Analysis of nucleolar organizer regions by silver staining in two Lolium species

Summary The nucleolar organizer activity of diploid and tetraploid Lolium perenne L. and diploid Lolium multiflorum Lam. varieties was analyzed by the silver staining procedure. Both species show six or twelve Ag-NORs (silver stained nucleolar organizer regions) at the diploid and tetraploid levels, respectively. A positive correlation between the size of secondary constrictions and Ag-NORs was observed.     

Resistance to rice sheath blight (<Emphasis Type="Italic">Rhizoctonia solani</Emphasis> Kühn) [(teleomorph: <Emphasis Type="Italic">Thanatephorus cucumeris</Emphasis> (A.B. Frank) Donk.] disease: current status and perspectives

Sheath blight (ShB) disease, caused by Rhizoctonia solani, is an economically important rice disease worldwide, especially in intensive production systems. Several studies have been conducted to identify sources for ShB resistance in different species of rice, including local accessions and landraces. To date, none of the genotypes screened are immune to ShB, although variation in levels of resistance have been reported. Several quantitative trait loci (QTL) for ShB resistance have been identified using mapping populations derived from indica or japonica rice. A total of 33 QTL associated with ShB resistance located on all 12 rice chromosomes have been reported, with ten of these co-localizing with QTL for morphological attributes, especially plant height, or for heading date. Sixteen QTL, from the same or differing genetic backgrounds, have been mapped at least twice. Of these, nine QTL were independent of morphological traits and heading date. We hypothesize that two main, distinct, mechanisms contribute to ShB resistance: physiological resistance and disease escape. Strategies to improve our understanding of the genetics of resistance to ShB are discussed.     

Genotyping by sequencing of 270 Indica rice varieties revealed genetic markers probably related to heavy metal accumulation

Genotyping by sequencing (GBS) has been applied to identify genetic markers in crops for trait association and breeding purposes. Here, we applied GBS technology to study a natural population of 270 Indica rice strains, which resulted in identification of 79,545 genomewide single nucleotide polymorphisms. Using these SNPs, we found the close relationship between the 270 Indica rice strains. Furthermore, we tested the feasibility of using these 270 Indica strains in studying important rice traits by analysing the cadmium and other metal accumulation of these strains and correlating the traits with genetic markers. We identified 32 SNPs to be associated with cadmium (Cd) accumulation, explaining 61.25% of the Cd concentration variances in grains. The genetic markers provided here are valuable resources for future rice studies, and further characterization of the candidate loci identified in this study can also aid the development of low Cd‐accumulating rice varieties.     

New C-banding pattern for chromosome identification in cucumber (Cucumis sativus L.)

A chromosome study of cucumber, C. sativus L., was performed using orcein and C-banding techniques. The diploid and tetraploid plants investigated here showed the somatic chromosome numbers 2n=14 and 28, respectively. The haploid chromosome complement was composed of five metacentric and two submetacentric chromosomes. All C. sativus chromosomes had clearly visible C-bands, and each chromosome could be identified unequivocally after C-banding staining, with 13 C-bands appearing in the haploid complement. The haploid complement had a 44.9% ratio of total C-band length to total chromosome length. Chromosomes 1, 2, 4, 5 and 7 had stable C-bands. Three large, dark C-bands appeared at the proximal regions of chromosomes 1 and 2. Chromosome I had quite a large C-band and with a 68.4% ratio of C-band length to short arm length. Chromosome 2 also had quite a large C-band in the pericentromeric region with a 57.6% ratio of C-band length to the full length of this chromosome and possessed an elongated primary constriction in early metaphase. In prometaphase, chromosome 2 showed that the long arm was completely separated from the short arm. The number of secondary constrictions could not be clearly observed because these chromosomes are small and they could not be counted in every metaphase cell. However, six chromosomes seemed to have secondary constrictions in the diploid plants. Two silver-stained bands were observed at primary constrictions of two of the large chromosomes.     

Genetic variation in bean bacterial pathogens

Summary In this review, genetic variation has been reported in bacterial pathogens of Phaseolus vulgaris L., Xanthomonas phaseoli, Pseudomonas phaseolicola, corynebacterium flaccumfaciens, and Pseudomonas syringae based on degrees of virulence and cultural characteristics. P. phaseolicola, which was reported as consisting of 2 races, was found to comprise numerous strains. A correlation between appearance on special culture medium and virulence was reported for strains of X. phaseoli. Occurrence of the bacterial pathogens complicates control through breeding and maintaining resistant cultivars.Research reported was conducted under Project 21-016, Nebraska Agricultural Experiment Station, Lincoln.     

江汉平原大豆品系表型分析及综合评价

种质资源是大豆育种的基础,理论方法是品种选育的关键。以64份大豆品系为材料,采用变异性分析、相关性分析、因子分析和聚类分析等多元分析方法相结合,对大豆品系的10个农艺性状及产量性状进行研究,筛选适宜江汉平原种植的大豆品系,同时探究影响大豆产量的关键因素,为选育优质高产大豆品种提供种质和理论依据。结果表明,大豆品系10个农艺性状的变异系数为4.19%~46.95%,有效分枝数变异系数最大,蛋白质含量变异系数最小;因子分析将10个农艺性状转化为4个主因子,分别为产量构成因子、株高因子、粒重因子和品质因子,累计贡献率为80.067%。由农艺性状与综合得分相关性分析可知,生育期、株高、主茎节数、单株荚数、单株粒数、单株粒重和蛋白质含量7个农艺性状可作为大豆品系综合评价指标。聚类分析将64份大豆品系分成3个类群,类群Ⅰ31份,类群Ⅱ24份,类群Ⅲ 9份,类群Ⅲ大豆品系综合表现较好,适宜在江汉平原种植。     

Marker-assisted identification of resistance genes to soybean mosaic virus in soybean lines

Soybean plants react differentially to soybean mosaic virus (SMV) strains because of interactions among different resistant genes in the soybean genome. Three independent genes resistant to SMV have been identified by inheritance studies and linkage analyses. To develop durable SMV-resistant soybean cultivars, it is necessary to determine which soybean SMV resistance genes can be readily transferred from resistant to susceptible cultivars in a breeding system. Here, we report the type and number of resistance gene(s) in four Korean elite soybean cultivars using a combination of disease reaction symptoms, inheritance studies, and molecular marker mappings. The disease reactions of Sowonkong and Keunolkong soybean varietals in response to infection with SMV strains suggested that both cultivars most likely harbor the Rsv1 gene similar to that in York. Subsequent inheritance studies confirmed that Sowonkong has the Rsv1 gene. The inheritance studies suggested that Sinpaldalkong harbored the Rsv1 gene, which was then confirmed by molecular marker mapping. The inheritance studies also suggested that Jinpumkong 2, which is the most resistant to SMV infection among the four cultivars, contained the Rsv1 and Rsv3 genes; this was confirmed by molecular marker mapping. Our approach, which combined inheritance studies and molecular linkage analyses, allowed the efficient identification of resistance gene(s) in four Korean soybean cultivars.     

Cytogenetic Studies of Hybrids between Festuca gigantea Vill. and Lolium multiflorum Lam.

The meiotic behaviour of the hybrid between Festuca gigantea (2n – 6x = 42) and Festuca gigantea (2n = 6x = 42) indicates distinct structural differences between the two species. These differences are also apparent in the degree of chromosome pairing observed in Lolium multiflorum×F. gigantea compared with previous reports on the L. multiflorum×F. arundinacea hybrids. Although the L. multiflorum×F. gigantea 8x amphiploid com Dines the complementary characters of the two species and is agronomically interesting, there are some irregularities in meiotic behaviour that could affect the stability of the amphiploid. Seed fertility in the amphiploid is high and preliminary studies show evidence of a high degree of self-fertility. The pentaploid hybrid between autotetraploid L. multiflorum×F. gigantea is sufficiently fertile to be used as the pollen plant in crosses with diploid L. multiflorum (BC₁). Backcrossing the BC₃ hybrid to L. multiflorum results in mainly diploid progeny. The possibilities, of using this crossing scheme to introgress F. gigantea characters into L. multiflorum is discussed as an alternative approach to amphiploid breeding as a means o: combining specific complementary characters of the two species.     

Genetic variation between Spanish and American versions of sweet corn inbred lines

Conservation of maize inbred lines in different stations causes variability among strains. The objective of this research was to determine agronomic and molecular differences in American sweet corn inbreds maintained in Spain. American and Spanish strains of five sweet corn inbred lines were characterized by using 34 RAPD primers that produced 168 consistent bands. Strains of four of these inbreds were crossed in a diallel design, and hybrids were evaluated in four environments in northwestern Spain. The RAPD characterization showed no differences between strains for two inbreds, while divergence between strains was largest for the inbred 15125. Most primers did not reveal any variability between pairs of strains, while some primers produced variations at high rates. Differences in agronomic performance among Spanish and American strains were most important for P51, followed by P39, while strains 1453 or 15125 were not significantly different. Molecular differences between strains were not related to agronomic performance. Residual heterozygosity or outcrossing cannot explain these results. Lack of adaptation could have caused stress‐induced mutagenesis. Natural selection could have eliminated unfavourable selective mutations, but neutral mutations can be found at the molecular level and favourable mutations could have been selected at the agronomic level.     

Differential preference of <Emphasis Type="Italic">Capsicum</Emphasis> spp. cultivars by <Emphasis Type="Italic">Aphis gossypii</Emphasis> is conferred by variation in volatile semiochemistry

The aim of this study was to demonstrate that Capsicum spp. cultivars are differentially preferred by the cotton aphid, Aphis gossypii, and to investigate the role of volatile semiochemicals in conferring differences in host preferences. Two preference assays were conducted in 2008 under greenhouse conditions. Fourteen different commercially available cultivars were grown in cages protected by an anti-aphid net, and were infested 60 days after planting, through the release of ten adult female A. gossypii per plant. The results showed that after a five-day infestation period, statistically significant differences in the mean number of A. gossypii between cultivars were observed, with Sweet Pepper Hybrid Green Belt (SPHGB) being one of the cultivars with the lowest number of A. gossypii per plant. To test the hypothesis that the preference of cultivars was associated with release of volatile, Capsicum spp-derived semiochemicals, olfactometer behavior bioassays were conducted with A. gossypii, using volatile organic compounds (VOCs) collected from non-preferred SPHGB and preferred SPAB cultivars. A. gossypii was significantly repelled only by the VOCs of infested SPHGB. Furthermore, coupled gas chromatography-mass spectrometry (GC-MS) analysis of VOCs released by plants prior to, and after, A. gossypii infestation, revealed that the non-preferred SPHGB cultivar released nine additional compounds after infestation, including 6-methyl-5-hepten-2-one, a known plant defense semiochemical involved in plant—aphid interactions. These data suggest that non-preferred cultivars releasing this semiochemical have the potential to be used in breeding programs aimed at producing A. gossypii-resistant Capsicum spp. cultivars.     

陆地棉配合力与杂种优势、遗传距离的相关性分析

 用10个陆地棉亲本进行不完全双列杂交,共配置了45个组合,计算亲本的一般配合力（GCA）、特殊配合力(SCA)、杂种优势,并结合SSR标记研究了陆地棉亲本配合力与杂种优势、遗传距离之间的相关关系。配合力分析发现,10个亲本的一般配合力和特殊配合力存在显著或极显著差异。分析亲本配合力、杂种优势和遗传距离的相关性发现,子棉产量、皮棉产量、衣分的一般配合力和杂种优势呈显著或极显著相关,纤维长度、比强度、麦克隆值、株高、果枝数、单株铃数、铃重、子棉产量、皮棉产量、衣分的特殊配合力和杂种优势均呈极显著正相关,而与遗传距离相关均不显著。单株铃数、铃重、子棉产量、皮棉产量、衣分的杂种优势与遗传距离均为正向显著或极显著相关。在育种实践中这些显著或极显著相关的性状可能具有较高的改良潜力。     

Revised calculation of the coefficient of parentage in plant breeding

The knowledge of the genetic similarity between two individuals has been useful for animal breeders for a long time, and one of the most common measures of similarity is the Coefficient of Parentage (COP). For two individuals X and Y, it is defined as the probability that an allele taken from a particular locus in individual X is equal by descent to another allele taken from the same locus in individual Y; thus, the COP between two individuals is the same as the expected inbreeding of their offspring, and it is now a routine calculation among plant breeders as part of crop improvement programmes. Nevertheless, plant breeders deal with the genealogy between strains or groups of individuals, and here, we provide a mathematical proof that in this case the application of standard formulae replicated from animal breeding may result in overestimation of the true amount of inbreeding between two strains.     

The genetic basis for low coefficient of infection to stem rust in common wheat

Summary Resistance to several Australian strains of Puccinia graminis f. sp. tritici in four entries of the 1963 International Spring Wheat Rust Nursery, viz 25 (W3300), 318 (W3301), 386 (W3302) and 409 (W3303), was shown to have in each case a complex basis. In W3300 seedling resistance was controlled by Sr5, Sr9b, and a third, dominant gene, designated SrN, which conditioned resistance to all Australian strains. W3301 possessed the recessive gene sr17, and a new gene, srK1, which was effective against 16 of the 18 strains used. A third gene, SrK2, operated in adult plants only.W3302 was shown to carry Sr11, and two genes, SrM1 and srM2, both apparently derived from Marquillo. Five already known genes, viz Sr5, Sr6 Sr8, Sr9b and sr17, and an undescribed dominant gene SrR were isolated from W3303. SrR appeared to be allelic with SrN.The present studies suggest that worldwide resistance shown by the four entries was due in each instance to a combined effect of genes already catalogued by Sr numbers and new genes. In each entry the new genes, either singly or in combination, provided resistance to Australian strains which have genes for virulence on the designated genes.     

Genetic analysis of in vitro plant tissue culture responses and regeneration capacities

Summary The in vitro development of a whole plant from a single cell (eg microspore or somatic cells) is a characteristic feature of plants. The amenability of a plant to in vitro culture is influenced by the genotype, which is thus of major importance in the plant tissue culture response. The differences observed between different cultivars during in vitro tissue culture with respect to embryogenesis and regeneration result from quantitative or qualitative genetic differences. We describe results obtained from quantitative genetic studies, from Mendelian genetic analysis and from gene mapping. It is less easy to study the influence of cytoplasmic genomes. Moreover, it is necessary to discriminate between maternal effects and cytoplasmic inheritance. A conclusion from this review is that the choice of parental strains for a breeding program should be realized on agronomic criteria rather than on compatibility with the tissue culture technique used. Fortunately, it is relatively easy to incorporate short-term tissue culture capacity into agronomically valuable genotypes. This is of major interest since tissue culture remains necessary for most aspects of crop plants biotechnology. Very little is known about the molecular events that trigger in vitro embryogenesis and regeneration. It is clear that genes involved in the tissue culture response are not specialised tissue culture genes.     

Large yield differences between reciprocal families of Solanum tuberosum

Summary A number of reports have indicated differences in reciprocal families of Solanum tuberosum when intergroup hybrids were studied. Questions have been raised concerning the potential magnitude, frequency, and genetic basis for such differences. In this study, exact reciprocal crosses were made using parents characterized by different maturities and having different cytoplasmic sources within Solanum tuberosum in order to substantiate previous claims of reciprocal differences and to clarify the nature of such differences.Field trials revealed reciprocal differences which were large and highly significant. Reciprocal yield differences of up to 115% were observed when parents of opposite maturities were used. In seven crosses, the higher-yielding reciprocal always had the higher-yielding parent as the maternal parent. Significant reciprocal differences for flowering and vine maturity were also observed between some families. The F₂ populations were generated for one set of reciprocals and the reciprocal differences in the F₂ generation seemed to be substantially reduced relative to the F₁ generation.It is concluded that the occurrence of large reciprocal differences seems to depend more upon having parents of opposite maturity than upon the taxonomic origin of the parent's cytoplasm. This, in conjunction with the reduced F₂ reciprocal differences, suggests that observed differences may be due to very persistent maternal effects or a type of dauermodification, rather than true cytoplasmic inheritance.Cooperative Investigation of U.S. Department of Agriculture, Science and Education Administration. Agricultural Research and the Wisconsin Agricultural Experiment Station.     

Genes for resistance in barley to Finnish isolates of Rhynchosporium secalis

Summary Twenty Finnish isolates of Rhynchosporium secalis (Oud.) J.J. Davis, the causal agent of scald, were taken from infected barley (Hordeum vulgare L.) plants and inoculated on to seedlings of a differential series of barley containing a range of major genes for resistance to the fungus, as well as on to six Nordic 6-row spring barleys and three winter ryes (Secale cereale L.). These fungal isolates derived from four sites and three host varieties. Disease development was monitored on two leaves of seedlings in the greenhouse employing a standard scale, and on adult plants in the field by assessing the diseased area on the three uppermost leaves. A comparison was also made between the pathogenicity and virulence of ten Finnish and ten Canadian R. secalis isolates. The Finnish isolates varied in virulence, but with the exception of Algerian (CI 1179) seedlings and adult La Mesita (CI 7565) all seedlings and adult plants of the entire differential series were resistant to all isolates. Canadian isolates were, on average, less virulent than Finnish isolates. All the Nordic checks were susceptible to all Finnish and seven Canadian isolates, but differences in the degree of susceptibility were evident. Isolates of R. secalis from barley were non-pathogenic on rye, isolates from Elymus repens L. were non-pathogenic on barley and rye, and isolates from rye were only pathogenic on rye. Finnish R. secalis isolates contain no redundant pathogenic diversity. The differential series represents a useful, but as yet untapped, source of resistance to R. secalis for Finnish barley breeders.     

Methods for Plant Differential Expressed Gene Cloning and Progress

The research of plant genome has been transferred from the structural genomics focusing on determining the complete sequences of the genome to the functional genomics focusing on elucidating the biological function of genes. Now cloning differential expressed genes is of prime interest in molecular biology. In the past ten years, some methods used for studying changes of gene expression in plants have been developed. The authors review the developments of techniques and studies for the plants related gene cloning in RNA level and expound their principles, technical routes, improved methods, advantages and defects. Moreover, their applications and prospects in plants related studies are discussed.     

Genetic characteristics of Korean weedy rice (Oryza sativa L.) by RFLP analysis

Summary The genetic characteristics and classification of 24 strains of Korean weedy rice, two strains of foreign red rice, three Japonica cultivars, one Tongil cultivar and one Indica cultivar (Oryza sativa L.) were investigated at the DNA level using the restriction fragment length polymorphism (RFLP) method. Eighty-three random combinations between six restriction enzymes and forty genomic DNA probes (RG# and KR#) were assayed. Thirty-seven (92.5%) out of the forty probes used showed polymorphisms among the 31 accessions assayed. A high level of polymorphism was found between short and long grain type Korean weedy rices, whereas fewer polymorphisms were presented among strains within each grain type. A dendrogram summarizing genetic similarity coefficients among thirty-one accessions was constructed based on their DNA polymorphisms. The Korean weedy rice strains were classified into two groups identical to the short and long grain types classified by morphological and physiological characters. From the RFLP analysis, it was deduced that the short grain strains of Korean weedy rice belonged to Japonica, while the long grain strains were closer to Indica than to Japonica, and were differentiated into a local ecotype surviving in the growth conditions in the southern part of the Korean peninsula.     

Classification of some indigenous maize collections from Southern and Southeastern Europe

A race classification, based on multiple variate analysis using 23 morphological characteristics, was applied to 42 indigenous maize strains from Southeastern Europe, 20 race collections from Spain and 2 Corn Belt Dent hybrids from the United States. Based on the evidence obtained and on comparisons with other studies, the Southeastern European strains were assigned to one of seven races or race groups, of which at least five appear on historical evidence to be derived directly or by recent hybridization from importations originating in North America. In contrast, the majority of the Spanish collections appeared to have their origins in importations from Central America or the West Indies. Very little similarity was observed between the Spanish and Southeastern European collections, when considered overall.Detailed classification and study of European maize appears highly desirable as an aid to utilization of this potentially valuable germ plasm in world maize breeding programs.