ten half-sib progeny populations, with 1,121 plants in total. Two multiplex primer sets targeting 18 SSR loci were designed and used to fingerprint parental and progeny plants. Parentage was reliably determined for 1,083 progeny plants: 135 plants were the result of a cross between two high seed-yielding parents. In a 2-year seed yield trial, the seed yield of these 135 progeny plants was compared to that of a control group of 216 progeny plants from the same ten high seed-yielding mother plants but with no selection on the male contribution, as is current practice. Compared to the control group, progeny plants with two high seed-yielding parents had significantly higher seed yields, 23.0 and 75.9 % higher in 2012 and 2013 respectively, and a significantly higher thousand seed weight, 6.6 and 5.7 % higher in 2012 and 2013 respectively. Seed yield was strongly correlated with flower abundance (r = 0.643) and plant volume (r = 0.593 in 2012 and r = 0.509 in 2013) and negatively correlated with susceptibility to mildew (r = ?0.145). We conclude that breeding programs aiming at increasing seed yield in diploid red clover cultivars would strongly benefit from the integration of marker assisted parentage analysis to identify those progeny plants that are the result of a cross between two high seed-yielding plants. This goal cannot be achieved with traditional family selection where only the seed yield of the mother plant is known.     

Analysis of quantitative variability for seed yield and related characters in Lotus corniculatus L. cv. Leo

Summary Quantitative variability for seed yield and six other characters was analysed in Lotus corniculatus L. cv. Leo. The material consisted of 144 polycross progenies and 100 parents.Wide variability existed for all characters. The characters with the greatest variability were seed yield, forage grading and plant height. The polycross progeny test was employed to study the general combining ability of the parents. Highly significant differences existed for all seven characters under study.Parent-offspring genotypic and phenotypic correlations were high and significant for all characters except genotypic correlations for seed yield and seeds per pod. High h² values (broad sense) were obtained for seed size and days to flowering. Traits with moderate to high h² were seed yield (71% in parents, 64% in progenies), plant height, forage grading, and seeds per pod. The character pods per inflorescence had the lowest h².Positive estimates of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabiGaaiaacaqabeaadaqaaqaaaOqaaiqabo8agaqcaK% aaavaabeqaceaaaeaacaqGYaaabaGaaeiraaaaaaa!3A89!\[{\text{\hat \sigma }}\begin{array}{*{20}c} {\text{2}} \\ {\text{D}} \\ \end{array} \] were obtained only for seed size. The ratio of dominance variance to additive variance indicated partial dominance for this character. Except for seed yield, in all other cases these estimates had very high sampling errors. In all cases except pods per inflorescence and seeds per pod high positive estimates of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabiGaaiaacaqabeaadaqaaqaaaOqaaiqbeo8aZzaaja% qbaeqabiqaaaqcaauaaiaaikdaaKaaGeaacaqGbbaaaaaa!3B30!\[\hat \sigma \begin{array}{*{20}c} 2 \\ {\text{A}} \\ \end{array} \] were obtained.The data indicated that it may be possible to simultaneously improve seed yield and maintain forage yield. Seed yield had positive and significant associations with seed size, seeds per pod and pods per inflorescence. The associations of days to flowering with forage grading (negative) and with pods per inflorescence (positive) were also significant.     

Response to selective pressure in early generation progenies of upland cotton (Gossypium hirsutum L.)

Summary Combining high fiber strength with high yield in upland cotton (Gossipium hirsutum L.) was been difficult. The cross combination, 69–120 × 6M-10, was chosen for this study because of the divergence of parents for fiber strength, seeds per boll and crop maturity. Forty F₂ plants were selected in 1974 solely on the basis of visual yield and 20 plants were randomly chosen to serve as a bulk check. The F₃ progenies, the bulk check, the parents and a commercial check were tested in 1975. From these results, five groups were established, consisting of four (10%) progenies each to represent high seed/boll, low seeds/boll, high fiber strength, low fiber strength and high yield in the 1976 test of F₄ progenies. This experiment was conducted to (a) compare the contributions of yield components to lint yield among groups of early generation progenies (F₃ and F₄) and (b) determine the phenotypic correlations between yield and quality attributes. The yield components, bolls/m², seeds/boll, fibers/seed, mean fiber length and micronaire, were included as well as fiber strength.No significant lint yield differences were found among the five groups. Progenies within groups did, however, differ in lint yield. The low and high seeds boll groups gave similar yield and fiber quality results. The low and high fiber strength groups gave similar yield but longer fiber was obtained with the high strength group.Stepwise regression analyses estimates show that the number of bolls produced per unit area, although the major contributor to lint yield for all groups, contributed only 66.9% of the total variation in the progeny group selected for high yield, with fibers/seed, mean fiber length, micronaire and seeds/boll accounting for 13.2%, 8.1%, 6.0%, and 5.8%, respectively. Correlations between the various yield components and fiber strength were low and mainly insignificant, indicating that minor alterations might be made in later generations without serious consequences.Potential gains from second-stage selective pressure upon yield-per-boll components following initial selection for lint yield are discussed.     

Competition among components of synthetic varieties in alfalfa

Summary Eighteen alfalfa polycross progenies were tested for forage and seed yield in pure stand as well as in competition with the mixture of all progenies included in the test. The type of border affected significantly the forage and seed yield of individual progenies in one third of the cases. In most of these cases competition from the mixture resulted in reduction of the yield of individual progenies. There was no correlation between pure stand forage and seed yield, but there was significant positive correlation between forage and seed yield determined under conditions of competition. It is concluded that polycross progenies should be tested in plots bordered by the mixture of all progenies being tested.     

Continued response through seven cycles of recurrent selection for grain yield in oat (Avena sativa L.)

Long-term selection experiments provide germplasm to study the effects of selection in a closed population. Recurrent selection to enhance grain yield in oat has been ongoing at the University of Minnesota since 1968. The objectives of this study were: (i) estimate the GCA and SCA effects for three agronomic traits in the seventh cycle of selection, (ii) assess the effect of the current methods of selection on parental contribution and unselected traits, and (iii) determine the direct and indirect responses to seven cycles of recurrent selection for grain yield. Progeny of the Cycle 6 parents and parents for Cycles 0 through 7 were grown in two separate tests. Grain yield, heading date and plant height were evaluated in each test. Grain yield was increased by 21.7% after seven cycles of selection. Evaluation of Cycle 6 progeny showed that GCA effects were significant for all three traits studied, and SCA effects were significant only for grain yield. Four Cycle 6 parents did not have any progeny selected as Cycle 7 parents. Results from this study indicate that long term recurrent selection has continued to increase grain yield. Alternative selection strategies may be necessary to maintain the genetic variability in this population, particularly when improvement of secondary traits is required. This revised version was published online in August 2006 with corrections to the Cover Date.     

白芥和甘蓝型油菜属间杂种后代种子结构比较

白芥具有很多优良的农艺性状,从白芥和甘蓝型油菜属间体细胞杂种后代中筛选出多个具有黄籽或趋向黄籽性状的株系,利用光学显微镜和电子显微镜技术观察它们种子的结构。回交后代种皮解剖结构与甘蓝型油菜相似,而与白芥相差较远。种皮色素主要分布在栅栏层,甘蓝型油菜和部分后代株系中有色素分布,而白芥和部分黄籽后代株系中没有色素分布。栅栏层在甘蓝型油菜中最厚,在白芥中最薄,而后代介于两者之间。回交后代和甘蓝型油菜种皮表面纹饰为网-穴状,白芥为沟槽状或水疱状。胚子叶细胞面积以白芥最小,甘蓝型油菜最大,后代介于两者之间;而蛋白体面积指数以白芥最大,甘蓝型油菜最小,后代介于两者之间。超微结构观察表明,亲本和后代蛋白体均为球状晶体蛋白体,油体有大、小两种,其大小在亲本和后代间有差异。上述结果表明,回交后代株系种子解剖结构与甘蓝型油菜相近,种皮颜色、色泽深浅和栅栏层厚度,以及胚子叶细胞大小、油体和蛋白体等受亲本白芥的影响而发生变化。     

Random amplified polymorphic DNA variation within and among meadow bromegrass progeny types

Ten meadow bromegrass genotypes tested as half‐sib (polycross, PX; open‐pollinated, OP) and selfed (S₁) progenies were surveyed using random amplified polymorphic DNA. Fourteen primers, which produced 32 markers, were selected to determine the genotypes of 360 individuals from the three progeny tests. Analysis of molecular variance was performed in each progeny test, and genetic distances between genotypes and progeny types were determined. Among genotype genetic variation in half‐sib (PX and OP) progenies was similar. Genetic variation among genotypes for S₁ progenies (30.5%) was about twice that found in the half‐sib progenies. Variation between individual S₁ progenies ranged from 15.7% to 50.1%, while in the half‐sib progenies, the range was 6.9‐24.1%. Based on average distances between progeny types for a given genotype, OP and PX were closer to each other than to the S₁. An analysis of variance of the molecular marker frequency occurrence was performed for 12 plants within each progeny type of each genotype. Marker frequencies, expressed in percentages, ranged from 10.7% to 84.3%. No significant differences were found for genotype and progeny type‐genotype interaction suggesting that all genotypes behave in a similar manner across the different progeny types.     

Identification and inheritance of a partially dominant gene for yellow seed colour in Brassica napus

A yellow‐seeded doubled haploid (DH) line no. 2127‐17, derived from a resynthesized Brassica napus L., was crossed with two black‐seeded Brassica cultivars ‘Quantum’ and ‘Sprint’ of spring type. The inheritance of seed colour was investigated in the F₂, and BC1 populations of the two crosses and also in the DH population derived from the F1 of the cross ‘Quantum’× no. 2127‐17. Seed colour analysis was performed with the colorimeter CR‐300 (Minolta, Japan) together with a visual classification system. The immediate F1 seeds of the reciprocals in the two crosses had the same colour as the self‐pollinated seeds of the respective black‐ and yellow‐seeded female parents, indicating the maternal control of seed colour. The F1 plants produced yellow‐brown seeds that were darker in colour than the seeds of no. 2127‐17, indicating the partial dominance of yellow seed over black. In the segregating BC1 progenies of the two crosses, the frequencies of the black‐ and yellow‐seeded plants fit well with a 1 : 1 ratio. In the cross with ‘Quantum’, the frequencies of yellow‐seeded and black‐seeded plants fit with a 13 : 3 ratio in the F₂ progeny, and with a 3 : 1 ratio in the DH progeny. However, a 49 : 15 segregation ratio was observed for the yellow‐seeded and black‐seeded plants in the F₂ progeny of the cross with ‘Sprint’. It was postulated from these results that seed colour was controlled by three pairs of genes. A dominant yellow‐seeded gene (Y) was identified in no. 2127‐17 that had epistatic effects on the two independent dominant black‐seeded genes (B and C), thereby inhibiting the biosynthesis of seed coat pigments.     

Evaluation of Potato Hybrids Obtained from Tetraploid-Diploid Crosses I. Parent-Offspring Relationships

A total of 45 tetraploid-diploid (4x—2x) hybrid progenies were obtained by crossing each of ten diploid parents as males to each of five tetraploid parents. A relatively low degree of determination (R²) of both 4x and 2x parents on the performance of their 4x—2x hybrid progenies was found for all six traits studied. This implies that test crossing and subsequent progeny analysis is necessary before such parents can be used in a breeding program. Since marketable yield was found to have a higher predictability than total yield, it is the preferred yield trait to be measured. Diploids which produce 2n gametes via FDR usually give rise to 4x progenies with a greater amount of heterosis than similar progenies derived from diploids which produce 2n gametes via SDR, although such heterosis is not necessarily expressed in terms of marketable yield.     

Unravelling the inheritance,QST and reproductive phenology attributes of the tetraploid tropical grass Brachiaria ruziziensis (Germain et Evrard)

The autotetraploid forage Congo signal grass (Brachiaria ruziziensis) is an important component in the Brachiaria breeding programme. As with other tropical forage grass species, the association between flowering and seed yield components, the mode of inheritance and the effects of population structure on phenotypic breeding are lacking. Seventeen characteristics evaluated in 59 half‐sib progeny of seven subpopulations were analysed using a mixed model methodology. According to the commonality analysis, the total seed yield (0.67) and number of days to flowering (0.22) had a greater influence on the filled‐seed yield. The flowering synchrony, total number of panicles, filled‐seed yield, green matter yield and dry matter yield presented statistically significant additive genetic variance between and within the subpopulations. The Q_ST estimates ranged from 0.09 for the flowering synchrony index to 0.31 for the filled‐seed yield. The effects of population structure and its use in breeding programmes are further discussed.     

Effect of plant density on selection for seed yield in two population types of Phaseolus vulgaris L.

Summary Pedigree selection for seed yield, using early generation yield tests, was practiced from the F₂ to F₇ in two populations of common bean (Phaseolus vulgaris L.) in three plant densities: 66, 133, and 266 thousand plants ha^-1 at CIAT-Palmira, Colombia. The six highest yielding lines selected from each plant-density, along with 13 parents, were evaluated in a 7×7 lattice design with three replications at the three densities utilized for selection, and at 399,000 plants ha^-1 in 1988 and 1989.Based on the mean performance of selected lines and the mean of the parents, selection for seed yield was effective in all densities in both populations. However, none of the lines selected from the population within the race Mesoamerica (TC 4673) significantly outyielded their best parent under any plant density. The highest yielding lines selected from the interracial population (TR 4635) outyielded their best parent irrespective of the plant-density used for selection. The highest yielding line originated from the highest density used for selection. Low density was neither good for selection nor for evaluation and identification of high-yielding cultivars of common bean. There was no significant difference between the mean yield of lines selected at the intermediate and high population densities. The effects of plant density, year, and their interactions were significant for seed yield.     

Levels of self-incompatibility in wallflower,Cheiranthus cheiri L.

Summary Approximately 1000 plants from 30 wallflower cultivars were selfpollinated in the open flower and bud stage. Only a very small number of plants failed to set seed and the averages ranged from 3.3 to 11.0 seeds per siliqua. Cultivars with mixed colours appeared to show most self-incompatibility and it is suggested that they form un-evolved populations in terms of the incompatibility system by comparison with their related single-colour cultivars.S1 progenies tended to remain at the same self-incompatibility level as their parents although some segregation occurred with approximately the same number of plants from low to high self-incompatibility and vice-versa.S1 progenies showed no apparent inbreeding depression, as is the case also for their descendants, but there was a tendency for progeny heterogeneity to be associated with high parental self-incompatibility while homogeneous inbreds were most often derived from more self-compatible parents.     

Heritabilities of nutritive quality factors and interrelationships with yield in selected progenies of tall fescue

Nine polycross (PX) and nine different self (S₁) progenies were randomly chosen from 43 selected tall fescue genotypes and evaluated for in vitro digestible organic matter (IVDOM), crude protein, neutral detergent fibre, acid detergent fibre and acid detergent lignin of whole plants, leaf blades and stems (stem plus leaf sheath) at each of four harvest dates in 1991 and 1992. Significant variation for all whole‐plant and leaf quality traits occurred among the PX progenies at the May harvest. Variation among S₁ progenies was significant for almost all of the stem traits. Genetic variance components for both progeny groups were significant for almost all of the traits, confirming the presence of additive genetic variation. Heritability estimates on a progeny‐mean basis ranged from medium to high for almost all the traits of the whole‐plant and the leaf and stem fractions. The results suggest that spring would be the time at which direct selection for high IVDOM or low fibre content would be successful and that selection for leaf or stem quality traits improves whole‐plant quality. Selection for quality traits in the summer or in the autumn would be difficult since no significant genetic variability was found.     

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.