罗非鱼类立克次氏体病的组织病理学观察

本文主要研究感染类立克次氏体(Rickettsia-like organism,RLO)的养殖罗非鱼(Oreochromis aureus♂×Oreochromis niloticus♀)肝、脾、肾、肠、鳃和心脏的组织病理变化。感染类立克次氏体的罗非鱼各器官广布粗糙不圆整的白色小结节,这些结节为肉芽肿坏死灶,分层不典型,与周围健康组织的界限不甚明显;严重病变的组织坏死区域较大,与周围明显增生的细胞形成清晰的巨大"肉瘤"状肿物。经吉姆萨-瑞氏染色后,在病变组织内,尤其是脾肾组织的巨噬细胞胞质内可见蓝紫色球状或颗粒样、成簇分布的类立克次氏体。这些发现可为罗非鱼类立克次氏体病的病理学诊断提供依据。     

The Brucella genome at the beginning of the post-genomic era

The year 2002 began with the publication of the first complete genome sequence for a Brucella species, that of the two replicons of B. melitensis 16M. Hopefully in 2002, the complete genome of B. suis 1330, and, perhaps, a B. abortus strain will be published. This is the culmination of over 30 years investigation of the composition, structure, organisation and evolution of the Brucella genome. Brucella research must now adapt to the new challenges of the post-genomic era.     

Herbicide-tolerant crops—real farmer opportunity or potential environmental problem?

Classical breeding, in-vitro selection and genetic engineering techniques have produced herbicide-tolerant crops. Commercial adoption of these cultivars in North America provides tolerance predominantly to non-selective herbicides for novel weed-control strategies. Of special value is the integration of these crops in minimum tillage situations, maintaining of a wide range of herbicides with different modes of action to provide a variety of opportunities for weed-control management. Associated with these special crops are a series of environmental issues which at present limit the rate of commercial development in Europe. Unlike the successful performance of herbicide tolerance in the crops, these strategic issues are much more difficult to resolve for technical, political, ethical and moral reasons. The primary concerns are the feasibility of controlling the volunteer crop and the opportunity for indiscriminate introgression of the herbicide-tolerance gene into agricultural and natural ecosystems. It is unlikely that these questions will be resolved without scaling-up field experiments to include the detection of herbicide-tolerance genes. The economic and management implications of herbicide-tolerant crops require special consideration in view of the necessity to integrate conventional and transgenic crops in new cropping systems. © 1998 SCI     

Sexual hybridisation in crosses of cultivated Brassica species with the crucifers Erucastrum gallicum and Raphanus raphanistrum: Potential for gene introgression

Studies were conducted to investigate the crossability of the cultivated Brassica species, Brassica napus (oilseed rape), B. rapa (turnip rape), and B. juncea (brown and oriental mustard), with two related cruciferous weeds that are abundant in certain regions of Canada, Erucastrum gallicum (dog mustard) and Raphanus raphanistrum ssp. raphanistrum (wild radish). Seed was produced without recourse to embryo rescue from all reciprocal crosses except R. raphanistrum × B. juncea. Four hybrid plants were recovered, namely B. napus × E. gallicum, B. napus × R. raphanistrum (two plants), and B. rapa × E. gallicum. The hybrids were characterized by their morphology, RAPD analysis, and cytological examination. The B. rapa × E. gallicum hybrid was extremely vigourous and fertile, and would likely grow in natural habitats. This hybrid produced self-seed and backcrossed readily with the B. rapa parent and, to a lesser extent, with the E. gallicum parent. The B. napus × E. gallicum hybrid was a weak plant, but produced fertile backcross progeny with the E. gallicum parent. The B. napus × R. raphanistrum hybrids were vigourous but mostly sterile. Because of their low vigour and/or sterility, hybrids produced from crosses of B. napus with the cruciferous weeds would not likely be an environmental concern. However, the potential of the B. napus × E. gallicum and B. rapa × E. gallicum hybrids to backcross with E. gallicum may be of concern. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of the gene pools of Triticum turgidum ssp. dicoccoides and Aegilops squarrosa for the breeding of common wheat (T. aestivum), through chromosome-doubled hybrids

Summary Triticum turgidum ssp. dicoccoides (wild emmer wheat, AABB, 2n=28) and Aegilops squarrosa (goat grass, DD, 2n=14) comprise a rich reservoir of valuable genetic material, which could be useful for the breeding of common wheat (T. aestivum, AABBDD, 2n=42). Many accessions of both wild species, most of them selected for resistance to stripe rust, were used to make amphiploids. Two strategies were applied: (1) the production of autopolyploid cytotypes of the wild species, followed by hybridisation, and (2) the production of allotriploid interspecific hybrids, followed by doubling of the number of chromosomes. The first route was unsuccessful because of failure of the crosses between the autopolyploid cytotypes, possibly due to incongruity between the two species and to reduced fertility in the autopolyploid cytotypes. The second route yielded the desired synthetic hexaploids. However, the rate of success of the crosses was low and there were great differences between years, and within years between crosses. Embryo rescue was applied to obtain the primary hybrids (2n=21), which were highly sterile and had on average 0.3 bivalents and 20.4 univalents per pollen mother cell. Various abnormalities were recorded. Doubling of the number of chromosomes sometimes occurred spontaneously or was brought about by colchicine treatment. The large scale of the interspecific hybridisation programme ensured that one-third of the female and one-sixth of the male accessions were represented in the synthetic hexaploids.     

Interspecific hybridisation betweenLimonium perigrinum Bergius andLimonium purpuratum L.

Summary Interspecific hybrids betweenLimonium perigrinum andL. purpuratum were obtained usingL. perigrinum as the female parent. No hybrids were produced by the reciprocal cross. Twelve- to 15-day-old embryos were rescued and cultured within their embryo sacs on modified B5 or KM medium. After two to three days the embryos were excised from their embryo sacs and re-plated on to fresh medium. When the embryo-derived plantlets had attained a length of 1 cm they were transferred to a modified MS medium containing BA and NAA for shoot proliferation. Plantlets were transferred to modified MS medium supplemented with IBA for 24 hours for root initiation then to a modified growth-regulator-free MS medium for root growth. After a further 28 days the plantlets were transferred to soil-less medium for acclimatisation. The hybrid characteristics of one of the 15 embryo-derived plants were determined by flow cytometry and by examination of morphological features. The mean DNA contents of 2C nuclei fromL. perigrinum, the hybrid andL. purpuratum were 13.98 pg, 16.81 pg and 19.37 pg, respectively. Mitotic and meiotic chromosome counts fromL. perigrinum andL. purpuratum showed that both parents and their hybrids had identical chromosome numbers (2n=24), and that the species were closely related. Morphological analyses of leaves and flowers showed that the hybrids displayed a number of features intermediate between both parents.Abbreviations B5 Gamborg et al. (1968) B5 medium - BA benzyl adenine - IBA indole-3-butyric acid - KM Kao and Michayluk (1975) medium - MS Murashige and Skoog (1962) medium - NAA napthalene-1-acetic acid - PVP polyvinylpyrrolidone     

Identification of barriers to interspecific crosses in the genus Trifolium

Summary A study of pre- and post-fertilisation barriers after interspecific crosses of diploid and tetraploid Trifolium pratense L. and wild species T. alpestre L., T. medium L. and T. sarosiense Hazsl. was aimed at finding of a promising cross combination for obtaining hybrids. The growth of pollen tubes was arrested in interspecific crosses mainly when T. pratense was at a diploid level. To investigate the post-fertilisation barriers in detail, the hybrid embryo viability was traced by two clearing treatments of immature seeds: (1) using chloral hydrate (which proved to be most appropriate); and (2) a mixture of benzyl benzoate and dibutly phthalate. In interspecific combinations T. pratense (4×) × either T. alpestre or T. sarosiense, enlargement of immature seeds occurred, but no hybrid embryo was traced. Of the wild species used as a male parent for crosses, T. medium was the only exception from the point of view of fertilisation. Globular, heart and the early torpedo stages of hybrid embryos were observed 7 days after pollination (DAP) but only when T. pratense was at a tetraploid level. When T. pratense (2×, 4×) was used as a male parent for interspecific crosses with T. alpestre, T. medium and T. sarosiense, strong defects in various stages of embryogenesis were observed, particularly wrinkled and narrowing embryo sacs caused by an expansion of endothelial cells. We conclude with the following finding: (1) to make crosses only in one direction with T. pratense as a female parent and T. medium as a male; (2) to use tetraploid plants of T. pratense; (3) and to excise hybrid embryos at an early torpedo stage, about 7 DAP.     

Development and cytogenetic characterisation of a double goat grass-barley chromosome substitution in tritordeum

×Tritordeum (Ascherson et Graebner, an amphiploid between Triticum turgidum conv. durum and Hordeum chilense), and chromosome substitution lines of tritordeum where chromosomes 2 H ^ch or 3 H ^ch H. chilense were replaced with chromosome 2 D of T. aestivum or 3 H ^v chromosome of H. vulgare, respectively, were used to assess the effect of specific chromosomes on the rachis. ×Tritordeum has brittle rachis while the 2 D(2 H ^ch) and 3 H ^v (3 H ^ch) substitution lines have non-brittle rachis. Both lines also have compact spikes, a character highly desirable for the improvement of tritordeum threshability. Different combinations of 2 D and 3 H ^v translocations were developed in tritordeum. In this article we present information on the identification and characterisation of all these introgression lines by the fluorescent in situ hybridisation.     

Inheritance in Solanum aethiopicum,the scarlet eggplant

Summary Analyses of F₁ and F₂ hybrid progenies from crosses between the ancestral species Solanum anguivi and cultivars of its domesticated derivative S. aethiopicum, have proved the mode of inheritance of prickles, stellate hairs and some other morphological characters and suggested the mode for several more. Most wild-type traits were dominant: many recessive domesticated traits involved imperfect morphogenesis suggesting loss of genetic control. F₁ hybrids between cultivars show marked heterosis and are recommended for crop production.     

Pink‐awned weedy rice (Oryza sativa): a potential conduit for gene exchange in rice agro‐ecosystems

Hybridisation between genetically distinct lineages results in increases in overall genetic diversity and is a potential mechanism for the origin and spread of adaptive alleles. Weed and crop hybridisation may result in weedy ecotypes, which have, in addition to classic weedy traits such as seed shattering and long seed dormancy, crop traits that enhance weediness, such as adaptation to field cultivation and harvest strategies. Weedy rice (Oryza sativa) hybridises with cultivated rice and, in the process, may produce new (pink‐awned) weedy rice varieties. Pink‐awned (PA) weedy rice plants have been observed in rice fields in Arkansas. We explored the genetic relationships between PA weedy rice, crop rice, global rice accessions and other weedy rice ecotypes present in the southern United States. Gene sequencing of 48 sequence‐tagged sites (STS loci) revealed a pattern of hybridisation and gene flow between blackhull weedy rice and tropical japonica rice (O. sativa subsp. japonica) cultivars. Our data suggest that PA rice originates from hybridisation between blackhull weedy rice and tropical japonica rice. PA rice offspring segregate phenotypic traits associated with weediness in rice. This segregation could lead to adaptive allele combinations in PA rice, which could potentially move into other weedy rice types through subsequent hybridisation events.