Sex determination in the dioecious Melandrium

Summary Melandrium album (2n=24), a dioecious species with heteromorphic sex chromosomes (XY, males and XX, females), has a strong genetic commitment for sex determination. We report here a procedure for obtaining haploid plants from cultured anthers and show that genotype, pollen stage, cold treatment and certain culture media components are essential for a reproducible yield of embryos. Our procedure increased the number of responsive anthers and not the number of responsive microspores per anther. Most likely, our experimental system allows the recovery of competent microspores, and this on a medium containing either an auxin or a cytokinin. All of the 36 anther-derived plants tested expressed a female phenotypic sex instead of the theoretical one male one female ratio. When analysed cytologically, the plants exhibited the corresponding female genetic sex (one or two X chromosomes).     

Analysis of karyotype and C-banding pattern ofNicotiana plumbaginifolia using two techniques

The morphological study of the chromosomes ofNicotiana plumbaginifolia was carried out using two karyological techniques referred to as the squash method and the protoplast method. The latter involves isolation of protoplasts from unfixed root meristems and provides mitotic images in which the chromosomes, conveniently dispersed and disposed on the same plane, are significantly longer, and better structured, than those obtained by the squash method. A critical analysis of this technique is carried out. The results of this study led us to propose a karyotype forNicotiana plumbaginifolia and to characterize each chromosome by mere morphological examination. This characterization was further detailed by C-banding.     

Inheritance of resistance to the root-knot nematode Meloidogyne arenaria in Myrobalan plum

The inheritance of resistance of the self-incompatible Myrobalan plum Prunus cerasifera to the root-knot nematode Meloidogyne arenaria was studied using first a diallel cross between five parents of variable host suitability (including two highly resistant clones P.1079 and P.2175, a moderate host P.2032, a good host P.2646 and an excellent host P.16.5), followed by the G2 crosses P.16.5 × (P.2646 × P.1079) and P.2646 × (P.16.5 × P.1079). A total of 355 G1 and 72 G2 clones obtained from hard-wood cuttings sampled from trees in the field experimental design, then rooted in the nursery and inoculated individually in containers (5–10 replicates per clone) under greenhouse conditions, were evaluated for their host suitability based on a 0–5 gall-index rating under a high and durable inoculum pressure of the nematode. In the crosses involving the resistant P.1079 and P.2175 and the hosts P.2646 and P.16.5: (1) all of the G1 crosses of P.1079 were resistant while the G2 crosses segregated 1 resistant to 1 host, (2) the G1 crosses between P.2175 and either P.2646 or P.16.5 segregated 1 resistant to 1 host, and (3) all of the G1 progeny between P.2646 and P.16.5 were host. These results indicate that resistance is conferred by a single major dominant resistance gene (homozygous) in P.1079, and the same, or an allelic or a different, major dominant gene (heterozygous) in P.2175, and that P.2646 and P.16.5 are recessive for this (these) major resistance gene(s). As expected according to the hypothesis of a recessive genotype for P.2032, all of its hybrids with P.1079 were resistant, all of its hybrids with P.2646 and P.16.5 were host, and its hybrids with P.2175 segregated for resistance. Nevertheless, the 32 segregation ratio of these latter hybrids suggests that clones bearing the P.2175 gene would have a selective advantage. Both resistance genes are completely dominant and confer a non-host behaviour that totally prevents the multiplication of the nematode. This is the first reported evidence of major nematode resistance genes towards M. arenaria in a species of the subgenus Prunophora in the genus Prunus. The symbols Ma1 for the P.2175 gene and Ma2 for the P.1079 gene are proposed.     

RAPD and SCAR markers linked to the Ma1 root-knot nematode resistance gene in Myrobalan plum (Prunus cerasifera Ehr.)

 The Myrobalan plum (Prunus cerasifera) is a self-incompatible species in which the clones P.2175, P.1079 and P.2980 are highly resistant to all root-knot nematodes (RKN), Meloidogyne spp. Each clone bears a single major dominant gene, designated Ma1, Ma2 and Ma3 respectively, that controls a high and wide-spectrum resistance. Bulked segregant analysis (BSA) and random amplified polymorphic DNA (RAPD) analysis were both performed to detect markers linked to the Ma1 gene using three segregating progenies from P.2175 (Ma1 ma1) crossed by three host parents (ma1 ma1). Four dominant coupling-phase markers were identified from a total of 660 10-base primers tested. The resulting linkage map spans 14.7 cM and comprises three markers located on the same side of Ma1 and one marker located on the other side. The nearest markers (OPAL19₇₂₀ and OPA16₁₄₀₀) are located at 3.7 and 6.7 cM, respectively, on each side of the gene. Among the three markers that could be successfully converted into sequence characterized amplified region (SCAR) markers, two of them (SCAL19₆₉₀ and SCAN12₆₂₀) were scored as dominant markers whereas the third (SCAO19₇₇₀) failed to produce any polymorphism. SCAL19, and to a lesser extent SCAN12, can be used reliably in the marker-assisted selection of Prunus rootstocks. These markers are adequate to identify the Ma1 RKN resistance gene in intraspecific segregating progenies and will be suitable for the creation of interspecific rootstocks involving Myrobalan plum. Some of the RAPD and SCAR markers for Ma1 were also recovered in clones P.1079 and P.2980, but not in additional host clones, suggesting that Ma1, Ma2 and Ma3 are either allelic or at least closely linked. Received: 22 September 1998 / Accepted: 19 December 1998     

Production of a cell wall-associated endopolygalacturonase by Colletotrichum lindemuthianum and pectin degradation during bean infection

The bean pathogen Colletotrichum lindemuthianum expresses two endopolygalacturonase genes, CLPG1 and CLPG2, during interaction with its host plant. However, only CLPG1 was found to be secreted to the extracellular medium during saprophytic growth of the fungus on pectin. To localize CLPG2, a FLAG epitope sequence was inserted in the C-terminal sequence of CLPG2 and the modified gene was introduced into C. lindemuthianum. Western blot analysis using a FLAG monoclonal antibody allowed the detection of CLPG2 in intracellular protein extracts and in the cell wall fraction, but not in the culture medium. Indirect immunofluorescence microscopy was performed to detect CLPG2 during saprophytic or parasitic growth. According to the expression pattern of CLPG2, it was found that CLPG2 accumulates in the fungal cell wall during growth on pectin medium and during appressorium formation, both in vitro and during interaction with the plant. Pectin degradation was not detected around the infection peg using the monoclonal antibody JIM7, specific for methyl-esterified galacturonan. However, extensive pectin dissolution was observed during the development of secondary hyphae.     

A reciprocal translocation between ’Garfi’ almond and ’Nemared’ peach

A map with 51 markers (46 RFLPs and five isozymes) was constructed using an interspecific F₂ population between ’Garfi’ almond (Prunus amygdalus Batsch.) and ’Nemared’ peach [Prunus persica (L.) Batsch.]. This map was developed by selecting markers covering most of the distance of the eight linkage groups from previously constructed Prunus maps. The markers studied in this population mapped to seven linkage groups instead of the eight expected in Prunus. Markers belonging to groups 6 and 8 in previous maps formed a single group in the ’Garfi’×’Nemared’ F₂ and several marker pairs placed in different groups in other maps exhibited tight linkages. The study of pollen fertility and chromosome behavior during meiosis in the F₁ generation allowed us to confirm the hypothesis that a reciprocal translocation exists between ’Garfi’ and ’Nemared’. Based on independent evidence of linkage between markers and pollen fertility data in the F₂ population, we concluded that the breakpoint of the reciprocal translocation was placed between markers AC50 and AG26A in group 6 and between markers AG112A and FG230A in group 8. Received: 28 June 2000 / Accepted: 17 October 2000     

Marker-assisted selection for the wide-spectrum resistance to root-knot nematodes conferred by the Ma gene from Myrobalan plum (Prunus cerasifera) in interspecific Prunus material

Prunus species express a more or less wide spectrum of resistance to root-knot nematodes (RKN) of the genus Meloidogyne. Among them, sources from Myrobalan plum (P. cerasifera) control all major and minor RKN species tested. In this outbreeding species, the clones P.2175 and P.2980 are heterozygous for the Ma single dominant gene and carry the alleles Ma1 and Ma3, respectively. Each allele confers a high-level resistance to the predominant RKN, M. arenaria, M. incognita and M. javanica and to the Florida isolate of an unknown Meloidogyne sp. which overcomes the resistance from peach and almond sources. The polymorphism of two coupling-phase SCAR markers tightly linked to Ma, SCAL19₆₉₀ and SCAFLP2₂₀₂, was evaluated within diverse diploid Prunus accessions. This material belongs to the subgenera Prunophora (Myrobalan and apricot) or Amygdalus (peach, almond and almond-peach) and includes the RKN resistance sources Nemared, Alnem 1 and GF.557. The alleles SCAL19₆₉₀ and SCAFLP2₂₀₂ were not present in three apricot cultivars (Moniqui, Luizet and Stark Early Orange) representative of the genetic diversity of this species and they segregated in an interspecific cross between P.2980 and apricot. These results suggest that apricot, reported as resistant to M. arenaria, M. incognita and M. javanica, and the Myrobalan plum might possess two different resistance systems. SCAL19₆₉₀ and SCAFLP2₂₀₂ were also absent from all tested Amygdalus material, whatever its resistance to RKN. Eight Myrobalan×Amygdalus segregating progenies including bispecific (P.2175 or P.2980×peach or almond) and trispecific (P.2175 or P.2980×almond-peach) hybrids were tested with the Florida isolate to identify individuals carrying the Ma resistance alleles. Both SCARs were then evaluated for segregation in these progenies to develop marker-assisted selection of Prunus interspecific rootstocks. SCAL19₆₉₀ and SCAFLP2₂₀₂ could be clearly detected and their tight linkage to Ma1 and Ma3 was confirmed. Consequently these SCARs appear to be powerful tools to screen for RKN resistance conferred by the Ma gene. They should also facilitate marker-assisted pyramiding of Ma with other resistance genes from the Amygdalus subgenus or from the botanically-related Armeniaca section.     

Differential Response to Root-Knot Nematodes in Prunus Species and Correlative Genetic Implications

Responses of 17 Prunus rootstocks or accessions (11 from the subgenus Amygdalus and 6 from the subgenus Prunophora) were evaluated against 11 isolates of Meloidogyne spp. including one M. arenaria, four M. incognita, four M. javanica, one M. hispanica, and an unclassified population from Florida. Characterization of plant response to root-knot nematodes was based on a gall index rating. Numbers of females and juveniles plus eggs in the roots were determined for 10 of the rootstocks evaluated against one M. arenaria, one M. incognita, one M. javanica, and the Florida isolate. These 10 rootstocks plus Nemaguard and Nemared were retested by growing three different rootstock genotypes together in containers of soil infested individually with each of the above four isolates. Garfi and Garrigues almonds, GF.305 and Rutgers Red Leaf peaches, and the peach-almond GF.677 were susceptible to all isolates. Differences in resistance were detected among the other rootstocks of the subgenus Amygdalus. The peach-almond GF.557 and Summergrand peach were resistant to M. arenaria and M. incognita but susceptible to M. javanica and the Florida isolate. Nemaguard, Nemared, and its two hybrids G x N no. 15 and G x N no. 22 were resistant to all but the Florida isolate. In the subgenus Prunophora, Myrobalan plums P.1079, P.2175, P.2980, and P.2984; Marianna plum 29C; and P. insititia plum AD.101 were resistant to all isolates. Thus, two different genetic systems of RKN resistance were found in the subgenus Amygdalus: one system acting against M. arenaria and M. incognita, and another system also acting against M. javanica. Prunophora rootstocks bear a complete genetic system for resistance also acting against the Florida isolate. The hypotheses on the relationships between these systems and the corresponding putative genes of resistance are presented.     

Translocation events demonstrated by molecular,in situ hybridization and chromosome pairing analyses in highly asymmetric somatic hybrid plants

Cytological analyses show rearranged chromosomes in some highly asymmetric nuclear hybrids obtained after fusion of mesophyll protoplasts ofNicotiana plumbaginifolia (wild type) with γ-irradiated (100 krad), kanamycin-resistant mesophyll protoplasts ofPetunia hybrida. Molecular, cytogenetic andin situ hybridization analyses performed on the asymmetric somatic hybrid P₁, previously identified as having a clearly metacentric chromosome besides a nearly completeNicotiana chromosome complement, are reported. Meiotic analysis andin situ hybridization experiments using ribosomal DNA as a probe showed that this metacentric chromosome represents a translocation of a chromosome fragment onto chromosome 9 ofN. plumbaginifolia. Southern hybridization with an rDNA probe showed that onlyNicotiana-specific rDNA was present.In situ hybridization experiments, using total genomic DNA ofP. hybrida as a probe, demonstrated that the translocated fragment representedPetunia DNA.     

The Collaborative Image of The City: Mapping the Inequality of Urban Perception

A traveler visiting Rio, Manila or Caracas does not need a report to learn that these cities are unequal; she can see it directly from the taxicab window. This is because in most cities inequality is conspicuous, but also, because cities express different forms of inequality that are evident to casual observers. Cities are highly heterogeneous and often unequal with respect to the income of their residents, but also with respect to the cleanliness of their neighborhoods, the beauty of their architecture, and the liveliness of their streets, among many other evaluative dimensions. Until now, however, our ability to understand the effect of a city''s built environment on social and economic outcomes has been limited by the lack of quantitative data on urban perception. Here, we build on the intuition that inequality is partly conspicuous to create quantitative measure of a city''s contrasts. Using thousands of geo-tagged images, we measure the perception of safety, class and uniqueness; in the cities of Boston and New York in the United States, and Linz and Salzburg in Austria, finding that the range of perceptions elicited by the images of New York and Boston is larger than the range of perceptions elicited by images from Linz and Salzburg. We interpret this as evidence that the cityscapes of Boston and New York are more contrasting, or unequal, than those of Linz and Salzburg. Finally, we validate our measures by exploring the connection between them and homicides, finding a significant correlation between the perceptions of safety and class and the number of homicides in a NYC zip code, after controlling for the effects of income, population, area and age. Our results show that online images can be used to create reproducible quantitative measures of urban perception and characterize the inequality of different cities.