The quantitative relationship between telomeric heterochromatin and secalin synthesis in Secale cereale L.

Summary The relationship between the amount of prolamine (secalin) synthesized and the amount of telomeric heterochromatin in ten inbred lines of rye (Secale cereale L.) cv. Self Fertile Spring was investigated. There was no association between the total amount of secalin synthesized and the amount of telomeric heterochromatin per haploid genome. However, a positive relationship was found between total secalin synthesis and the amount of telomeric heterochromatin on the short arm of chromosome 7 (7RS). Lines synthesizing high levels of secalin were found to have approximately 60% less telomeric heterochromatin on chromosome arm 7RS than lines synthesizing low levels of secalin. There was no positive relationship between secalin synthesis and the amount of telomeric heterochromatin present on any other telomere.     

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.     

Allocation of a powdery mildew resistance locus to the chromosome arm 6RL of <Emphasis Type="Italic">Secale cereale</Emphasis> L. cv. ‘Jingzhouheimai’

Chinese cultivar Jingzhouheimai of Secale cereale L. confers resistance to several important wheat diseases, making it a useful resource for wheat improvement. Octoploid amphiploid (2n = 8x = 56; AABBDDRR) was synthesized by hybridization of Jingzhouheimai with hexaploid wheat landrace Huixianhong and doubling of the F1 chromosome number. This amphiploid was backcrossed to the wheat parent to produce wheat-rye chromosome addition lines. The existing six disomic addition lines (all except 6R) were screened with 16 rye-specific DNA markers and three putative markers for 6R were identified. These markers were used in selection of chromosome 6R addition lines, confirmed by the genomic in situ hybridization (GISH). In this manner, seven monosomic 6R and five disomic addition were selected, as well as one mono-telosomic 6RS addition, one mono-telosomic and one ditelosomic 6RL additions. In turn these 6R addition lines were used to develop additional 15 6R-specific markers of which six were allocated to the arm 6RS and nine to 6RL. Screening for the powdery mildew resistance identified chromosome arm 6RL as the carrier of the resistance locus. Therefore, DNA markers identified as specific to the 6RL arm can be used to monitor the introgression of the resistance locus into wheat.     

Evidence for Monotelodisomics in Rye (Secale cereale L.)

Monotelodisomics of chromosome arms 2RL and 6RL were observed in progenies of rye trisomics. The monotelodisomic of chromosome arm 6RL (2n = 13 + 6RL) is vital and is well transmitted through the pollen. In the progeny of monotelodisomic 2RL. (2n = 13 + 2RL) no monotelodisomic but one monotelotrisomic of chromosome arm 2RS (2n = 14 + 2RS), one trisomic with an aberrant chromosome consisting (if chromosome arm IRS and a part of chromosome arm 2RL (2n = 14 + 2RSL) and one double telotrisomic of chromosome 2R (2n = 13 + 2RS + 2RL) have been identified.     

Early Embryo-Sac Development and Intraspecific Variation in the Mean Endosperm Cell Cycle Time in Vicia narbonensis (L.)

The early endosperm development in seven Vicia narbonensis populations was studied under a 23/ 16 ° C day/night temperature regime. Double fertilization occurred in less than 24 h after pollination. Endosperm divisions were synchronous until the 8th division of the endosperm nuclei. Aberrant endosperm nuclei were first observed alter the 8th division and their number increased after the 10th division. Endosperm nuclei continued to divide until the 12th day after pollination. During the following days a decrease in the number of endosperm nuclei was observed together with a substantial increase in the number of aberrants. Endosperm nuclei finally disintegrated. Neither cellularization nor starch deposition was observed in the endosperm. A positive correlation (r 0.69) was recorded between early pod length and the number of endosperm nuclei found in the ovules within each pod. In the populations studied the number of endosperm nuclei increased at a steady but different rate. This was followed by embryo development as well. It was concluded that intraspecific variation in the mean endosperm cell cycle time exists in Vicia narbonensis and that populations A 174 and A 202 should be more compatible to Vicia faba ev. ‘Polycarpe’ than population A 201.     

An embryological study of a Pisum sativum x Vicia faba cross

Summary Flowers of Pisum sativum plants grown in the field and greenhouse were self-pollinated and pollinated with Vicia faba. Germination of pollen and pollen tube growth were slower in the Pisum x Vicia cross. About 2% fertile ovules in the field and 8% in the greenhouse were obtained from the Pisum x Vicia cross, compared to 26% and 48% for Pisum x Pisum. Development of the Pisum x Vicia embryo was normal in form, though much slower than the Pisum x Pisum embryo, and about the sixth day it began to collapse. The greatest difference between the two types of crosses was observed in the endosperm. While the Pisum x Pisum endosperm nuclei divided normally and endosperm developed throughout the ovule cavity and around the embryo, the Pisum x Vicia endosperm nuclei formed only scattered masses of densely stained nuclei which were not always in close proximity to the hybrid embryo. It was concluded that faillure of some ovules to develop following Pisum sativum x Vicia faba cross pollination was the result of slow germination of pollen and slow growth of the Vicia pollen tubes, with subsequent lack of fertilization. Collapse of fertilized ovules was associated with abnormal and limited development of the hybrid endosperm, possibly leading to lack of nourishment and eventual collapse of the hybrid embryo.     

Interspecific hybridization between Vicia faba (L.) and Vicia narbonensis (L.): Early pod growth and embryo-sac development

Summary Fertilized embryo-sac development and pod growth was studied in one Vicia faba cultivar, one Vicia narbonensis population and their reciprocal crosses. The initial development of endosperm and embryo was at least four days faster in V. narbonensis than in V. faba. Pods and ovules developed also faster in V. narbonensis than in V. faba. The growth rate of the hybrid pods followed the growth rate of the mother species, but was slower than that of the pods from selfed flowers. In the cross V. narbonensis × V. faba the ovules stopped growing 9 days after pollination, while in the reciprocal cross they stopped growing 15 days after pollination. Hybrid embryo-sacs from V. faba × V. narbonensis were aborted before they reached the stage of 256 endosperm nuclei or 200 embryo cells. Selfed V. faba embryo-sacs reached this stage in less than 9 days after pollination. In the reciprocal cross the embryo-sacs were aborted before they reached the stage of 128 endosperm nuclei or 80 embryo cells. Selfed V. narbonensis embryo-sacs reached this stage at the 4th day after pollination. Given that at these stages the embryo has less than 200 cells it was concluded that an in-ovule embryo culture technique should be developed to obtain hybrid plants.     

Influence of selected wheat and rye genotypes on the direct synthesis of hexaploid triticale

Summary In the synthesis of primary hexaploid triticale, a cross-incompatibility barrier exists when tetraploid wheat (4X) is crossed with diploid (2X) rye. Fertilization may occur, however, abnormal endosperm development usually leads to premature embryo death. Four selected tetraploid wheat lines were crossed as females with seven open-pollinated rye lines and the resulting embryos were rescued in vitro 13–16 days after pollination. The wheat genotypes showed a major influence on crossability (seed set), embryo development and plant recovery. The highest efficiency of amphihaploid plant recovery (18.3 plants per 100 pollinated florets) was obtained from one 4X wheat line originally selected from the cross T. carthlicum × T. dicoccoides. Some of the 3X amphihaploid plants (ABR) derived from two wheat lines showed relatively high level of partial fertility presumably as a result of meiotic restitution. Correlation analysis showed that crossability (seed set), normal hybrid embryo development in vivo and embryo culturability were independent of each other.     

水稻胚胎和胚乳双缺陷突变体eed1的表型与遗传分析

从由化学诱变剂甲基磺酸乙酯(ethylmethane sulfonate,EMS)处理的粳稻品种中花11突变体库中,筛选到一个可稳定遗传的胚胎和胚乳发育缺陷的突变体,命名为embryo and endosperm defective 1 (eed1)。eed1籽粒千粒重、颖果的粒长、粒宽、粒厚、萌发率、总淀粉、直链淀粉和贮藏蛋白系列指标较野生型均显著降低。eed1颖果严重皱缩,且胚乳呈粉质。利用扫描电镜观察发现,与中花11相比, eed1胚乳中淀粉粒排列疏松,多以单一、分散的淀粉粒存在,且呈近似球形。eed1胚胎结构异常,部分颖果未见有胚胎分化的痕迹。qRT-PCR发现, eed1胚乳中参与淀粉和贮藏蛋白合成的大部分基因表达下调。利用eed1与籼稻南京6号杂交得到的F2分离群体进行基因定位分析,将EED1定位于9号染色体长臂672kb的范围内,包含114个开放读码框。本研究为进一步解析EED1基因调控水稻胚胎和胚乳发育的机制奠定了基础。     

Grain development and endoreduplication in maize and the impact of heat stress

The post-anthesis development of growing maize kernels is strongly affected by heat stress. The maize cultivar “Spezi” was used to quantify this effect in kernels from 14 days after flowering until maturity. Day/night temperature of control plants was 25/20°C. Stress of 40/25°C was given for seven days or continuously up to maturity. Kernels were analysed weekly for dry matter and extractable DNA. In addition the ploidy levels and the DNA content in intact cell nuclei were determined by flow cytometry. The dry matter reduction started immediately after heat treatment and reached, at maturity, 40% for temporary heat stress and 60% for permanent heat stress. The reduction of extractable DNA started later and was not as extensive. Endopolyploidy was found in all kernel tissues, namely embryo, endosperm and pericarp. In endosperm, 3C nuclei reached their maximum number at approximately 14–17 days, and cells with higher ploidy levels between 21 and 26 days after flowering. Later on 6C nuclei were dominant. The DNA content in intact cells of the endosperm reached a maximum 21 days after flowering. This maximum was lower for heat stress variants and decreased more rapidly. Heat stress can vary from year to year under field conditions. Since heat stress changes the ratio between embryo and endosperm DNA in the direction of a higher portion of embryo DNA at maturity, this has an influence on the measured content of GM DNA from GM pollen transfer into conventional maize fields.     

玉米籽粒突变体smk7的表型分析和基因定位

利用甲基磺酸乙酯(EMS)对玉米自交系B73进行诱变,获得一个可以稳定遗传的小籽粒突变体smk7(small kernel 7)。smk7成熟籽粒表现为体积变小,胚和胚乳发育缺陷,百粒重显著降低。突变籽粒发芽率仅为10%,且幼苗黄化不能生长成正常植株。成熟smk7胚乳中淀粉、蛋白、油分含量与野生型籽粒相比无显著差异,但突变体胚乳淀粉粒体积明显变小且形状不规则。smk7突变籽粒在授粉后12 d即可观察到明显的小籽粒和空瘪表型,石蜡切片显微观察显示突变籽粒的胚和胚乳发育迟缓,胚乳基部转移层细胞(BETL)相对于野生型细胞壁向内生长减少,发育受阻。用杂合植株(+/smk7)与多个自交系分别杂交,构建不同背景的F2分离群体,遗传分析结果表明该性状受单隐性核基因控制。利用靶向测序基因型分型(genotyping by target sequencing,GBTS)技术将基因初定位于2号染色体短臂,进一步精细定位发现该基因位于RM1433917和RM1535316两个标记之间约120 kb的物理范围内,共有8个蛋白编码基因。本研究为进一步克隆和解析SMK7基因调控玉米籽粒发育的分子机制奠定了基础。     

小麦-黑麦代换系间、代换系与易位系间杂交后代染色体易位系的选育

为了选育有经济价值的易位系,探讨小麦-黑麦间产生易位的频率,本研究以小麦-黑麦代换系DS5R/5A和DS6R/6A为母本,以小麦-黑麦易位系克珍(Kezhen)和带有杀配子染色体的代换系DSGC1为父本,分别进行田间杂交。结果表明:DS5R/5A、DS6R/6A与DSGC1(2S)杂交结实率低,平均为27.7%,与克珍(T3B.3R)杂交结实率高于前者,平均结实率为59.3%,二者均好于远缘杂交的结实率,这也表明带有杀配子染色体的亲本影响结实率;对选出的54株DS5R/5A×DSGC1、DS6R/6A×DSGC1杂种后代与80株DS5R/5A×克珍、DS6R/6A×克珍杂种后代进行C-分带、原位杂交和分子标记鉴定后发现,二者的易位频率分别为11.1%和8.8%,并且多为染色体端部小片段易位,这种小片段易位可能是代换系间杂交部分同源染色体交换产生的。此外,也表明杀配子染色体在引起染色体断裂后可发生染色体易位。本研究共获得T5RL.5AS、T5RS.5DL、T5RS.5BL、T6RL.6DS、6RL.6BS以及T6RS.6BL等13个易位系,平均易位频率为9.6%。     

玉米籽粒突变体smk7的表型分析和基因定位

In this study, a stable small kernel mutant, named small kernel 7 (smk7), was isolated from ethylmethane sulfonate (EMS) mutagenesis of maize inbred line B73. Compared with wild type, the smk7 mutants showed smaller kernel size, defective embryo and endosperm development and a significant decrease in 100-kernel weight. The smk7 kernels showed a low level of germination rate at 10% and cannot grow into normal plants. No significant changes were detected in protein, starch and oil content between mature wild type and smk7 kernels, but the starch grains became significantly smaller and irregular in smk7 kernels compared with wild type. The smk7 kernels could be clearly distinguished from the wild type as early as 12 days after pollination (DAP), on the basis of their smaller and emptier phenotype. Microscopic inspection of the paraffin sections revealed that the development of embryo and endosperm were delayed, and the cell wall in growth in basal endosperm transfer layers (BETL) were arrested in smk7 compared with wild type. The F₂ populations with multiple backgrounds were constructed by crossing heterozygous plants (+/smk7) with several other inbred lines. Genetic analysis showed that the mutant phenotype was controlled by a single recessive gene. Based on genotyping by target sequencing (GBTS) strategy, the SMK7 was initially mapped on the short arm of chromosome 2. The fine mapping results suggested that SMK7 was located between markers RM1433917 and RM1535316, with a physical distance of 120 kb. There were eight protein-coding genes in this region. This study laid a foundation for further genes cloning and research of the SMK7 function in regulating maize kernel development.     

Crosses between Hordeum vulgare L. and H. bulbosum L. II. Elimination of chromosomes in hybrid tissues

Summary In interspecific crosses between diploid and autotetraploid cytotypes of Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass), several kinds of hybrid endosperm, vegetative tissue and generative tissue were studied. In all these tissues, mitotic disturbances occurred which resulted in chromosome elimination. The chromosomes of H. bulbosum were eliminated more frequently than those of H. vulgare.Differences between the three types of tissue might have been due to differences between their mitotic rhythms. Differences between various kinds of the same type of tissue were discussed in relation to the ratio of the total number of genomes in embryo, endosperm and maternal tissue, and the ratio of the genomes of the parental species within the hybrid nuclei. For both ratios assumptions as to the genetic value of each genome were taken into account.The cause of the disturbances was probably genic disharmony between the parental genomes.     

Molecular identification of Pm12-carrying introgression lines in wheat using genomic and EST-SSR markers

The traditional process of obtaining maize hybrids involves the generation of inbred lines through successive generations of selfing and subsequent testcrosses in order to identify the best combining ability by allelic complementation. A fast alternative to obtain inbred lines is to induce the formation of haploids followed by chromosome doubling. However, even with the aid of haploid-inducing genetic sources, this strategy has not been widely used in maize breeding programs, partly due to difficulties inherent to haploid generation and identification. In order to evaluate the possibility of using dihaploids to generate homozygous maize tropical lines, we used the androgenetic haploid inducer line W23 as a female parent in crosses with the tropical single-cross hybrid BRS1010. Within the progeny of these crosses, 462 seeds were phenotypically selected as putative haploids by the purple-colored endosperm and colorless embryo conditioned by the R1-nj gene. Among these, only four individuals were confirmed as being haploids using SSR markers, chromosome counting and flow cytometry, showing that the phenotypic marker was not efficient in detecting haploids in the tropical maize genotype used. All four haploids as well as some diploid plants presented reduced size, corroborating the difficulties for haploid identification by phenotypic evaluation. Genetic diversity analysis revealed by SSR markers divided the haploids in two groups represented by flint and dent maize inbred lines, which could be helpful in identifying complementary dihaploid lines. The present article demonstrates that a combination of haploid production and SSR fingerprinting is a feasible strategy for maize hybrid development in tropical germplasm.     

Embryo lethality in wheat × rye hybrids—mode of inheritance and the identification of a complementary gene in wheat

Crosses between hexaploid wheat and rye can only succeed when pre- and post-zygotic barriers have been overcome. A rye gene determining embryo lethality (Eml-R1), which is involved in post-zygotic isolation, has been mapped to chromosome 6R. In the present paper the mode of inheritance of Eml-R1 was studied by employing a wheat/rye chromosome 6R addition line. We show that Eml-R1 exists in at least two alternative forms, with the mutant allele Eml-R1b being dominant with respect to wild-type Eml-R1a. Furthermore, we have exploited nulli-tetrasomic lines of wheat to detect a complementary wheat gene present on chromosome 6A. This gene has been designated Eml-A1.     

Intraspecific Variation in Mean Endosperm Cell Cycle Time in Vicia faba (L.) and Interspecific Hybridization with Vicia narbonensis (L.)

The rate of early embryo-sac development was studied in seven faba bean (Vicia faba L.) cultivars grown in a controlled environment. The embryo-sac stage was determined from the number of endosperm nuclei per embryo-sac and the number of embryo cells during the first 12 days after pollination. Differences in early embryo-sac development were observed between the genotypes studied. In addition, five different V. faba×V. narbonensis crosses and reciprocals were made using genotypes with small differences in mean endosperm cell cycle time and genotypes with large differences. The percentage of success (pod set) in V. faba×V. narbonensis crosses ranged between 9 % and 59 % while in the reciprocals it ranged from 12 % up to 30 %. However, cytological studies showed that the high percentage of success (pod set) observed in the cross A-107 × A-202 was not associated with a higher percentage of interspecific hybrid embryos. The results indicate that genotypes of the two species with smaller differences in mean endosperm cell cycle time result neither in a higher percentage pod set nor in bigger hybrid embryos.     

Isolation of mildew resistant wheat-rye translocation lines from a double substitution line

A powdery mildew resistant double disomic wheat-rye substitution line carrying rye chromosomes 1R and 2R was crossed with normal bread wheats. The F₂ generation was analysed cytologically by C-banding. Wheat-rye chromosome translocations involving both rye chromosomes 1R and 2R were frequent in F₂. Lines with translocations of 1R and 2R were harvested separately. After four generations of selfing and selection for mildew resistance and fertility, fully fertile resistant lines were selected and analysed cytologically. Lines with 1BL/1RS and 2BS/2RL translocations were identified. The resistance on chromosome 1RS could not be shown to be different from control varieties carrying the same rye segment, while the resistance on 2RL is much broader than the earlier known 2RL derived resistance in the line Transec. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of Rye Chromosome 1R Translocations and Substitutions in Hexaploid Wheats Using Storage Proteins as Genetic Markers

Grain protein compositions of 106 advanced generation backcross lines from crosses involving ‘Amigo’ (1AL.1RS), ‘Aurora’, ‘Kavkaz’, ‘Skorospelka-35’ and ‘Sunbird’ (all 1BL.1RS) and ‘Gabo’ 1DL.1RS parents and 152 cultivars with unknown pedigree were analysed by one-dimensional SDS-PAGE. Eighty seven backcross lines and 16 cultivars carried one or other of these translocations, 2 cultivars had a 1R (1B) substitution, whereas 5 backcross lines were found to be heterogeneous for the 1BL.1RS translocation. The translocation lines were easily identified by the presence of secalins (Sec-1) controlled by rye chromosome arm IRS and a simultaneous loss of the gliadin (Gli-1) and/or triticin (Tri-1) protein bands controlled by the replaced wheat chromosome arm (1AS, 1BS or 1DS). Certain gliadins, showing no allelic variation among the genotypes analysed, were identified as markers for chromosome arms 1AS (M_r= 34 kd) and IBS (M_r= 42,33 kd). The whole chromosome substitutions 1R (1B) were recognized by scoring for the presence of Sec-1 and HMW secalin bands, Sec-3 (controlled by rye chromosome arm 1RL) and the absence of Gli-B1 and HMW glutenin subunits, Glu-B1 (controlled by wheat chromosome arm 1BL). The results have shown that protein electrophoresis provides a rapid and reliable technique for screening genotypes for these translocations and substitutions in a breeding programme.     

Problems in breeding and cytology of sugar cane

In connection with the increase of chromosome number found in species hybrids of Saccharum the author studied embryo-sac development within several Saccharum froms from early stages of meiosis in the embryo-sac mother cells to stages where fertilization already had taken place.Normally by meiosis within E M C's a row of four haploid megaspores is formed from which the innermost, the chalazal megaspore, develops into an embryo-sac and the other three degenerate.Haploid embryo-sacs, thus formed, may occur in Saccharum. Frequently however, in Saccharum endo-duplication takes place, that is splitting of the chromosomes within the nucleus of the chalazal megaspore, through which the chromosome number is increased.It is described how within Saccharum by this phenomenon embryo-sacs may be formed with diploid and tetraploid chromosome numbers and with numbers between haploid and diploid.The increase of chromosome number, observed in the young megaspore after meiosis, could be confirmed by counting the chromosomes of dividing nuclei within young embryo-sacs.Chromosome numbers found in dividing zygotes and endosperm nuclei within fertilised embryo-sacs also pointed to the occurrence of egg-cells and polar nuclei that must be haploid, diploid and tetraploid.The significance of this research in relation to plant breeding will be discussed in Part V.