Genetic analysis of bacterial blight resistance in seventy-four cultivars of rice,Oryza sativa L.

Summary The genetics of resistance to bacterial blight, Xanthomonas oryzae (Uyeda and Ishiyama) Dowson, for 74 cultivars of rice, Oryza sativa L., was studied. The PX061 isolate of bacterial blight from the Philippines was used for inoculation of parental and hybrid populations. Single dominant genes at the Xa 4 locus convey resistance in 38 cultivars. Of these, 18 are resistant at all stages of plant growth and thus have the Xa 4 ^aallele for resistance. However, 20 are susceptible up to maximum tillering stage but are resistant at booting and flowering stages. These cultivars have the Xa 4 ^ballele for resistance. Thirty-two cultivars have single recessive genes for resistance which are allelic to xa 5.The resistance in DV85, DV86 and DZ78 is conditioned by two genes. At maximum tillering stage xa 5 conveys resistance. However, at later growth stages an additional dominant gene, designated Xa 7 in DZ78, also gives resistance. The dominant genes of DV85 and DV86 are probably allelic to Xa 7. Xa 7 segregates independently of Xa 4, xa 5 and Xa 6, however like Xa 6, it conveys resistance at booting and post-booting stages only.The resistance in PI 231129 is conditioned by a single recessive gene, designated xa 8. It also segregates independently of Xa 4, xa 5 and Xa 6.     

Genetic analysis of brown planthopper resistance in twenty varieties of rice,Oryza saliva L.

Summary The inheritance of resistance to brown planthopper, Nilaparvata lugens (Stol.), of 20 rice cultivars was studied. Single dominant genes that are allelic to Bph 3 condition the resistance in cultivars Ptb 19, Gangala (Acc. 7733), Gangala (Acc. 15207), Horana Mawee, Kuruhondarwala, Mudu Kiriyal and Muthumanikam. Single recessive genes that are allelic to bph 4 govern the resistance in cultivars Gambada Samba, Heenhoranamawee, Hotel Samba, Kahata Samba, Kalukuruwee, Lekam Samba, Senawee, Sulai, Thirissa and Vellai Illankali. The resistance in Ptb 33, Sudu Hondarwala, and Sinna Sivappu is governed by one dominant and one recessive gene which segregate independently of each other. The dominant resistance genes in these cultivars appear allelic to either Bph 1 or Bph 3. Similarly, the recessive genes in these cultivars seem allelic to either bph 2 or bph 4. Further investigations are needed to conclusively determine the allelic relationships of resistance genes in Ptb 33, Sudu Hondarwala and Sinna Sivappu.     

Localization of the Laevigatum powdery mildew resistance gene to barley chromosome 2 by the use of RFLP markers

Summary The powdery mildew disease resistance gene Ml(La) was found to belong to a locus on barely chromosome 2. We suggest that this locus be designated MlLa. Linkage analysis was carried out on 72 chromosome-doubled, spring-type progeny lines from a cross between the winter var Vogelsanger Gold and the spring var Alf. A map of chromosome 2 spanning 119cM and flanked by two peroxidase gene loci was constructed. In addition to the Laevigatum resistance locus the map includes nine RFLP markers, the two peroxidase gene loci and the six-row locus in barley.     

Phleomycin resistance as a dominant selectable marker for plant cell transformation

Tobacco cells are sensitive to bleomycin and phleomycin. The Tn5 and the Streptoalloteichus hindustanus (Sh) bleomycin resistance (Ble) genes conferring resistance to these antibiotics have each been inserted into two plant expression vectors. They are flanked by the nopaline synthase (nos) or the cauliflower mosaic virus (CaMV) 35S promoters on one side, and by the nos polyadenylation signal on the other. These four chimaeric genes were introduced into the binary transformation vector pGA 492, which were thereafter mobilized into Agrobacterium tumefaciens strain LBA 4404. The resulting strains were used to transform Nicotiana tabacum cv. Xanthi nc using the leaf disc transformation procedure. In all cases, phleomycin- and bleomycin-resistant tobacco plants were regenerated from transformed cells under selective conditions; however the highest frequency of rooted plants was obtained when transformation was carried out with the Sh Ble gene under the control of the 35S promoter. Phleomycin resistance was stably transmitted to sexual offspring as a dominant nuclear trait as confirmed by Southern blotting.     

Inheritance of resistance to potyviruses in Phaseolus vulgaris L. II. Linkage relations and utility of a dominant gene for lethal systemic necrosis to soybean mosaic virus

Summary A single dominant factor, Hss, that conditions a rapid lethal necrotic response to soybean mosaic virus (SMV) has been identified in Phaseolus vulgaris L. cv. Black Turtle Soup, line BT-1. Inoculated plants carrying this factor developed pinpoint necrotic lesions on inoculated tissue followed by systemic vascular necrosis and plant death within about 7 days, regardless of ambient temperature. BT-1 also carries dominant resistance to potyviruses attributed to the tightly linked or identical factors, I, Bcm, Cam, and Hsw, so linkage with Hss was evaluated. No recombinants were identified among 381 F₃ families segregating for potyvirus susceptibility, thus if Hss is a distinct factor, it is tightly linked to I, Bcm, Cam, and Hsw. BT-1 was also crossed reciprocally with the line Great Northern 1140 (GN 1140) in which the dominant gene, Smv, for systemic resistance to SMV was first identified. Smv and Hss segregated independently and are co-dominant. The (GN 1140 x BT-1) F₁ populations showed a seasonal shift of the codominant phenotype. Evaluation of the (GN 1140 x BT-1) F₂ population under conditions where Smv is partially dominant allowed additional phenotypic classes to be distinguished. Pathotype specificity has not been demonstrated for either Smv or Hss. Genotypes that are homozygous for both dominant alleles are systemically resistant to the virus and in addition show undetectable local viral replication or and no seed transmission. This work demonstrates that a gene which conditions a systemic lethal response to a pathogen may be combined with additional gene(s) to create an improved resistant phenotype.     

Satellited chromosomes,systematics and phylogeny inTaraxacum (Asteraceae)

A survey is made of the occurrence, nature and frequency of satellited chromosomes in the agamospermous genusTaraxacum. Species belonging to the 10 sections thought to be most primitive in the genus lack satellited chromosomes. In most other sections, a characteristic satellited chromosome is seen with a large euchromatic region distal to the presumed nucleolar oraniser region (NOR). In sections of a precursor type, there is always one chromosome of this Taraxacum type per haploid genome. In sections thought to be of an advanced type the number of such satellited chromosomes is very unstable, sometimes even within the same tissue. In sectionHamata, two such satellited chromosomes are invariably found in triploids. This finding strongly supports the integrity of this section, suggests that the species of the section are monophyletic, and have evolved from a single ancestor subsequent to the occurrence of obligate agamospermy. In three sections of the genus, satellited chromosomes of the conventional type with a very small distal euchromatic region distal to the NOR are reported for the first time in the genus.     

Molecular mapping of a new gene Rrs4 CI 11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar Ingrid and the resistant accession CI 11549 (Nigrinudum) was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance CI 11549 against isolate 4004. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC₃-lines into Ingrid from CI 2222 (another Nigrinudum) resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in Nigrinudum. Various resistance donors of Ethiopian origin designated as Nigrinudum, Jet or Abyssinian were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.     

RFLP mapping of three new loci for resistance genes to powdery mildew (Erysiphe graminis f. sp. hordei) in barley

Three new major, race-specific, resistance genes to powdery mildew (Erysiphe graminis f. sp. hordei) were identified in three barley lines, RS42-6*O, RS137-28*E, and HSY-78*A, derived from crosses with wild barley (Hordeum vulgare ssp. spontaneum). The resistance gene origining from wild barley in line RS42-6*O, showed a recessive mode of inheritance, whereas the other wild barley genes were (semi)-dominant. RFLP mapping of these three genes was performed in segregating F₂ populations. The recessive gene in line RS42-6*O, was localized on barley chromosome 1S (7HS), while the (semi)-dominant genes in lines RS137-28*E, and HSY-78*A, were localized on chromosomes 1L (7HL) and 7L (5HL), respectively. Closely linked RFLP clones mapped at distances between 2.6cM and 5.3 cM. Hitherto, specific loci for powdery mildew resistance in barley had not been located on these chromosomes. Furthermore, tests for linkage to the unlocalized resistance gene Mlp revealed free segregation. Therefore, these genes represent new loci and new designations are suggested: mlt (RS42-6*O), Mlf (RS137-28*E), and Mlj (HSY-78*A). Comparisons with mapped QTLs for mildew resistance were made and are discussed in the context of homoeology among the genomes of barley (H-vulgare), wheat (Triticum aestivum), and rye (Secale cereale). Duplications of RFLP bands detected in the neighbourhood of Mlf and mlt might indicate an evolutionary interrelationship to the Mla locus for mildew resistance.     

Effect of Gamma Irradiation on Embryogenic Avocado Cultures and Somatic Embryo Development

Embryogenic avocado cultures were exposed to ionizing irradiation in order to determine its effect on proliferation and subsequent somatic embryo development. The approximate PD₅₀ as determined by linear regression is 35 Gy 2 weeks after irradiation for Fuerte 2.11.1 and 4 weeks after irradiation for T362 2.11.1. Irradiation of embryogenic cultures did not significantly affect the number of early stage Fuerte 2.11.1 somatic embryos that developed directly from irradiated cultures; however, 10–50 Gy inhibited somatic embryo development. Irradiation of T362 2.11.1 embryogenic cultures at 25–50 Gy inhibited the number of intermediate and mature stages of somatic embryos that developed directly from irradiated cultures, and 50 Gy inhibited somatic embryo maturation. Inhibition of somatic embryo development could be partially offset by proliferation of irradiated embryogenic cultures as suspensions. Irradiation up to 10 Gy significantly increased the number of mature Fuerte 2.11.1 somatic embryos that developed from suspension cultures. Irradiation with doses up to 25 Gy stimulated development of heart stage T362 2.11.1 somatic embryos; however, mature somatic embryo development was suppressed at dosages of 10 Gy and greater.     

The hemoglobins of Artemia salina. V. Genetic variation in hemoglobin 1, hemoglobin 2, and hemoglobin 3

Electrophoretic mobilities of three hemoglobins (Hb1, Hb2, and Hb3) were studied in 15 populations of brine shrimps. Genetic segregation data support the model that Hb2 contains n -polypeptides and n -polypeptides; Hb1 contains 2n -polypeptides. Hb3 contains neither - nor -polypeptides. There is no evidence of linkage of and loci with each other or with the locus (or loci) which governs Hb3 or with the nonhomologous portion of the sex chromosomes. Hemoglobins of different populations may be hybridized in vitro by incubation at high temperature. Reversible dissociation to subunits which contain only one ( or ) polypeptide occurs at 40 C (for Hb1) and at 50 C (for Hb2).Supported by Grant HD-11445 from the National Institutes of Health.     

Inheritance and linkage of isozyme loci in almond

The segregation of seven isozyme marker genes was investigated using eight controlled crosses in almond. The cultivar Nonpareil was the maternal parent in all crosses. Pollination was achieved using eight different cultivars, and a total of 3200 individual kernels were assessed. For each isozyme the goodness-of-fit test was used to test for departure from the expected frequencies assuming Mendelian inheritance. Given a higher than expected number of significant results for individual isozymes, independent segregation between pairs of isozymes was tested using the chi-square statistic on the resulting two-way contingency tables. In all crosses a highly significant association (P value< 0.001) was observed between (1) the AAT- 1 and IDH isozymes loci and (2) the LAP-1 and PGM-2 isozymes loci, which leads to the conclusion that the respective isozyme pairs are linked.In addition, a significant association (P value < 0.001) was observed between LAP-1 and GPI-2 when the pollen sources were Fritz, Mission, or Price, but this could not be tested for the remaining five pollen sources, Carmel, Grant, Keane, Ne plus Ultra, Peerless, because they are homozygous at these loci. If LAP-1 is linked with GPI-2 and PGM-2, it might be expected that we should find evidence of linkage between GPI-2 and PGM-2. The lack of a significant association between these two isozymes suggests that LAP-1 is located centrally on the chromosome. These three pairs of linked loci are the first to be reported in almond.     

Analysis of molecular markers associated with powdery mildew resistance genes in peach (Prunus persica (L.) Batsch)xPrunus davidiana hybrids

A progeny of 77 hybrids issued from a cross between two heterozygous Prunus, peach [P. persica (L.) Batsch] (variety Summergrand) and a related species, P. davidiana (clone 1908), was analysed for powdery mildew resistance in five independent experiments. This population was also analysed for its genotype with isoenzyme and RAPD markers in order to map the genes responsible for resistance. A genetic linkage map was generated for each parent. The Summergrand linkage map is composed of only four linkage groups including 15 RAPD markers and covering 83.1 centiMorgans (cM) of the peach nuclear genome, whereas the P. davidiana linkage map contains 84 RAPD markers and one isoenzyme assigned to ten linkage groups and covering 536 cM. Significant associations between molecular markers and powdery mildew resistance were found in each parent. For P. davidiana, one major QTL with a very strong effect and five other QTLs with minor effects were located in different linkage groups. For Summergrand, three QTLs for powdery mildew resistance, with minor effects, were also detected. Consequently, evidence is given here that the powdery mildew resistance of P. davidiana clone 1908 and P. persica variety Summergrand is not a monogenic character but is controlled by at least one major gene and several minor genes.     

Erratum: Cloning and sequencing of the phycocyanin gene from Spirulina maxima and its evolutionary analysis

The genes were cloned for the two apoprotein subunits, and ,of phycocyanin from the cyanobacterium Spirulina maxima = Arthrospiramaxima) strain F3. The - and -subunit gene-coding regionscontain 489 bp and 519 bp, respectively. The -subunit gene is upstreamfrom the -subunit gene, with a 111-bp segment separating them.Similarities between the -subunits of S. maxima and nine othercyanobacteria were between 58% and 99%, as were those between the -subunits. The maximum similarity between the - and -subunits from S. maxima was 27%.     

A simple method for maintaining high multiplication of Narcissus shoot cultures in vitro

A simple method for stimulating and maintaining high in vitro multiplication of Narcissus shoot clump cultures was developed. Shoot clumps were subjected either to normal cutting where leaves were trimmed to 20 mm in length at the beginning of each culture passage or to severe cutting where shoot clumps were cut down to the basal plate region removing all green tissue. Severe cutting at the beginning of each culture passage initially doubled the leaf multiplication, compared to normal cutting, but the difference between cutting treatments declined in successive passages. The improvement in leaf multiplication was maintained when shoot clumps were subjected to severe cutting only at every other culture passage, with no cutting in the alternate recovery passages. In vitro multiplication was increased by severe cutting in all seven Narcissus cultivars which were tested.Abbreviations NAA-1 naphthylacetic acid - BAP benzylaminopurine     

Both common and specific genetic factors are involved in polygenic resistance of pepper to several potyviruses

Absolute resistance to potato virus Y pathotype 0 (PVY 0), potyvirus E and chili veinal mottle virus (CVMV) and a partial resistance to potato virus Y pathotype 1,2 (PVY 1,2) were found in an Indian pepper line, Perennial. In the doubled haploid (DH) progeny from the F₁ of a cross Perennial by Yolo Wonder, resistance to CVMV was confered by two independent genes, one with a clear dominant effect. Resistance to PVY and potyvirus E was quantitatively expressed and controlled by several recessive genetic factors. Genetic analysis showed that fewer resistance factors were necessary to explain resistance to PVY (0) and potyvirus E than resistance to PVY(1,2). Genetic correlations between resistances to the different potyviruses in the DH progeny showed that most of genetic factors involved in PVY(0) resistance appear to be also involved in potyvirus E resistance, and some of these polyvalent factors may be also involved in PVY(1,2) resistance but, in this case, additional specific genes were necessary. One of the two CVMV resistance genes seems to be implicated in potyvirus E resistance. Thus, the polygenic resistance of Perennial to these potyviruses was due both to polyvalent genetic factors, i.e. factors that apparently interact with several viruses, and strain-specific genetic factors.     

Use of RFLP markers for the identification of alleles of the Pm3 locus conferring powdery mildew resistance in wheat (Triticum aestivum L.)

The objective of this study was to identify molecular markers linked to genes for resistance to powdery mildew (Pm) in wheat using a series of Chancellor near-isogenic-lines (NILs), each having one powdery mildew resistance gene. A total of 210 probes were screened for their ability to detect polymorphism between the NILs and the recurrent parent. One of these restriction fragment length polymorphism (RFLP) markers (Xwhs179) revealed polymorphism not only between the NILs for the Pm3 locus, but also among NILs possessing different alleles of the Pm3 locus. The location of the marker Xwhs179 was confirmed to be on homoeologous chromosome group 1 with the help of nullitetrasomic wheat lines. The linkage relationship between this probe and the Pm3 locus was estimated with double haploid lines derived from a cross between wheat cvs Club and Chul (Pm3b). The genetic distance was determined to be 3.3±1.9 cM.     

Cell wall teichoic acids of actinomycetes of three genera of the order actinomycetales

The structures of cell wall teichoic acids of the members of newly recognized genera of the order Actinomycetales were studied. Planotetraspora mira VKM Ac-2000^T contains two types of teichoic acids: 2,3-poly(glycerol phosphate) substituted with -D-Galp at C-1 of glycerol and 1,3-poly(glycerol phosphate) substituted with -L-Rhap at OH-2 of glycerol (60%). Herbidospora cretacea VKM Ac-1997^T contains the chains of 1,3-poly(glycerol phosphate) partially substituted with -D-Galp and -D-GalpNAc at C-2 of glycerol. The majority of -D-galactopyranosyl residues are substituted at OH-3 with a sulfate. The aforementioned teichoic acids have not been found in bacteria thus far. Actinocorallia herbida VKM Ac-1994^T contains poly(galactosylglycerol phosphate), with the -Galp-(12)-Gro-P repeating units being linked via the phosphodiester bonds between the OH-3 of glycerol and OH-6 of galactose. Earlier, this structure was found in the cell wall of Actinomadura madura. The polymer structures were determined by chemical analysis and using ¹³C-NMR spectroscopy. The results show that teichoic acids are widespread in the order Actinomycetales.     

Heritable variation in the phaseolin protein of nondomesticated common bean,Phaseolus vulgaris L.

Summary Crude protein extracts from single seeds of nondomesticated Mexican bean accessions were analysed by SDS polyacrylamide gel electrophoresis for variability in phaseolin protein. Six new phaseolin types; M1, M2, M3, M4, M5, M6, which contained polypeptides within the same range of molecular weights (51,000 to 45,000 daltons) as occur in the S, T and C phaseolin types of cultivated beans were identified. No T and C types were found among the non-domesticated Mexican accessions, and the S type occurred in less than 7% of the seeds screened. Genetic analyses of F₂ progenies from crosses between Sanilac (S), and five of the M types showed that each M phaseolin phenotype was allelic to the S type and expressed codominantly.     

Structure of the cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>6</Subscript><Emphasis Type="Italic">f</Emphasis> complex: new prosthetic groups,Q-space,and the ‘hors d’oeuvres hypothesis’ for assembly of the complex

3-Å crystal structures of the cytochrome b₆f complex have provided a structural framework for the photosynthetic electron transport chain. The structures of the 220,000 molecular weight dimeric cytochrome b₆f complex from the thermophilic cyanobacterium, Mastigocladis laminosus (Kurisu et al. 2003, Science 302: 1009–1014), and the green alga, Chlamydomonas reinhardtii (Stroebel et al. 2003, Nature 426: 413–418), are very similar. The latter is the first structure of a integral membrane photosynthetic electron transport complex from a eukaryotic source. The M. laminosus and C. reinhardtii structures have provided structural information and experimental insights to the properties and functions of three native and novel prosthetic groups, a chlorophyll a, a -carotene, and a unique heme x, one copy of which is found in each monomer of the cytochrome b₆f complex, but not the cytochrome bc₁ complex from the mitochondrial respiratory chain of animals and yeast. Several functional insights have emerged from the structures including the function of the dimer; the properties of heme x; the function of the inter-monomer quinone-exchange cavity; a quinone diffusion pathway through relatively narrow crevices or portals; a modified reaction scheme for n-side quinone redox reactions; a necessarily novel mechanism for quenching of the bound chlorophyll triplet state; a possible role for the bound chlorophyll a in activation of the LHC kinase; and a structural and assembly role for the four small PetG, L, M, and N subunits. An hors doeuvres hypothesis for assembly of the complex is proposed for the small hydrophobic stick or picket fence polypeptides at the periphery of the complex, based on the cis-positive orientation of the small hydrophobic subunits and the toothpick binding mode of the -carotene.     

The complex life-cycle of a polymorphic prokaryote epibiont of the photosynthetic bacterium Chromatium weissei

In natural populations of the anaerobic phototrophic bacterium Chromatium weissei, many cells support a prokaryotic epibiont. This epibiont appears in several forms, all from the life cycle of a single species. A typical epibiont consists of one to five flattened coccoid cells stacked one above the other, perpendicular to the C. weissei surface. The cells at the proximal and distal ends of the stack are 0.6 m in diameter and 0.8 m in length; mid-stack cells are slightly shorter. A typical three or four cell stack is 2 m in length. Small mesosome-like inclusions in the distal cell are involved in the development of droplet shaped cells which are released from the end of each stack. These specialised droplet cells probably transfer to new hosts when C. weissei cells collide, thereafter developing into new epibiont stacks. It is likely that the epibiont grows heterotrophically using the substantial production of dissolved organic carbon within the dense plates of photosynthesising C. weissei which develop naturally. Thus the epibiont uses its unusual method of growth and dispersion to maintain position in the microbial plate upon which it depends.