The use of mitochondrial DNA polymorphisms to distinguish commercial cultivars of the broad bean, Vicia faba L.

Summary Restriction fragment length polymorphisms (RFLPs) have been used to detect mitochondrial DNA (mtDNA) variation among 9 commercial cultivars of Vicia faba L. The mitochondrial DNA was initially digested with 8 restriction endonucleases revealing complex banding patterns on ethidium bromide (EtBr) stained gels. However, no RFLPs were visualised from these complex profiles. Southern hybridisation using total digested mtDNA as a probe against mtDNA digested with the same restriction enzymes revealed a limited number of RFLPs which allowed the 9 cultivars to be consistently distinguished into two main cytoplasmic types. Southern hybridisation with 23 random mitochondrial clones covering 56 kb of the mitochondrial genome revealed considerable levels of polymorphisms. Of the 23 clones analysed, 12 detected at least 22 polymorphisms using 3 restriction enzymes among the cultivars analysed. These RFLPs allowed the 9 commercial cultivars analysed in this study to be distinguished into at least 6 separate groups. Most polymorphisms distinguished the cultivars into two main cytoplasmic groups.     

Comparative responses of botanical varieties ofBrassica oleracea L. (brussels sprouts,sprouting broccoli and marrow stem kale) to inbreeding and hybridisation

Summary The effects of inbreeding and hybridisation inBrassica oleracea L. were studied in diallel crosses within four varieties of Brussels sprouts three varieties of sprouting broccoli and one kale variety. In addition to each intra-varietal diallel within the two horticultural brassicas, plants of one of the other varieties were also included so that the first diallel analysis could be compared with an intra-plus-intervarietal analysis.In general it was found that the total harvest yield of cultivars of the two horticultural types was controlled by an additive genetic system while whole plant weight of all three brassicas was subject to gene interaction. Selfing for one generation reduced the mean harvest yield of Brussels sprout and sprouting broccoli by 26 and 3%, respectively, compared with their intravarietal F₁'s, while whole plant weight of Brussels sprouts, sprouting broccoli and marrow-stem kale was reduced by 21, 26 and 44%, respectively.Kale plants exhibited significant correlations of plant height with plant yield in 2 years and it is therefore possible to achieve some improvement in yield by selecting for height alone.It was postulated that in kale the greatest yield increases should be obtained by the production of hybrids, but hybridisation with subsequent selection is probably sufficient to increase the yield of the two horticultural brassicas still further.     

Genetic diversity within commercial populations of watercress (Rorippa nasturtium-aquaticum), and between allied Brassicaceae inferred from RAPD-PCR

Commercial productivity of watercress (Rorippa nasturtium-aquaticum) can be adversely affected by the pathogenic crook-root fungus, Spongospora subterranea f.sp. nasturti, and watercress viruses. As there are no effective control measures for these diseases, attempts have been made to breed varieties resistant to the crook-root pathogen. This work has been hindered by a lack of knowledge of the genetic base of commercial watercress, and the genetic distance between watercress and allied Brassicaceae which have been identified as candidates for hybridisation programmes. We measured the diversity within these two groups using the RAPD-PCR fingerprinting technique and analysed the data by both distance methods and principal co-ordinate analysis. Little genetic diversity was found within commercial watercress populations. However, watercress formed a unique cluster genetically distinct from other Rorippa species, but equidistant to Cardamine species. It was placed closer to Barbarea verna. This revised version was published online in August 2006 with corrections to the Cover Date.     

Use of the gene pools of Triticum turgidum ssp. dicoccoides and Aegilops squarrosa for the breeding of common wheat (T. aestivum), through chromosome-doubled hybrids

Summary Triticum turgidum ssp. dicoccoides (wild emmer wheat, AABB, 2n=28) and Aegilops squarrosa (goat grass, DD, 2n=14) comprise a rich reservoir of valuable genetic material, which could be useful for the breeding of common wheat (T. aestivum, AABBDD, 2n=42). Many accessions of both wild species, most of them selected for resistance to stripe rust, were used to make amphiploids. Two strategies were applied: (1) the production of autopolyploid cytotypes of the wild species, followed by hybridisation, and (2) the production of allotriploid interspecific hybrids, followed by doubling of the number of chromosomes. The first route was unsuccessful because of failure of the crosses between the autopolyploid cytotypes, possibly due to incongruity between the two species and to reduced fertility in the autopolyploid cytotypes. The second route yielded the desired synthetic hexaploids. However, the rate of success of the crosses was low and there were great differences between years, and within years between crosses. Embryo rescue was applied to obtain the primary hybrids (2n=21), which were highly sterile and had on average 0.3 bivalents and 20.4 univalents per pollen mother cell. Various abnormalities were recorded. Doubling of the number of chromosomes sometimes occurred spontaneously or was brought about by colchicine treatment. The large scale of the interspecific hybridisation programme ensured that one-third of the female and one-sixth of the male accessions were represented in the synthetic hexaploids.     

Natural variation within the genus Beta and its possible use for breeding sugar beet: A review

Summary Sugar beet is a relatively young crop, which supposedly has a narrow genetic base. Natural variation occurring in primitive beet varieties and in wild Beta species has been used for breeding sugar beet. This paper reviews information on desirable characteristics in Beta germplasm and the attempts made for the introgression of such characters into commercial breeding material. After an introduction on the availability of germplasm and the possibilities of hybridisation, attention is focussed on the mating system (especially male sterility), on morphological and physiological characteristics, including yield and sugar content, and on resistances to diseases and pests.     

Ryegrass hybridisation: The effect of artificial isolation materials on seed yield and floral environment

Summary A comparison of conventional glassine pollination bags and recently-developed terylene isolation bags for artificial hybridisation of perennial ryegrass (Lolium perenne) is reported.The yield of seed from plants crossed in a glasshouse using glassine bags was low. When terylene bags were used in the glasshouse, for an identical set of crosses, the seed yield was increased five-fold, while with terylene bags used in the open there was a seven-fold increase. In addition, the seed produced in terylene bags was of higher quality than that from glassine bags. The normal practice of removing the flag leaf laminae of the enclosed culms appeared to be largely ineffective in improving the yield or quality of the seed produced.From a comparison of the floral environment within a glassine and a terylene bag being used for artificial hybridisation in the glasshouse, it is concluded that the large difference in seed yield and seed quality between glassine and terylene crossing bags was due to differences in the relative humidity of the air within the bags.The greatly increased seed yield of crosses isolated by terylene bags compared with conventional glassine bags offers new prospects for grass breeding, in that quantities of seed adequate for the assessment of single-cross progenies under simulated sward conditions can be obtained.     

Assessment of drought resistance in 20 accessions of Triticum aestivum and related species I. Total dry matter and grain yield stability

Summary Interspecific hybridisation has been suggested to improve the resistance of crops to biotic and abiotic stresses. To identify sources of resistance to drought which could be used in a breeding programme, an assessment of a large number of wheat species was carried out. The evaluation was based on the estimation of a drought susceptibility index and stability in total dry matter and grain yields of various species grown across a range of soil moisture conditions. On the basis of stability in total dry matter yield, T. aestivum was relatively more drought resistant. However, on the basis of grain yield stability, T. sphaerococcum, T. vavilovii and T. aestivum cv. C 306 exhibited better yield stability and drought resistance than the other species tested. It is suggested that the above species could be utilized as parental material in a hybridisation programme aimed at improving the drought resistance of wheat.     

A study of hybridisation involving the sweet potato and related species

Overwhelming evidence points to an American origin for the sweet potato Ipomoea batatas (L.) Lam. Attempts have been made to identify related diploid species from Mexico, and to use these in hybridisation experiments with I. batatas. The sweet potato is a poor seed setter but abundant bloom occurs in Jamaica very late in the year. Attempts at hybridisation between I. batatas (2n=90) and I. trichocarpa (Elliott) (2n=30) or I. gracilis (2n=30) has been tolerably successful. A very high degree of self-incompatibility was demonstrated in all three species investigated but successful crosses were made using different plants of I. trichocarpa. An investigation of pollen viability showed that in all cases pollen could germinate but pollen tube growth was abnormal in incompatible pollinations. I. trichocarpa hybridised readily with I. batatas when the former was used as female parent. Embryo development in such a cross proceeded slowly, and stopped before cotyledon formation. No viable seeds were obtained. A comparison of embryo development in hybrid and normal seeds brought to light anomalies in development and structure of endosperm and maternal tissue in the hybrid.     

Breeding vandaceous orchids for commercial cut-flowers in Singapore: an overview

Summary Extensive artificial hybridisation among members of some 86 genera of vandaceous orchids within the subtribe Sarcanthinae in Singapore over the past five decades has created many thousands of exotic hybrids. A small number of these are selected for commercial cut-flower production, while others are cultivated as pot-plants. Two classes of intergeneric hybrids are of special commercial importance as export cut-flowers, the bigeneric Aranda (Arachnis x Vanda) and the trigeneric Mokara (Arachnis x Vanda x Ascocentrum) hybrids. Cytogenetic studies of these hybrids in recent years have provided information on the significance of ploidy levels and genomic constitutions on the horticultural performance of cut-flower cultivars, and also on the strategy for effective breeding in vandaceous orchids.     

Construction and characterization of a BAC library for sunflower (Helianthus annuus L.)

A bacterial artificial chromosome (BAC) library was constructed using the sunflower (Helianthus annuus L.) restorer line RHA325, which carries the restorer gene Rf1 and the Pl2-gene conferring resistance to downy mildew. High molecular weight DNA was prepared from nuclei using leaf material from two-week old seedlings. The library was constructed using the HindIII site of pBeloBAC11. The current BAC library comprises 104,736 clones. The insert size of the clones varied between 20 and 270 kb, with an average insert size of 60 kb. The whole 1.9× sunflower BAC library was spotted in duplicate on four high-density filters, each carrying 55,296 clones. The content of organellar DNA, which was estimated by colony hybridisation against the mitochondrial probe coxI and the chloroplast probe rbcL, proved to be less than 0.03 and 0.1%, respectively. BAC pools, allowing PCR-based screening, were made and used to identify positive BAC clones for the markers OP-K13_454, closely linked to the restorer gene Rf1. The PCR-based screening was verified by the results obtained for this marker by colony hybridisation.     

Investigations into the breeding system of cauliflower

In experiments to study the effect of inbreeding, I₁ progenies of summer cauliflower showed a trend towards increase in plant weight over their non-inbred commercial parents. Curd quality, however, showed no significant improvement.As summer cauliflower varieties tended to behave as pure lines, studies were made on F₁'s from crosses between five commercial varieties. The main results of hybridisation were an increase in earliness, and a slight, though significant increase in curd size over the parental varieties. It is suggested that summer cauliflowers have attained a state of homozygous balance, which could be emulated in the autumm and winter types, by selection of self-compatible individuals.     

Breeding perennial ryegrass for agriculture

Summary Perennial ryegrass has become the most widely sown perennial forage grass in temperate regions due to its combination of high digestibility and tolerance of grazing. The primary objectives in breeding for agricultural use are to improve total and seasonal dry matter production over a range of fertiliser inputs, digestibility, persistency, freezing tolerance and drought or heat tolerance. Adequate seed production and resistance to a wide range of diseases and pests is also necessary. Improvements in productivity and persistency so far have been achieved mainly by hybridisation and recurrent selection using the polycross method and by the use of polyploidy. Further improvements in freezing tolerance, drought and heat tolerance and, for some localities, resistance to pests and snow moulds are required to extend the geographic range of the species. Modern cultivars show little improvement in leaf or stem digestibility but a high magnesium variety is now available. Perennial ryegrass breeding is at an early stage and prospects for further progress appear good.     

Breeding against Dutch elm disease adapted to the Mediterranean climate

Breeding for resistance was considered one of the possible ways to limit the damages caused by the epidemics of Dutch elm disease (DED) during the last century. The elm breeding program developed by CNR in Italy was based on the idea that the Mediterranean environment would need its own specific selections. A base broadening of the genetic resources was operated. A base of native elms with a set of good characters to act as parents was bred with different Asian elm species that showed the ability of acclimatization to the different climates in which elms have to be planted. For this aim a large collection of elm species was constituted, followed by hybridisation studies. Progenies were tested for DED resistance. The more resistant clones were planted in trial fields characterised by contrasting Mediterranean climates in order to select the best potential genotypes adapted either to coastal or to mountain environmental conditions. More than 60 clones resistant, fast-growing and showing remarkable aesthetic ornamental characters were obtained.     

Hybridisation within Brassica and allied genera: evaluation of potential for transgene escape

Determining the potential for hybridisation between transgenic crops and their relatives is a major component of risk assessment. Recent assessments of the extent of reproductive compatibility between crops and their relatives draw heavily on existing data from experimental crosses to infer the likelihood of hybridisation and introgression. Since the literature in this area continues to grow at a rapid pace, it is essential that such analyses can be easily updated. We used a database approach to assemble data on reproductive compatibility for eight crop species in Brassica, Raphanus and Sinapis, using data from hand pollination, spontaneous (unassisted) pollination and trials using in vitro techniques (e.g. embryo rescue), incorporating 326 studies and 216 species combinations. We found many reports for major crop species (B. juncea, B. napus, B. oleracea and B. rapa), but fewer for minor crops (B. carinata, B. nigra, Raphanus sativus and Sinapis alba). Many species combinations remain untested, and we highlight these information gaps. While reproductively incompatible species can be discounted as targets for transgene escape, compatible species must be evaluated further in the particular context where transgenic crops are grown. Because the data is retained in a database in a relatively unmodified form, multiple views of the data can be generated; this review represents one possible view of this data. Our approach also allows new data to be easily incorporated into future reanalyses and can be extended to other crop groups, and as such is a useful method of assembling, analysing and sharing data for risk assessment. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interspecific hybrids between forage rape (Brassica napus L.) and turnip (Brassica campestris L. SSP. Rapifera) as alternatives to forage rape. 1. An exploratory study with single pair crosses

Summary The frequency of sesquidiploid hybrids amongst the progeny of single turnip (B. campestris) plants following their isolation, in insect cages, with single rape (B. napus) plants confirms that the self in compatibility system of the former is sufficient to ensure interspecific hybridisation without resorting to hand pollination. The sesquidiploids performed favourably in a small scale yield trial and their possible production as alternatives to true rape is discussed.     

Pollen morphology as fertility predictor in hybrid tea roses

Fertility of hybrid tea roses is often reduced due to their interspecific origin but also to intensive inbreeding. New genotypes used as pollen donors represent an economic risk for a breeding programme, as their influence on seed production is unknown. In this study 11 cut rose genotypes were selected from a company database as high fertile or low fertile male parents, according to the number of seeds per hybridisation. Pollen morphology and in vitro germination of the selected genotypes were characterised. Pollen was either small (mean diameter <30 μm), shrunken, and irregular (abnormal), or large (mean diameter >30 μm), elliptical and crossed by furrows (normal). High correlations were found between the number of seeds produced per hybridisation and the pollen diameter (r = 0.94) or the percentage of normal pollen (r = 0.96). In order to evaluate the predictive power of the models, we conducted regression analyses and performed a validation experiment on genotypes not present in the database and without background information on fertility. Pollen diameter and percentage of normal pollen were characterised and fitted in the regression models for seed set predictions. Validation with an independent dataset gave a good prediction for 83.3% of the data. This indicates that using either the mean pollen diameter or the percentage of normal pollen resulted in effective fertility prediction. This tool could enhance the genetic variability in crossings between hybrid tea roses, thus creating possibilities for less economically risky exploitation of new tetraploid genotypes as male parents.     

Cryopreservation of pollen from two rose cultivars

Summary An investigation was undertaken on the storage characteristics of pollen collected from two English rose cultivars. A rapid decline in viability was observed in pollen stored at +4° C and –20° C, whereas the viability of pollen, stored at ultra-low temperature (–196° C), remained constant. Cryopreserved pollen was shown to retain its ability for fertilisation. The effects of the stage of flower development and anther dehiscence were assessed on both pre-and post-cryopreservation viabilities. Successful long-term storage of pollen will facilitate hybridisation of rose species and cultivars that do not flower synchronously.     

Identification,distribution and effects on agronomic traits of the semi-dwarfing <Emphasis Type="Italic">Rht</Emphasis> alleles in Bulgarian common wheat cultivars

Bulgarian common wheat cultivars released in the period 1925–2003 were studied using the gibberellic acid (GA) test and microsatellite analysis of the Xgwm261 locus on chromosome 2DS to identify the semi-dwarfing (Rht) genes. The old cultivars, isolated through selection from landraces, carried rare alleles (211- and 215-bp) at Xgwm261 locus, and those developed by hybridisation to foreign cultivars, carried the 165- and 174-bp alleles. Forty-two (55.3%) of 76 modern cultivars were GA-responsive. The 192-bp allele, diagnostic for Rht8, was observed in 64 (84.2%) modern cultivars, of which 37 carry Rht8 alone, and 27 possess a combination of Rht8 and a GA-insensitive allele viz. Rht-B1d (17); Rht-D1b (6) and Rht-B1b (4). The 174-bp allele is present in seven cultivars, only one of which is photoperiod-sensitive, and the rest are day-length insensitive. The 203-bp allele was found in six modern cultivars. Cultivars carrying the Rht8 allele are the most widespread and some of them have been cultivated for a long period. Cultivars with the `Saitama 27' allele (Rht-B1d) are the most productive and are second in distribution in the country. The recently observed trend for increasing the proportion of cultivars with GA-insensitive Rht genes is probably due to their combination with the 192-bp allele of Xgwm261 locus tightly linked to the Ppd-D1, to the break of the link between the 174-bp allele and ppd-D1, and to the introduction of other genes influencing flowering time.     

Genetic resources and breeding of Capsicum spp.

Five species of Capsicum have been domesticated in the American tropics, but breeding programs have concentrated on the non-pungent cultivars of C. annuum. Studies of the consequences of human selection during and after domestication support theoretical calculations that there will be significant amounts of genetic diversity within as well as between species. Breeders have only recently begun to exploit this diversity. Multiple resistances are available to several pests and diseases, but have to be transferred from one agronomic or market type of pepper to another. Problems in selecting simultaneously for multigenic resistances and polygenic quality characters may be eased by the development of molecular markers and a molecular linkage map for Capsicum. Ploidy changes (both tetraploidy and haploidy) are relatively easy to induce in Capsicum species. Doubled haploids have proved particularly valuable in the analysis of the genetically complex basis of some resistances to pests and diseases. Barriers to interspecific gene transfer are similar to those found in other genera of Solanaceae: unilateral incompatibility, post-fertilisation abortion, and nucleo-cytoplasmic interactions leading to male sterility or other abnormalities. Information on the occurrence and effects of these barriers should be available if or when breeders need to turn to interspecific hybridisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Single-seed descent, single-pod, and bulk sampling methods for soybean

The single seed descent (SSD) method of inbreeding minimizes the amount of genetic sampling. The single-pod descent (SPD) and bulk methods (BM) produce redundant inbred lines that are descended from either the same F₂ or F₃ plant. However, for soybean [Glycine max (L.) Merr.], the SSD method requires more time to process the seed than the SPD or BM. Our experiment is the first to compare the SSD, SPD and BM by sampling the same population in the field and then evaluating the methods using molecular markers. Our objective was to determine the relative efficiency of the SSD, SPD and BM procedures. We defined unique lines as those lines that were not paired with any other line at a coefficient of similarity (S_xy) level ≥ 0.875, which was an alike-in-state criterion. The efficiency was defined as the number of unique lines developed by each procedure. We genotyped 100 F_4:5 lines from each of the three genetic sampling methods, using 21 polymorphic simple sequence repeat markers. The number of unique lines was the same for all three sampling methods at the 0.05 level of Type I error. Based on our criterion, the three sampling methods are equally efficient. Our conclusions were the opposite of all other previously published reports. Each breeder will have to determine the best method for generation advancement, based on the amount of resources required to harvest and process the seed.