Genome size variation among sex types in dioecious and trioecious Caricaceae species

Caricaceae is a small family consisting of 35 species of varying sexual systems and includes economically important fruit crop, Carica papaya, and other species of “highland papayas”. Flow cytometry was used to obtain genome sizes for 11 species in three genera of Caricaceae to determine if genome size differences can be detected between sexes. Genome sizes ranged from 442.5 to 625.9 megabases (Mb) likely due to variation in the accumulation of retrotransposons in the genomes. The C. papaya genome size was estimated to be 442.5 Mb, larger than previously reported. Significant differences were detected between male and female samples in Jacaratia spinosa, Vasconcellea horovitziana, and V. stipulata, and between male and hermaphrodite samples of V. cundinamarcensis, suggesting the presence of sex chromosomes for these species. The small size differences between genomes of the papaya sexes were not detected using flow cytometry. Vasconcellea horovitziana was discovered to have a larger female genome size than male, suggesting the possibility of a ZW sex chromosome system in the family. The estimated genome sizes of these 11 species will be used in sequencing their genomes and in sex chromosome research for this family.     

甘蔗近缘属植物氮磷钾养分效率的变异分析

为了筛选养分高效甘蔗种质资源及培育养分高效甘蔗品种,采用系统聚类分析法,分别以地上部干重,植株N、P、K素吸收效率和利用效率为指标,将40份具有代表性的甘蔗近缘属植物进行了分类。结果表明,甘蔗近缘属植物地上部干重变幅为1.26~39.6 kg/穴,变异系数为75.92%。云南82-85地上部干重是象草82-21的40.78%,但云南82-85的N、P、K素利用效率分别是象草82-21的4.9、1.7和3.2倍。不同类型甘蔗近缘属植物的地上部干重,N、P、K素营养效率的极差很大,可分为若干组,各组间差异显著,且同组内材料的N、P、K素营养效率之间也存在显著性差异。上述研究结果对选育营养高效的新型种质和阐明营养高效的生理机制具有一定参考价值。     

基于甘蔗热带种(LA-purple)全基因组序列的SSR开发及特征分析

现代甘蔗栽培品种(2n = 100~130)是由甘蔗热带种(2n = 80)与割手密(2n = 40~128)种间杂交而来, 形成异源多倍体、非整倍体作物, 使得甘蔗栽培品种中80%~90%的染色体来源于热带种。开发热带种基因组SSR分子标记, 有助于甘蔗遗传多样性分析、分子标记辅助选择、遗传图谱的构建等。本研究基于热带种LA-purple的全基因组测序数据的255 398个预测基因序列(累计总长为1 029 222 285 bp), 利用Perl程序与生物信息学软件结合, 发掘SSR位点, 获得了153 150个SSR位点, 平均每1.67个基因有1个SSR位点, 其中二、三核苷酸重复基序分别为39 556个和50 072个, 占总SSR位点数的58.5%。在二核苷酸重复基序中, TA/AT所占比例最高, 占41.4%, CG/GC所占比例最低, 占4.6%; 在三核苷酸碱基重复基序中, TGT/ACA所占比例最高, 为15.6%。在TA/AT重复类型中选取100个基序重复次数在60~90之间的SSR位点, 进行引物设计与合成, 在12个甘蔗属材料中进行PCR扩增分析, 从中筛选出52对具有多态性SSR引物, 其中有27对引物在研究的2个甘蔗栽培品种间表现为多态。这些基因组SSR标记的开发, 不仅可以用于甘蔗栽培品种DNA指纹图谱分析, 而且为甘蔗属不同种的遗传图谱构建、遗传多样性分析和重要性状的遗传机制解析奠定基础, 为甘蔗分子育种研究提供重要支撑。     

Glandular hair densities in three perennial Medicago species

Summary Eight triazine resistant (Brassica napus x B. oleracea) x B. oleracea interspecific hybrids with chromosome numbers ranging from 25 to 27 were backcrossed a second time to B. oleracea but no seed was formed. However, in vitro embryo rescue on 77 developing ovules yielded nine BC₂ plants with chromosome numbers between 19 and 25 and in which the herbicide resistance was still strongly expressed. Three of these plants (NOH-8B2B1, 2n=20; NOH-8B2B3 and NOH-8B2B4, 2n=19) were backcrossed again to B. oleracea. Two of the three plants produced seed which germinated to produce triazine resistan BBC₃s with 18, 19 or 20 chromosomes. The triazine resistant B. campestris cytoplasm has now been stabilized in B. oleracea.     

Genome size and Giemsa C-banded karyotype of tetraploid Bromus ciliatus L.

Summary Tetraploid Bromus ciliatus L. is a North American bromegrass that has been placed in the Pnigma section of Bromus. The objective of this study was to characterize the genome of tetraploid B. ciliatus by cytogenetic methods and compare it to the genomes of other species included in the section Pnigma. All the plants of the accession (USDA PI 232214) selected for chromosome counting were tetraploids (2n = 28). The mean 2C nuclear DNA content for tetraploid B. ciliatus was 19.13± 0.07 pg as determined by flow cytometry which is significantly greater than the tetraploid DNA content of B. inermis Leyss. (11.74± 0.16 pg). C-banding procedures were used to identify individual mitotic chromosomes and to develop a karyotype for B. ciliatus. The genome of the tetraploid B. ciliatus consisted of 16 median chromosomes, eight submedian chromosomes, and four chromosomes with satellites which included one pair with a large satellite and one pair with a small satellite. The general pattern of the distribution of constitutive heterochromatin in B. ciliatus was quite different than the other bromegrasses that have been analyzed to date. Except for two pairs of chromosomes, all chromosomes in tetraploid B. ciliatus had telomeric bands on one or both arms. Some of the chromosomes with telomeric bands had centromeric bands that were located at one or both sides of the centromere and intercalary bands which were generally absent in the other bromegrass species. It was possible to identify all chromosomes of tetraploid B. ciliatus and to match the pairs of homologous chromosomes by using chromosome lengths, arm length ratios and C-banding patterns. The results of this study indicate that tetraploid B. ciliatus has different genomes than the European species evaluated to date in the section Pnigma.     

Somaclonal variation in explant-derived potato clones over three tuber generations

Summary Tuber characteristics of potato clones (Solanum tuberosum L.) regenerated from cultured leaf, rachis or stem pieces of cv. Desiree were assessed in field trails over three years. In the first two seasons, when the crop was grown for seed potato production, tuber numbers and the tuber yields were normally distributed and the population means of the clones were about the same as those of the controls. When 78 of the clones were grown as a ware crop in a replicated field trial there were statistically significant differences between most clones and the controls in total yield (generally lower) and ware yield (generally higher), brought about by alterations of the size distributions of tubers. In all years the population of clones had fewer scab (Streptomyces scabies) lesions than the controls. Clones with consistent differences in flesh colour and eye depth were also observed. Two out of 78 clones, in 1984, had significantly higher dry matter content. No stable decrease in susceptibility to the cyst nematode Globodera pallida was observed amongst 167 clones tested. These potato plants regenerated from explants clearly show that somaclonal variation can include agronomically relevant changes.     

Genetic variation in leaf epidermal cell size and shape in Lolium perenne

Summary Six diploid perennial ryegrass populations, two diploid F₁ hybrid families and the autotetraploid cv. Tove were grown in a glasshouse and the mean length and mean width of epidermal cells on the abaxial leaf surface of young fully expanded leaves compared. The diploids varied in cell length by 26%, in cell width by 9% and in length: width ratio by 39%. The cells of cv. Tove were 25% longer and 12% wider than those of the highest ranking diploid and the length: width ratio 9% higher. The DNA contents per telophase root-tip cell nucleus of a large-celled and a small-celled diploid population were similar, suggesting that the variation in epidermal cell size among diploids was due to the action of specific genes and not to differences in genome size. The mean epidermal cell dimensions of four of the above populations growing as plots in a field trial employing three levels of fertiliser nitrogen and four harvesting frequencies were measured on three occasions. Varietal ranking in cell dimensions was consistent over the different managements and dates, and agreed well with the glasshouse results. The results indicate that measurements of leaf epidermal cell length and width can be useful aids both in breeding for herbage yield and in distinguishing varieties with similar flowering dates.     

The variation rules of pupil size under classroom lighting condition

For the purpose of studying the rule of the pupil size variation while the luminance level is changing under the classroom’s lighting condition, the variation values of 3 student’s pupil area that under 5 kinds background luminance affording by three kinds of fluorescent illuminant of different color temperature (2 700 K, 4 000 K, 6 500 K)are measured, with iView X eye tracking and the experiment of the measure system of pupil size under classroom lighting to simulate the classroom lighting.The result shows that, the relationship between pupil area and background luminance is negative exponential function under 3 color temperature fluorescent illuminant;under the classroom lighting condition, the pupil area gets smaller when the background luminance is higher, and is getting stable gradually;under the same background luminance, the pupil area is smaller under the lighting of higher color temperature fluorescent.     

Exploring the natural variation for reproductive thermotolerance in wild tomato species

Climate change has become a serious threat for crop productivity worldwide. The increased frequency of heat waves strongly affects reproductive success and thus yield for many crop species, implying that breeding for thermotolerant cultivars is critical for food security. Insight into the genetic architecture of reproductive heat tolerance contributes to our fundamental understanding of the stress sensitivity of this process and at the same time may have applied value. In the case of tomato (Solanum lycopersicum), germplasm screenings for thermotolerance have often used yield as the main measured trait. However, due to the complex nature of yield and the relatively narrow genetic variation present in the cultivated germplasm screened, there has been limited progress in understanding the genetic basis of reproductive heat tolerance. Extending the screening to wild accessions of related species that cover a range of climatic conditions might be an effective approach to find novel, more tolerant genetic resources. The purpose of this study was to provide insight into the sensitivity of individual reproductive key traits (i.e. the number of pollen per flower, pollen viability and style protrusion) to heat-wave like long-term mild heat (LTMH), and determine the extent to which genetic variation exists for these traits among wild tomato species. We found that these traits were highly variable among the screened accessions. Although no overall thermotolerant species were identified, several S. pimpinellifolium individuals outperformed the best performing cultivar in terms of pollen viability under LTMH. Furthermore, we reveal that there has been local adaptation of reproductive heat tolerance, as accessions from lower elevations and higher annual temperature are more likely to show high pollen viability under LTMH.     

Colchicine-induced variation of cell size and chloroplast number in leaf mesophyll of rice

Comparisons were made in the C₁ generation between the untreated controls (2x) and colchicine‐treated diploids (C2x) for variation of leaf mesophyll cell size and chloroplast number. Differences were found in that the cell section area and the number of chloroplasts per cell in all the seven lines investigated were significantly greater in the C2x selections compared with the 2x controls using coded determination. In each case, there was an enhancement of chloroplast number independent of the variation in cell size.     

Structure of variation among morphological and physiological traits in three pearl millet composites

Summary The plant breeder's task of improving and stabilizing many plant traits simultaneously is complicated by interrelationships that occur among the traits. Factor analyses were conducted on three phenotypically diverse pearl millet [Pennisetum glaucum (L.) R. Br.] composites to describe the structure of relationships among yield, morphological, and physiological traits. Approximately 1000 S₀ spaced-plants from each composite were evaluated for 20 traits, and random samples of 289 S₁ progenies from each composite were evaluated for 18 of these traits. Factors extracted in S₀ and S₁ populations identified unique sets of traits that were interrelated along axes of (a) biological yield, (b) panicle size, (c) dry matter partitioning and (d) compensation between number and size of seeds. Several plant traits had large loading coefficients on the Biological Yield and also, but with opposite signs, on the Dry Matter Partitioning factor. The traits having large loading on these two factors differed between space-planted and normal-density stands, showing that environmental conditions contributed to the associations observed among traits. Correlations of S₁ with parental S₀ factor scores for the Biological Yield, Panicle Size and Seed Paramters factors produced significant correlation coefficients, indicating that these trait complexes had a genetic basis. The implications of these results for millet breeding are discussed.     

Towards flexible management of postharvest variation in fruit firmness of three apple cultivars

Stochastic modeling provides a useful tool in managing biological variation in the postharvest chain. In the current study, the fruit-to-fruit variability in the postharvest firmness of apples was modeled. Apples from three cultivars (‘Jonagold’, ‘Braeburn’, and ‘Kanzi’) were harvested at different levels of maturity, and stored at different temperatures and controlled atmosphere (CA) conditions. By using a kinetic model describing firmness breakdown as a function of time, temperature, controlled atmosphere conditions and endogenous ethylene concentration, the main stochastic variables were identified as the initial firmness and the rate constants for firmness breakdown and ethylene production. Treating these variables as random model parameters, the Monte Carlo method was used to simulate the propagation of the fruit-to-fruit variability in flesh firmness within a batch of apples during storage under different CA conditions and subsequent shelf-life exposure. The model was validated using independent data sets from apples picked in a different season. The model developed in this study can be used to predict the probability of having apples of certain firmness after long term storage for different scenarios of temperatures and CA conditions.     

甘蔗和斑茅Ⅲ型过氧化物酶基因（SoPOD-1和SaPOD-1）cDNA克隆与分析

研究旨在通过克隆甘蔗和斑茅Ⅲ型过氧化物酶基因(Prxs),分析比较2个物种Prxs基因差异,探讨2个物种Prxs功能差异的遗传基础。采用同源克隆方法,以高粱Prxs基因序列为探针,克隆获得甘蔗和斑茅Prxs基因。本研究从斑茅和甘蔗中成功克隆获得了4个Prxs基因cDNA序列,其中斑茅2个基因长度均为1083 bp,存在一个差异位点,甘蔗2个基因长度均为1084 bp,存在11个碱基差异。4个基因开放阅读框均为996 bp,编码331个氨基酸。蛋白质保守结构域分析表明,克隆获得的4个基因均具有Prxs典型保守结构域,为目标基因。系统进化分析表明,克隆获得的基因与高粱、玉米和水稻的同源基因相似性最高,在一些双子叶植物,甚至裸子植物也能找到其同源基因,且氨基酸序列的相似程度与物种分化的程度基本一致,可供植物分类作参考。该试验从斑茅和甘蔗中成功克隆获得了4个Prxs基因cDNA序列,为深入研究Prxs基因在不同植物中功能差异提供了一定的参考。     

Somaclonal variation in three Argentinean varieties of Triticum aestivum with different karyotypic instability*

Three cultivars of wheat showing different levels of spontaneous karyotypic instability were studied regarding their stability in vitro for a number of characters, i.e. chromosome structure, gliadin pattern, glume and grain colour, awn type, chlorophyll pigmentation and plant morphology. The progenies of somaclones derived from immature embryos of both aneuploid and euploid plants were used in this study along with foundation seeds and a large number of their sexual progeny in order to discriminate between pre-existent variability and any novel variation induced by the in vitro culture. Only one translocation not described before and a new gliadin pattern were detected which could be ascribed to the effects of tissue culture, suggesting that this technique is not effective for inducing novel variation for breeding purposes in wheat.     

Karyotype analysis and interspecific hybridisation in three perennial Sesbania species (Leguminosae)

Summary The somatic chromosome number in Sesbania sesban var. nubica, S. goetzei and S. keniensis (Leguminosae; Papilionoidae) was found to be 2n=12. These findings were in agreement with earlier reports on S. sesban and S. keniensis. The chromosome number 2n=12 is a new record for S. goetzei. Similarities in karyotypes were found in the three species. All species had one pair of long metacentric chromosomes; the second pair was submedian, followed by four smaller pairs of metacentric chromosomes. Nucleolar organiser regions in the form of satellites were found on the short arm of the fourth chromosome pair in S. sesban and S. keniensis. Interspecific crosses in all possible combinations were carried out, resulting in pod and viable seed formation for the crosses S. sesban x S. goetzei, S. sesban x S. keniensis, S. goetzei x S. sesban and S. goetzei x S. keniensis. The two crosses with S. keniensis as a female parent were unsuccessful. The hybrid plants established normally and produced viable seeds.     

Sample size required for marker assisted selection in improving quantitative traits of self-fertilizing species

The efficiency of selection for desired trait genotypes in a molecular marker assisted selection for a quantitative trait in self-fertilizing crop is considered. The QTLs controlling the trait were assumed to be unlinked. It was supposed that the selection starts in F₂, derived from a cross between inbred lines, and this selection will terminate if one or more plants with the desired trait genotype is found. If no plant with the desired trait genotype is found in F₂ then the selection is continued in the F₃ progeny that is derived from a single selected F₂ plant. Which F₂ plant is to be selected was determined according to the rank which is related to the marker genotype of the F₂ plants. And this rank was based on the expected frequency of the desired trait genotype in the progeny. The plant with the top rank among all F₂ plants is then selected with the first priority. Additionally the number of F₃ plants in the progeny was set to be equal to the number of plants that are required for detecting one or more plants with the desired trait genotype with a given probability. The probability of getting at least one plant with the desired trait genotype is expressed as a function of the number of F₂ plants (N).The required value for N and the total number of plants (T) in F₂ and F₃ for detecting at least one plant with the desired trait genotype were calculated for different situations. T was always smaller for a single marker than for flanking markers. The minimum of T and monotonous decrease of N can be observed when the cumulative-expected-frequency of selected marker genotypes of F₂ plants increased. This revised version was published online in July 2006 with corrections to the Cover Date.