Genetic variation for resistance to low-temperature photoinhibition of photosynthesis in maize (Zea mays L.)

Summary In the partially allogamous faba bean, yield and yield stability can be improved significantly by heterozygosity and heterogeneity. The commercial production of hybrid varieties for the full exploitation of heterosis is still unfeasible. Hence, the breeding of synthetic varieties has repeatedly been recommended. The present study aimed at investigating whether and to what extent effects due to heterozygosity and heterogeneity occur in such varieties, particularly in relation to Syn-generation. A sample of 36 inbred lines (Vicia faba L. minor) was used to generate several entries of different population structure, e.g. blends of inbred lines (=Syn-0), experimental synthetics of generations Syn-1 to Syn-4 and polycross progenies. In 1986 to 1991 these entries were evaluated together with their parental lines grown in pure stands in six series of multi-locational field trials in West Germany. The yield of the synthetics increased with successive Syn-generations and asymptotically approached its maximum by as early as generations Syn-2 or Syn-3. The yield increase was mainly caused by heterozygosity. In two synthetics the yield increase corresponded to about one-half to two-thirds of the mid-parent heterosis. Effects due to heterogeneity were small and mostly non-significant. In one out of three expriments significant effects due to seed source were observed which, however, did not alter the yield increase with successive Syn-generations. Hence, Syn-generations Syn-2 or Syn-3 may be sold to the farmer.     

Analysis of a site x year experiment with timothy polycross progeny

Summary Results from a cooperative breeding programme with timothy for the northern areas of Scandinavia are presented. The main aim of the programme was to identify genotypes for synthetic populations that are high yielding, adapted over the whole area and stable over years. A polycross comprising 12 genotypes from each of five sites within the region was formed. The subsequent 60 half-sib families and four reference varieties were then compared under sward conditions at the same sites. The trials lasted for three years and results for total dry matter yields are presented.Significant differences in yield between lines were found. There were also significant two and three factor interactions between lines, sites and years. A new two-step procedure is presented to select the genotypes to make up a synthetic variety. Firstly, a superiority measure (Q-value) is used to select a group of genotypes that are high yielding and stable over sites and years. Secondly, the GxE part of the Q-value is split into two terms. One measures adaptation to predictable environmental conditions. The other one measures stability to unpredictable changes in the environment. A plot of these two measures provides a tool for discarding unstable or poorly adapted genotypes. The statistical properties of the selection parameters are discussed.     

Factors determining the performance of synthetics in Vicia faba L. 1. Heterogeneity,heterozygosity, and degree of cross-fertilization

Summary The relative performance of synthetic varieties in faba beans (Vicia faba L.) as compared with line varieties is the result of the joint effect of several factors. Factors investigated in the present study were (1) effects of heterogeneity and (2) heterozygosity on agronomic performance, (3) genetic variance for the degree of cross-fertilization among inbred lines and (4) genetic variance among homozygous and heterozygous genotypes for yield. The evaluation was based on multilocational trials in Germany with 36 inbred lines and derived entries with contrasting population structure (levels of heterozygosity and heterogeneity). When inbred lines and F₁-hybrids are included in the same mixture of genotypes, the resulting heterogeneity had a positive effect on yield. Relative mid-parent heterosis for yield was between 33% and 51%. The average degree of cross-fertilization was 53.5%, and its genetic standard deviation was 8.3%. The estimates for genetic standard deviation for yield among inbred lines were between 3.4 q/ha and 5.3 q/ha. The highest yielding synthetic variety is expected to outyield markedly the highest yielding line.     

Yield Stability in Faba Bean,Vicia faba L. 2. Effects of Heterozygosity and Heterogeneity*

In order to evaluate the effects of heterogeneity and heterozygosity on yield stability in faba beans, genotypes were generated with contrasting population structures, differing only in their levels of heterogeneity and heterozygosity. All entries were based on either eight or 36 inbred lines, respectively. The population structures tested consisted of pure stands of the inbred lines (1) and of their F₁,-hybrids (2), blends of the inbred lines (3) and of their F₁ hybrids (4), four-component synthetics in different Syngenerations (5), the open-pollinated source varieties (6) and 36 polycross progenies (7). Five different entry sets (= data sets), each covering several of the seven population structures listed, were grown during 1986 to 1991 in at least four different environments in Western Germany and tested for yield. Stability parameters, i.e., the regression coefficient and deviation from regression (EBERHART and RUSSELL 1966), and the ecovalence (WRICKE 1962), revealed that yield stability of the different population structures was improved by increasing heterozygosity as well as heterogeneity. But the impact of both factors of diversity on yield stability varied between the different data sets. Positive effects of both factors on yield stability seemed to be additively combined in the hybrid blends (data set I). The same proved to be partly true for the four different Syn-generations of the nine synthetics tested. Yield advantage of the different heterozygous variety structures over the homozygous ones in creased with increasing yield level at test sites, as indicated by regression coefficients larger than 1.     

Marker assisted polycross breeding to increase diversity and yield in perennial ryegrass (Lolium perenne L.)

Summary In this study, the application of molecular markers to optimise genetic diversity in a polycross breeding program of perennial ryegrass (Lolium perenne L.) was evaluated. The genetic diversity among 98 potential parental plants from three maturity groups (early, intermediate and late flowering) was investigated using amplified fragment length polymorphism (AFLP) markers. For each maturity group, two polycrosses of six parental plants with contrasting levels of genetic diversity were composed. Average genetic diversity among parents selected for narrow polycrosses was 36% lower than among parents selected for wide polycrosses. Diversity within first generation synthetic progenies (Syn1) was proportional to the diversity within the respective parental polycrosses. However, differences were less pronounced with Syn1 progenies from narrow polycrosses showing 16% reduced diversity when compared to Syn1 progenies from wide polycrosses. Multivariate analyses allowed for a clear separation of the six Syn1 progenies based on AFLP markers and demonstrated their genetic distinctness. Evaluation of dry matter yield, date of ear emergence and stem length of Syn1 and Syn2 progenies showed progenies from wide polycrosses to be constantly higher yielding when compared to progenies from narrow polycrosses. On the other hand, there was no significant difference in variability for the two morphological traits between progenies of narrow- and wide polycrosses. The results presented here provide evidence for an efficient application of molecular markers to select genetically diverse polycross parents which resulted in an average yield increase of 3.8%.     

Comparison of Progeny-Testing Methods in Lolium perenne L.

From 28 genotypes, half-sib families were generated by polycross (PX) and 2 topcrosses (TC). TC-testers were partially inbred cms-lines. Progenies were tested for annual dry matter yield in 3 successive years. The three year average was 80.7, 76.6 and 74.0 dt/ha for TC 1, PX and TC 2, respectively. TC 1 had the highest yielding families and the largest mean in all years. TC 2 revealed the largest range among its families. Genetic variance was highest for TC 2 with 14.02, followed by TC 1 and PX with 12.05 and 10.92. However, genotype × year interaction variance was about 2 and 4 times greater for TC 1 and TC 2 as compared to PX. Genetic correlation between testcross progenies was tightest for PX vs. TC 1 (rg = 0.644⁺⁺), while between the two TC's only rg = 0.307⁺ was observed. Predicted response to selection yielded very similar results for all test-crosses.     

Genetic Structure of Three Open-Pollinated Faba Bean Varieties (Vicia faba L.)*

To study the genetic structure of open-pollinated faba bean varieties, three sets of genotypes were generated from each of the varieties ‘Minica’, ‘Kristall’, and ‘Deiniol’: (1) inbred lines developed by single-seed descent in bee-proof isolation cages, (2) intravanetal and (3) intervarietal F₁-hybrids produced by controlled hand crossing. In 1989 and 1990, a total of 144 entries, including the three open-pollinated source varieties, were grown in single-row plots with two replications at two locations in Western Germany. Performance data of the inbred lines revealed relatively large genotypic variability within each variety, for all the characters studied, which was greater in ‘Deiniol’ and ‘Kristall’ than in ‘Minica’. An average yield heterosis of 20 %, 39 % and 57 %, respectively, was found for the intravarietal hybrids, whereas that of the intervarietal hybrids varied between 70 and 73 %. Compared to the mean yield of the inbred lines the superiority of the open-pollinated source variety was small and not significant in ‘Minica’ (6 %), but it was large and highly significant in ‘Kristall’ (22 %) and ‘Deiniol’ (37 %). The present investigation revealed in faba bean that similar performance levels of open-pollinated varieties may result from either high per se performance under inbreeding with low heterosis values or from lower per se performance but with high heterosis values.     

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.     

Use of isozyme analysis in the breeding of synthetic rapeseed cultivars

Eleven winter rapeseed inbred lines (I₄) were characterized according to isozyme banding patterns from seven polymorphic enzyme systems. All lines could be qualitatively and quantitatively distinguished using two enzyme systems, shikimate dehydrogenase (SDH) and diaphorase (DIA). Genetic distances were calculated among lines and 15 selected two-line hybrids were planted as experimental synthetics in field-trials. Syn-0 populations produced seed yields between 0.4% lower and 12.9% higher than the mean yields of the respective parental lines. Syn-1 seed yields were 11–24.1% higher than the respective parental lines and the yield improvement was positively correlated with the genetic distance between the parental lines. This tendency suggests that genetic distances between cross components, calculated from isozyme polymorphism, can be used in prognosis of yield performance of synthetic rapeseed cultivars. Isozyme analysis was also applied to study fertilization behaviour in line mixtures, and differences among parental lines were observed with regard to the tendency for self-pollination or out-crossing. The partially very high outcrossing rate suggests the possible existence of a self-incompatibility system.     

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.     

Combining ability for beet armyworm, Spodoptera exigua, resistance and horticultural traits of selected Lycopersicon pennellii-derived inbred backcross lines of tomato

Ten selected inbred backcross lines (IBL), from a Lycopersicon esculentum cv.‘Peto 84’×Lycopersicon pennellii IBL population, with resistance to beet armyworm (BAW), Spodoptera exigua, higher fruit mass and fruit yield, were crossed with eight elite cultivated L. esculentum inbred lines in a Design II mating design. Three elite inbreds were also crossed to ‘Peto 84′, the IBL recurrent parent, as a control for combining ability. Field plots of all resulting F₁ progenies and control cultivars were inoculated with BAW eggs and evaluated for resistance to BAW, fruit mass, fruit yield, vine size and maturity at three field locations. Reductions in fruit damage by BAW were found in four of the 10 IBL F₁ progenies. Significant male and female general combining ability (GCA) estimates for BAW resistance were observed, but significant specific combining ability for BAW resistance was not detected. The fruit mass of F₁ hybrids was significantly lower than large-fruited controls, but was not significantly different from elite inbred by ‘Peto 95’F₁ hybrids. Selection based on inbred performance identified IBL with positive GCA for BAW resistance and yields in Design II hybrids. BAW resistance in the 09 selected IBL and IBL- derived F₁ progeny was associated with two undesirable traits, later maturity and larger vine size. Index selection of IBL was more effective at identifying IBL with positive GCA for fruit mass and fruit yield than GCA for BAW resistance.     

Properties of maternal haploid maize plants and potential application to maize breeding

Summary Presented are the results of a two-year study of haploid maize plants in the field. The haploids were produced with the aid of inducer line ZMS. In total, 604 and 1030 haploids were obtained and studied in the first and second years, respectively. Tassels of haploid plants were found to be almost completley sterile. Fertility of ears was studied by pollinating them with the pollen from diploid inbred lines, the cross resulting in almost all of the haploid ears carrying kernels. On average 27.4 kernels per ear of haploid plant were obtained in the first year of study and 26.3 in the second. These gave rise to normal diploid plants. This property allows genotypes selected at the level of haploid plants to be involved in breeding process. Unusual plants were found among haploids, phenotypically resembling homozygous lines. It was assumed that the plants had resulted from spontaneous chromosome doubling in haploids. The results of comparative studies of progenies of unusual plants and inbred lines derived from the same synthetic population are presented.     

东北不同生态条件对大豆杂交后代的选择效应

以５个大豆杂交组合的Ｆ２－Ｆ５代为材料，连续４年在东北三省８个试验点按当地的高产育种目标进行选择，于Ｆ５代每个地点从每一组合中决选出１个高产品系，各地共计决选出４０个优良品系，并在上术８上地点以同一方案进行两年生态试验，以便分析生产条件对大豆杂交后代的选择效应。试验结果表明，在不同生态条件下，各地都选出了适合当地生态条件的生育期类型；在不同肥力条件下，各地都选出了适合当地生态条件的百粒重和抗倒伏性     

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.     

Differential response of Vicia faba L. genotypes to 2, 3, 5-triiodobenzoic acid (TIBA)

Summary Response to application of the growth regulator 2, 3, 5-triiodobenzoic acid (TIBA) was examined in the parents and F₁ progenies of a diallel cross of six inbred lines of Vicia faba. TIBA affected the genotypes differentially but in general gave shorter internodes, reduced apical dominance, increased pod set on the lower nodes and earlier seed maturity.     

Cooperative breeding for the northern marginal areas

Summary A joint breeding project for the northern areas of Scandinavia and Iceland was initiated in 1981 under the auspices of the Nordic Council of Ministers. Initially, efforts concentrated on cooperative trials in which both early and more advanced breeding material was tested at a number of experimental stations in the northern regions. This was followed by a joint breeding programme for timothy with the primary aim of developing varieties that possess broad adaptation to a range of Nordic climates and managements and can be grown throughout the northernmost part of Scandinavia. Each of the five national breeding stations originally provided 12 timothy genotypes for the project giving a total of 60 genotypes. The parental genotypes were compared as spaced plants at all five stations and their polycross progeny were grown under sward conditions at the same sites. On the basis of results obtained from these field trials parent clones have been selected and intercrossed to form synthetic populations.     

Comparison of Progeny-Testing Methods in Lolium perenne L.

From 22 genotypes, selfed (S₁) and testcross progenies were investigated. The latter were generated by i) polycross (PX) and ii) 2 topcrosscs (TC) using cms-inbred lines as a tester. Progenies were tested for annual dry matter yield in 3 successive years, the 3-year average was 76.7 dt/ha for S, and 76.9, 80.1 and 74.5 for PX, TC 1 and TC 2, respectively. Genetic variance was highest for S₁ (20.42), while the average of the 3 tcstcrosses was 12.22. However, the genotype-year interaction variance of S, Was 52.21, being 2–3 times greater than for the 2 topcrosscs. PX progenies were the most stable across years. Predicted response to selection was highest for S₁ (10.4 %). Genetic correlation (r_g) between S₁ and the testcrosses was highest with TC 2 (r_g= 0.5931⁴⁴).     

Plant breeding: past,present and future

Plant breeders can help farmers increase food production by breeding new cultivars better adapted to their chosen farming systems, but these must be capable of providing the necessary plant inputs for the required levels of crop production in 2050. Until 200 years ago the farmers themselves were the plant selectors. Plant domestications, extensive crop dispersions and farmers’ selections produced thousands of locally adapted landraces of cultivated plants. During the twentieth century these were largely replaced by relatively few high yielding cultivars and the natural habitats of many of their wild relatives became endangered. Hence in situ and ex situ conservation, and evaluation and use of plant genetic resources is vital for future plant breeding. The development of scientific breeding from the beginning of the twentieth century was based on understanding the mechanism of inheritance and the mating systems of crop plants. The types of genetically uniform, high yielding cultivars that have been bred from genetically heterogeneous landraces were determined by the mode of reproduction and mating system of the cultivated plant species: inbred line (wheat) and hybrid (rice) cultivars for inbreeding species, hybrid (maize) cultivars for outbreeding species, and clonal (potato) cultivars for vegetatively propagated species. When genetically heterogeneous crops are desired, mixtures of cultivars and synthetic cultivars can be produced. Future progress in crop improvement will come from three complementary approaches: use of hybridization and selection in further conventional breeding, base broadening and introgression; mutation breeding, cisgenesis and gene editing; and genetically modified crops.     

高大韧稻恢复系特恢的选育和应用研究

用明恢63、古154、靖西中稻大粘等三个茎秆比较粗壮、高大的恢复系、农家品种进行杂交、复交,从其后代中选择茎秆粗壮、高大、穗长大的单株与珍珠高粱杂交,杂交后代经过24代的选择,选育出新型恢复系特恢。比较了特恢与明恢63、9311、253、838、桂99、207等恢复系的生物学性状、农艺性状和产量表现。结果表明特恢具有高大韧,与不育系配组杂种优势强大等优良特性。     

Molecular marker variability for southern root-knot nematode resistance in sweetpotato

Summary As organic farming refrains from high and chemical inputs it needs varieties better adapted to organic conditions to improve the yield stability and quality of crops. In order to make genebank accessions more accessible for the utilisation in organic breeding programmes, a participatory research project with farmers was carried out in 2002 and 2003. From the Dutch genebank collection 37 onion accessions, divided into five different groups (according to their market use), were selected and planted at a commercial organic farm. Farmer participation in characterisation and evaluation of the material resulted in including additional plant traits for genebank characterisation as well as new selection criteria for breeding. It also provided researchers insight into how organic farmers evaluate and value certain plant traits. Variation for important properties was found within and between the five groups. To establish base populations, the farmers, in collaboration with the researchers, selected the best genotypes within the five groups of onion accessions. The new base populations may be exploited in order to achieve better-adapted material for organic farming systems.