Crossability and embryo rescue enhancement in wide crosses between wheat and three Agropyron species

Summary Soft winter wheat lines were crossed with Agropyron intermedium, A. elongatum and A. trichophorum using pollen from single plants of Agropyron spp. to pollinate wheat spikes. Not only species but also individual plants within varieties of Agropyron species differed in percent seed set with a wheat genotype. In two arrays of crosses between two phenotypically different plants of A. elongatum and nine wheat lines, one Agropyron plant gave higher seed set (overall=27.1%) than the other (overall=3.7%). The differences were significant in seven of the nine cross combinations. Results are consistent with the hypothesis that these two plants differ in their crossability as pollen parents with wheat, and suggest the possibility of occurrence of crossability genes in wheatgrasses. The success rate of hybrid embryo rescue was higher (87.5%) with cold treatment (4°C) than without cold treatment (75.0%) of excised embryos on culture media. Results underscore the significance of genotype of the alien species for crossing with low crossable wheats, and of the physical factors for improving embryo rescue in wide crosses.Contribution No. 11,825, Purdue Agric. Exp. Stn., West Lafayette, Indiana 47907, USA. The research was supported in part by Public Varieties of Indiana.     

Interspecific Crossability and Inheritance in Pelargonium

Different Pelargonium hybrids are of great importance to horticulture. Breeding; for F₁ hybrid and clonal eultivars is particularly prevalent in Europe, Japan and North America. The results of a great deal of breeding research are scattered throughout different journals and published in several different languages. The aim of this review is to summarize the results of research on interspecific crosses and the inheritance of flower and leaf colour, plant habit, resistance and floret type.     

Crossability between tritordeum and triticale

Seed set over three years in crosses between three tritordeums used as female parents and four triticale lines, showed that there are significant differences in crossability attributable to both parents and that most of these differences are consistent over the three years. When used as the female parent tritordeum line HT67 had an average seed set of 29.62%, tritordeum line HT9 an average of 12.73%, and tritordeum line HT31 an average of only 6.58% averaged over the four triticales lines used as pollinators. These data show genotype effect that is highly significant (P < 0.001) both for tritordeum and triticale genotypes and highly significant (P < 0.001) female ×year, male × year and female × pollinator interactions. The behaviour of F₁ tritordeum hybrids when crossed with one of the triticale pollinators supports the conclusion that the parents' crossability behaviour is genetically controlled. Analysis of segregation ratio of F₂ hybrids plants from high and low crossability tritordeum genotypes crossed with the same triticale pollinator genotype is consistent with 9:3:3:1 ratio. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ovule and embryo culture to obtain hybrids from interspecific incompatible pollinations in chickpea

Many of the wild species of chickpea were not accessible to the improvement of chickpea due to cross incompatibility. In these interspecific incompatible crosses, fertilization takes place but the embryo aborts a few days later. The only way to obtain hybrid plants is by the application of growth regulators to pollinated pistils to prevent initial pod abscission and to save the aborting hybrid embryos by embryo rescue techniques. Although there are a few papers on regeneration from different explants of chickpea, information on embryo rescue techniques is not available. The paper summarises the embryo rescue techniques developed for chickpea, by the use of which hybrid plants between C. arietinum and C. pinnatifidum were produced. The paper also emphasises the effect of genotype to successfully obtain hybrids. The morphology of the hybrid plants resembled the male parent in leaf structure and growth habit. The colour of the flowers produced on the hybrid plant was pale violet, resembling the male parent whose flowers were violet in colour. The flower colour of the female parent was white. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crossability between cultivated and wild tuber-and non-tuber-bearing Solanums

The cultivated potato has over 200 extant wild relatives many of which contain genes valuable for disease resistance, hardiness, processing and agronomic traits. Crossability of these wild species directly with the cultivated potato is complicated by several reproductive phenomena such as stylar and ploidy barriers and Endosperm Balance Numbers (EBN). However, a systematic analysis of crossability with many of these wild relatives has never fully been examined. Reciprocal crosses were made between cultivated potato and over 400 wild potato accessions; stylar barriers and 2n gamete production were examined as was the fertility of many of the putative hybrids. Generally, the seed/fruit ratio increased the more closely related the species were to the cultivated potato. However, a few crosses were successful in spite of predicted failure due to ploidy or EBN differences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Abnormalities of endosperm development inLilium hybrids

Summary Of 191 interspecific crosses attempted between 27 different species representing different subgenera ofLilium only 14 gave rise to seeds and only 6 of these were viable. Sterility was associated with various types of abnormality in endosperm development. Many of these irregularities involved chromosome breakage and reunion but others entailed abnormal DNA replication and chromosome coiling. In one cross the individual endosperm nuclei contained four stranded structures, the behaviour of which at division was similar to that of bivalents at meiosis. The embryo-sac ofLilium is of theFritillaria type, containing both haploid and triploid polar nuclei. As a consequence the balance between the number of chromosome sets in the embryo, endosperm and maternal tissue is 2:5:2 and not 2:3:2 as is more commonly found in diploid species. It is suggested that sterility results from genetic imbalance of the endosperm itself rather than interaction of the endosperm with either embryo or maternal tissue.     

Parental effects on crossability,embryo differentiation and plantlet recovery in wheat x rye hybrids

Summary One hexaploid wheat cultivar (Triticum aestivem) and two tetraploid wheat lines (T. durum) were crossed with seventeen inbred lines of rye (Secale cereale). Seed set, degree of hybrid embryo differentiation at the time of excision for in vitro culture and recovery of amphihaploid plantlets from various embryo categories were studied. Degree of embryo differentiation was predominantly determined by maternal wheats, paternal rye genotypes appearing to be of minor importance. T. aestivum x rye hybrid embryos were superior to those produced from T. durum for degree of differentiation. The proportion of plantlets developing from differentiated embryos was high for all wheat parents, whereas undifferentiated embryos were mostly unsuitable for plantlet production. The results revealed that cross-incompatibility in hexaploid wheat x rye crosses was due to failure of fertilization, while in tetraploid wheat x rye crosses it was caused by lack of embryo differentiation. Correlation analyses showed that seed set provided a criterion to predict the amphihaploid plantlets to be expected from a particular wheat x rye combination.     

Creation of novel interspecific-interploid Hylocereus hybrids (Cactaceae) via embryo rescue

In this study we developed a technique for rescuing embryos at a very early developmental stage following interspecific-interploid crosses between Hylocereus sp. Controlled hand pollinations were performed between the tetraploid H. megalanthus (Vaup.) Bauer as the female parent and either diploid H. monacanthus (Lem.) Britton et Rose or H. undatus (Haw.) Britton et Rose as the male parent. The fertilized ovules were excised from ovaries 10 or 30 days after pollination (DAP). Pollinated ovules containing the funiculi and placental tissue and immature embryos were placed on half-strength basal Murashige and Skoog (MS) medium containing 680 μM glutamine, 0.54 μM α-naphthaleneacetic acid, and 0.45 μM thidiazuron and supplemented with 0.00, 0.09, 0.17 or 0.26 M sucrose concentrations. The best ovule response was recorded at 30 DAP, and the most prolific callus formation was observed at 10 DAP. Callus formation was observed in most of the treatments using whole ovules but not in the isolated immature embryos. The calli were mucilaginous or compact, transparent and friable, but they did not form embryogenic structures. Embryo development was significantly affected by the sucrose concentration, and the best results were obtained with 0.17 M sucrose. More than 70 % of the obtained hybrids were successfully hardened off and transplanted in soil where they grew normally. Ploidy level analyses of 77 putative hybrids exposed diploid, triploid, tetraploid, and higher than tetraploid levels. Among those hybrids studied, 22 progenies were randomly chosen for amplified fragment length polymorphism analysis, and all were identified as genuine hybrids. The technology described here is an additional stage in the breeding program for Hylocereus species resulting in novel, interspecific hybrids obtained using the embryo rescue technique.     

Production of interspecific hybrids between Glycine max and G. tomentella through embryo culture

Summary Interspecific hybrids have been obtained in an incompatible cross between Glycine max and G. tomentella through the in vitro culture of hybrid embryos. The percentage of successful pod setting in the crosses averaged 12.8% but there were marked differences depending on the soybean cultivar used as the female parent. Hybrid embryos at globular to heart stages were extracted from the embryo sac 15–25 days after pollination and cultured in vitro. Hybrid plants were successfully obtained by culturing the embryos on B5 medium supplemented with 0.1 mg/l IBA followed by culture on B5 medium supplemented with 0.1 mg/l TBA plus 0.25 mg/l 2-iP. The F1 plants resembled the wild male parent in growth form, but had an intermediate leaf shape between that of the parents.     

Fertilisation assessment and postzygotic development in several intra- and interspecific Prunus hybrids

Summary the clearing technique was applied to assess fertilisation and to follow the postzygotic development in ten intra- and interspecific crosses among Prunus species used as rootstocks. The technique allowed to distinguish fertilised ovules from unfertilised ones, as well as to calculate the fertilisation percentage in intra-and interspecific compatible crosses. All the stages from unfertilised to fertilised ovules were analysed in order to determine the best time for embryo rescue. Differences in postzygotic development among the crosses are discussed in terms of the genotype of the seed parent in the pollen-pistil interactions.Abbreviations DAP Days After Pollination     

Intersubgeneric Crossability in the Genus Glycine Willd.

In intersubgeneric crosses between wild perennial Glycine species of submenus Glycine and soybeans, Glycine max (L.) Merr., of subgenus Soja, all the putative hybrid pods aborted from 9 to 30 days after pollination (DAP). Spraying of 70 ppm gibberellic acid on hybridized gynoecia facilitated pod retention. Fluorescence microscopy revealed normal pollen germination and pollen tube growth in all the intersubgeneric crosses except in the G. cyrtoloba × G. max cross.     

Crossability,fertility and cytogenetic studies in Solanum acaule × Solanum bulbocastanum

From 538 cross combinations made between 20 accessions of S. acaule and 28 clones of S. bulbocastanum 150 different F₁'s were obtained. Average berry set was 11%, average number of seeds per berry 0.7. The accessions of both parent species could be divided into distinct groups on the basis of the crossability. Of the 72 F₁-clones examined 59 were triploid and 13 were tetraploid. Evidence is presented that the 4x-F₁'s originated from unreduced gametes produced by two bulbocastanum accessions. Pollen stainability of the 6x-, 8x-, 4x- and 3x-F₁'s was 85, 29, 12 and <5% respectively. The genomic constitutions of the F₁'s adequately accounted for these fertility relations. Selfing of F₁'s was successful with 6x-F₁'s only. Crosses between the F₁'s and S. tuberosum, tuberosum-haploids and S. demissum did not succeed in spite of the large number of pollinations made. A breeding programme is recommended to be carried out within the hexaploid hybrid populations which aims at late blight resistance and crossability with S. tuberosum. The quadruple cross (acl × blb) × (acl × tbr) and the direct cross between S. tuberosum and S. bulbocastanum are discussed.     

Production of intergeneric hybrids between Brassica and Sinapis species by means of embryo rescue techniques

Reciprocal crosses were made to produce intergeneric hybrids among seven species of Brassica and three species of Sinapis with the aid of embryo rescue techniques. Ovule culture showed better responses in terms of hybrid plant development. Altogether, hybrids from 8 different combinations were obtained from the crosses between B. campestris var. trilocularis × S. turgida, B. campestris var. pekinensis × S. arvensis, S. arvensis × B. campestris var. pekinensis, B. oleracea var. alboglabra × S. alba, B. oleracea var. alboglabra × S. turgida, B. carinata × S. alba, B. carinata × S. arvensis, and B. carinata × S. turgida. Reciprocal crosses yielded no hybrid except in the combination of S. arvensis × B. campestris var. pekinensis. Among them hybrids from 6 combinations were established in the glass house. The hybridity of the plants was confirmed by morphological characters, pollen stainability, chromosome number and by isozyme analysis. Hybrids of four combinations out of six turned out as true hybrids, one as sesquidiploids and the another one as false hybrid plant. This revised version was published online in August 2006 with corrections to the Cover Date.     

杀配子染色体在小麦-黑麦异代换系中的作用研究

利用小麦-黑麦异代换系H-13(1R/1D), H-24(5R/5A),H-33(6R/6A)与中国春-杀配子染色体二体异附加系CS-DA2C(来自山羊草Ae. cylindrica),CS-DA3C(来自山羊草Ae. triuncialis)配置杂交组合,对杀配子染色体的作用进行了研究。结果表明,杀配子染色体3C对H-13和H-24都是致死的,即有着完全的杀配子作用,但对H-33的杀配子作用则是不完全的,有着接近正常的结实率,说明不同的小麦-黑麦异代换系遗传背景对杀配子作用有很大影响,可能在品系H-33中存在对2C染色体杀配子作用的抑制基因。在以品系H-33为母本时,2个杀配子附加系F1的自交结实率差异显著,说明在相同的小麦-黑麦异代换系遗传背景下,染色体2C与3C的杀配子作用是不同的,在这2个杀配子染色体上可能带有不同的杀配子基因?这些研究结果为进一步创制小麦-黑麦易位系奠定了基础。     

Development and characterization of interspecific hybrids of Trifolium alexandrinum×T. apertum using embryo rescue

This is the first report on the development of interspecific hybrids between Trifolium alexandrinum and T. apertum using embryo rescue and characterization of F₁ plants. T. apertum was used as the male parent and T. alexandrinum as the female parent. Development of interspecific hybrids under natural conditions is not successful and so embryo rescue was attempted. Of the several combinations tried, pollination 2 days after emasculation and embryos rescued 11 days after pollination was found to be the best. For embryo culture, EC3 medium consisting of MS basal supplemented with 2.3 μM kinetin and 3% sucrose was used. Germinated embryos were transferred to LSP3 medium 25 days after inoculation wherein most of the cultures showed multiple shoots that were split and subcultured on RL1 medium for rooting. After hardening, about 75% of hybrids were successfully transferred to the field. The hybrids, in general, showed morphological traits intermediate between the two parents; however, a few hybrids showed better growth than either parent. Some F₁ plants were almost 3 weeks later in flowering than the female parent. Pollen fertility among these plants ranged from 78 to approximately 100%. Chromosomal associations at diakinesis and isozyme banding patterns for acid phosphatase (ACP), superoxide dismutase (SOD) and peroxidase also confirmed the hybrid nature of the plants.     

Crossability of tetraploid and hexaploid wheats with ryes for primary triticale production

Summary Crossability of wheat and rye was investigated during thirteen crop cycles in two contrasting locations to 1) evaluate tetraploid and hexaploid wheat parents in crosses with rye, 2) identify genotypes with high crossability and 3) assess the impact of environment on seed development. The majority of the tetraploid wheats crossed with rye had seed set around 20%, but very low embryo viability. Several wheat genotypes with seed set above 50% were identified. The hexaploid wheats crossed with rye showed poor seed set, but plant recovery was relatively high. The majority of the hexaploid wheats with highest seed set (20–30%) were from China. The results suggest differences in crossability between the rye populations, and wheat species by rye interactions. The crossability of the tetraploid and hexaploid wheats was affected by climate in the two locations.     

Diversity of abnormal embryo sacs in indica/japonica hybrids in rice demonstrated by confocal microscopy of ovaries

Embryo sac abortion occurs frequently in the spikelet of indica/japonica hybrids in rice. To provide a comprehensive understanding of embryo sac sterility in typical indica/japonica hybrids, a simple eosin B staining procedure for use with confocal microscopy was developed to observe the mature embryo sacs of 35 indica/japonica F₁s making up an incomplete diallel cross design (5 × 7). A diversity of abnormal embryo sacs existed in the hybrids. The main types were classified into five categories: (i) embryo sac degeneration (ESD), (ii) embryo sac without egg apparatus, (iii) embryo sac without female germ unit, (iv) embryo sac with abnormal polar nuclei and (v) abnormal small embryo sac (ASES). The frequencies of abnormal embryo sacs in the 35 hybrids ranged from 26.0% to 76.3%, with an average of 48.6%. The highest frequency of abnormality was 31.3% ESD. The frequencies of various abnormalities varied with parental genotype and environment.     

Interspecific compatibility barriers,development of interspecific hybrids through embryo rescue and lineage of Trifolium alexandrinum (Egyptian clover)—important tropical forage legume

Genetic improvement of Trifolium alexandrinum L. is hampered because of narrow genetic base and lack of interspecies compatibility information. The study was envisaged to understand the interspecies incompatibility and the affinity between T. alexandrinum and 22 species of the genus representing different sections and to develop interspecific crosses. Development of interspecific hybrids with T. resupinatum, T. lappaceum, T. subterraneum, T. vesiculosum and T. echinatum, through embryo rescue, revealed their affinity with T. alexandrinum. Failure of pollen germination or restricted pollen tube growth showed its distant relatedness with T. clypeatum, T. balansae, T. purpureum, T. leucanthum, T. hirtum, T. pilulare and T. hybridum. Pollen tubes reached up to ovule among the crosses with T. alpestre, T. repens and T. nigrescens, whereas it travelled up to ovary among the crosses with T. angustifolium, T. grandiflorum and T. dasyurum indicating need of manipulation to overcome barrier. Thus, incompatibility of T. alexandrinum with many Trifolium species could be overcome through embryo rescue with intensive crossing. Egyptian clover ecotype ‘Fahli’ was more compatible with other species than ‘Mescavi’.     

Crossability and cytological studies in Solanum macrocarpon and Solanum linnaeanum (Solanaceae).

Summary Crossing experiments involving the various groups of Solanum macrocarpon L. complex, including wild (dasyphyllum), semi-wild and cultivars produced fully fertile F1 and F2 hybrids. This confirmed earlier findings that these groups belong to the same biological species. S. macrocarpon complex and S. linnaeanum Hepper ex Jaeger are isolated by reproductive barriers. F1 and F2 hybrids between various groups of S. macrocarpon showed heterosis. F2 superior hybrids were isolated as candidates for the future breeding programmes. Most wild-type traits like prickliness, hairiness were dominant to those possessed by cultivars. Relatively resistant hybrids to pest attack were noted. S. macrocarpon complex and S. linnaeanum are diploids (2n=24). The overall nature of the karyotype suggests that the two are related. The F1 hybrids between the cultivars of S. macrocarpon and the wild group (S. dasyphyllum) showed normal meiosis. A lack of isolating barriers confirmed that S. macrocarpon complex constitute a single biological species.