探讨种间传粉在杜鹃花属自然杂交物种形成中的作用

自然杂交是物种形成的一个途径, 在植物进化中起着重要的作用。自然杂交主要通过种间的基因交流, 花粉传递则是基因交流的主要途径。马缨花(Rhododendron delavayi)、大白花杜鹃(R. decorum)、迷人杜鹃(R. agastum)和露珠杜鹃(R. irroratum)是在云南广泛分布的杜鹃花种类, 马缨花与大白花杜鹃形态上区别明显, 而它们的可能杂交种迷人杜鹃和露珠杜鹃在形态上基本介于二者之间。本文对这4种杜鹃花的开花物候和访花昆虫的种类进行了观察,并进行了其繁育系统和种子萌发的实验。我们发现马缨花的花期从3月初至5月底, 迷人杜鹃与露珠杜鹃花期基本一致, 为3月初至4月初, 二者同大白花杜鹃基本不存在花期重叠, 大白花杜鹃的花期为4月中旬至5月底。4种杜鹃花的开花期不同年份稍有变化, 其单花开花周期都在一周以上。4种杜鹃花的传粉昆虫虽然种类和数量上有所不同, 但都以膜翅目和双翅目昆虫为主, 中华蜜蜂(Apis cerana cerana)是其共有的传粉昆虫。繁育系统研究发现, 除露珠杜鹃外, 其余3种自花不育, 而种间杂交不存在任何生殖障碍, 可以产生萌发率很高的种子。通过分析4种杜鹃花开花物候重叠、共有传粉昆虫及种间杂交可育等现象, 探讨了传粉昆虫和异花授粉的机制在自然杂交物种形成中的作用及杂交种的适应能力。     

Morphological and molecular evidence of natural hybridization between two distantly related Rhododendron species from the Sino-Himalaya

Rhododendron (Ericaceae) is a large woody genus in which hybridization may play an important role in evolution and speciation, particularly in the Sino-Himalayan region, where many interfertile species often occur sympatrically. Natural hybridization between Rhododendron delavayi Franch. (=  R. arboreum ssp. delavayi ) and Rhododendron decorum Franch., which belong to different subsections of subgenus Hymenanthes, was investigated. Material of R. delavayi and R. decorum and their putative hybrids was collected from the wild. On the basis of morphology, chloroplast DNA, nuclear ribosomal DNA, and AFLP profiles, hybrids and parental species were identified. Hybridization occurred in both directions, but was asymmetrical, with R. delavayi as the major maternal parent in the hybrid zone. Most of the hybrids possessed intermediate phenotypes, and amongst the 15 hybrids detected were six F1s, two F2s, one first-generation backcross to R. delavayi , and two first-generation backcrosses to R. decorum . This indicates that, if Rhododendron underwent rapid radiation in this region, it did so in spite of permeable species barriers.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 119–129.     

Natural Hybridization between Rhododendron delavayi and R. cyanocarpum (Ericaceae), from Morphological, Molecular and Reproductive Evidence

The natural hybridization that occurs between two sympatric species of Rhododendron subgenus Hymenanthes in Yunnan, China, was investigated. In field observations, it was noted that the putative hybrids between R. delavayi Franch. and R. cyanocarpum (Franch.) Franch. ex W.W. Sm. had intermediate morphologies. On the basis of morphology, chloroplast DNA (trnL-rpl32) and nuclear DNA (waxy), hybrids and parental species were identified. Hybridization occurred in both directions, but was asymmetrical, with R. delavayi as the major maternal parent. Reciprocal hand pollination treatments showed that either species, as pollen donor or pollen receiver, could produce fruits. It was noted that fruit set varied among treatments. The same pollinators (bumblebees) were shared in both parental species. From these results, we conclude that individuals with intermediate morphologies are indeed of hybrid origin from natural hybridization between R. cyanocarpum and R. delavayi. Furthermore, we presume the hybridization at the study site could have been initiated by habitat disturbance in the 1950s, and we may hence witness the early stages of hybrid swarm formation.     

Natural hybridization of Japanese <Emphasis Type="Italic">Rhododendron</Emphasis> section <Emphasis Type="Italic">Brachycaryx</Emphasis> in Mount Kintoki in eastern Japan and concerns for genetic diversity in restoring their habitat

Native Rhododendrons section Brachycaryx in eastern Japan are decreasing in their natural habitats and the need to restore these habitats is increasing. Conservation of genetic diversity in restoring habitat requires clarification of the balance of interspecies genetic exchange which occurs in their natural habitats. In well-preserved natural habitats of Rhododendron dilatatum, R. kiyosumense, and R. wadanum and their natural hybrids R.×kuratanum and R.×hasegawai we investigated their geographical distribution, frequency, and flowering period. DNA analysis of the internal transcribed spacer (ITS) region was also conducted to confirm the species related to hybridization. Our findings in the field survey were: (1) Hybridizations occur in the overlap zones of related species. (2) R.×hasegawai occurs more frequently than R.×kuratanum, probably because the flowering seasons of R. kiyosumense and R. wadanum overlap longer than those of R. dilatatum and R. kiyosumense. (3) Natural hybrid occurrence is, nevertheless, under 9% of all related Rhododendrons section Brachycalyx. Analysis of the ITS region suggested that the two hybrids are generated from interspecific gene exchange, i.e., (4) R. dilatatum and R. kiyosumense relate to the formation of R.×kuratanum. (5) R.×hasegawai is a hybrid of R. wadanum and some species other than R. wadanum. On the basis of these findings we delineated several guidelines for restoring habitats of Rhododendrons of Section Brachycaryx with concerns for genetic diversity: (1) Before use, identify plant materials by morphological traits to determine whether they are original species or hybrids. (2) Investigate the distribution of remnant Rhododendrons section Brachycaryx before restoration. (3) Combine plant materials of original species in the natural distribution.     

Hybridization and asymmetric introgression between <Emphasis Type="Italic">Rhododendron eriocarpum</Emphasis> and <Emphasis Type="Italic">R. indicum</Emphasis> on Yakushima Island,southwest Japan

We examined natural hybridization between two morphologically and ecologically divergent species on Yakushima Island-the light-purple flowered Rhododendron eriocarpum native to seaside habitats and the red flowered R. indicum native to riverside habitats. By investigation of morphological traits and amplified fragment length polymorphisms (AFLP) we found that hybrid individuals morphologically and genetically intermediate between the two species grow mainly in the seaside areas of the island. The degree of morphological and genetic variation was different among the seaside hybrid populations. Although most pollinator species were exclusive to one of the two flower color groups, the halictine bees of Lasioglossum were observed in both the color types. The crucial interspecific incompatibility after pollination has not been previously described. Geographic distance between the populations is likely to be an important primary factor in bringing about natural hybridization and determining the degree of introgression between R. eriocarpum and R. indicum. The fact that hybrids occur mostly in the seaside area on Yakushima Island indicates that asymmetrical introgression occurs from R. indicum to R. eriocarpum. Alternatively, strong habitat-mediated selection from recurrent floods may prevent the hybrids from colonizing riverside habitats.     

Confirmation of natural hybrids between Gentiana straminea and G. siphonantha (Gentianaceae) based on molecular evidence

A few individuals with intermediate morphology always appeared in the sympatric distributions of Gentiana straminea and G. siphonantha. These intermediate individuals were hypothesized to be the hybrids of two species after a careful evaluation of their morphological characteristics. To test this hypothesis, sequence comparison of the internal transcribed spacer (ITS) regions of the nuclear ribosomal and trnS (GCU)-trnG (UCC) intergenic spacer region of the chloroplast DNA from Gentiana straminea, G. siphonantha and the putative hybrids was performed. The results suggest that most intermediate individuals were the natural hybrids between G. straminea and G. siphonantha. In addition, we examined the sequence variation among the individuals of both parent species and analyzed the possibility leading to the incongruent identification in some individuals based on morphologic and molecular evidences, respectively. The intraspecific diversification of DNA fragments within both parent species and their high variability in hybrid swarms probably resulted from chloroplast genome recombination and incomplete lineage sorting during the early stages of speciation origin of the parent species. __________ Translated from Acta Botanica Yunnanica, 2007, 29 (1): 91–97 [译自:云南植物研究]     

四川杜鹃花属三个新异名

将我国四川杜鹃花属Rhododendron L.植物2个种和1个亚种（R.decorum Franch. ssp.cordatum Hu,R.xichangense Z.J.Zhao及R.davidsonianum Rehd.&Wils.）处理为新异名,并作了相应的讨论。     

哀牢山兜兰,中国兰科一新天然杂种

报道了中国云南省兰科（Orchidaceae）兜兰属（Paphiopedilum）一新天然杂交种：哀牢山兜兰（Paphiopedilum×ailaoshanense B. Liu & S. P. Chen）。哀牢山兜兰与白旗兜兰（P. spicerianum）和沧源兜兰（P. gratrixianum var. cangyuanense）近缘,与前者的区别在于哀牢山兜兰花梗和子房有毛,中萼片带紫色晕以及紫色斑点,花瓣上侧暗绿色带紫色晕,下侧黄绿色;与后者的区别在于中萼片具1条宽阔的紫褐色中带,退化雌蕊紫色。哀牢山兜兰与天然杂种泸水兜兰（Paphiopedilum×lushuiense）相似,而哀牢山兜兰的中萼片下部边缘不后卷,近基部具紫红色晕,合萼片具2条明显紫色粗脉,花瓣匙形,上边缘波状,长6.0~6.2 cm,唇瓣长5.0~5.5 cm。为厘清哀牢山兜兰,沧源兜兰及白旗兜兰之间的关系,基于3个叶绿体基因片段（matK、rbcL、trnL）,构建了兜兰属部分植物系统发育树。鉴于形态和分子数据,认为哀牢山兜兰是天然杂交种。凭证标本存放于福建农林大学标本馆。     

Revised treatment of <Emphasis Type="Italic">Memecylon</Emphasis> sect. <Emphasis Type="Italic">Afzeliana</Emphasis> (<Emphasis Type="Italic">Melastomataceae: Olisbeoideae</Emphasis>), including three new species from Cameroon

Summary  Seven new names at species rank are proposed in Memecylon sect. Afzeliana Jacq.-Fél., a group of forest shrubs and small trees confined to Guineo-Congolian Africa. The group is centred in Cameroon, where 17 of the 20 species occur. A new flower type, the “star-flower” in Memecylon is revealed, and its taxonomic and ecological importance discussed. Three new, locally endemic species from the South West Province of Cameroon are described, mapped and illustrated: M. kupeanum R. D. Stone, Ghogue & Cheek, M. bakossiense R. D. Stone, Ghogue & Cheek, and M. rheophyticum R. D. Stone, Ghogue & Cheek. Two new names, M. accedens R. D. Stone, Ghogue & Cheek and M. hyleastrum R. D. Stone & Ghogue and one new combination, M. mamfeanum (Jacq.-Fél.) R. D. Stone, Ghogue & Cheek are provided at species level for three taxa originally proposed as varieties of M. afzelii G. Don. The taxon M. arcuatomarginatum var. simulans Jacq.-Fél. is also elevated to species status, as M. simulans (Jacq.-Fél.) R. D. Stone & Ghogue. Conservation assessments are provided for all the newly named taxa. A key is provided to the species of Memecylon sect. Afzeliana.     

A simple chromosomal marker can reliably distinguishes <Emphasis Type="Italic">Poncirus</Emphasis> from <Emphasis Type="Italic">Citrus</Emphasis> species

Several chromosome types have been recognized in Citrus and related genera by chromomycin A₃ (CMA) banding patterns and fluorescent in situ hybridization (FISH). They can be used to characterize cultivars and species or as markers in hybridization and backcrossing experiments. In the present work, characterization of six cultivars of P. trifoliata (“Barnes”, “Fawcett”, “Flying Dragon”, “Pomeroy”, “Rubidoux”, “USDA”) and one P. trifoliata × C. limonia hybrid was performed by sequential analyses of CMA banding and FISH using 5S and 45S rDNA as probes. All six cultivars showed a similar CMA⁺ banding pattern with the karyotype formula 4B + 8D + 6F. The capital letters indicate chromosomal types: B, a chromosome with one telomeric and one proximal band; D, with only one telomeric band; F, without bands. In situ hybridization labeling was also similar among cultivars. Three chromosome pairs displayed a closely linked set of 5S and 45S rDNA sites, two of them co-located with the proximal band of the B type chromosomes (B/5S-45S) and the third one co-located with the terminal band of a D pair (D/5S-45S). The B/5S-45S chromosome has never been found in any citrus accessions investigated so far. Therefore, this B chromosome can be used as a marker to recognize the intergeneric Poncirus × Citrus hybrids. The intergeneric hybrid analyzed here displayed the karyotype formula 4B + 8D + 6F, with two chromosome types B/5S-45S and two D/5S-45S. The karyotype formula and the presence of two B/5S-45S chromosomes clearly indicate that the plant investigated is a symmetric hybrid. It also demonstrates the suitability of karyotype analyses to differentiate zygotic embryos or somatic cell fusions involving trifoliate orange germplasm. During the submission of this paper, we analyzed 25 other citrus cultivars with the same methodology and we found that the chromosome marker reported here can indeed distinguish Poncirus trifoliata from grapefruits, pummelos, and one variegated access of Citrus, besides the previously reported access of limes, limons, citrons, and sweet-oranges. However, among 14 mandarin cultivars, two of them displayed a single B/5S-45S chromosome, whereas in Citrus hystrix D.C., a far related species belonging to the Papeda subgenus, this chromosome type was found in homozygosis. Since these two mandarin cultivars are probably of hybrid origin, we assume that for almost all commercial cultivars and species of the subgenus Citrus this B type chromosome is a useful genetic marker.     

Genetic analysis of the position of meiosis in <Emphasis Type="Italic">Porphyra haitanensis</Emphasis> Chang et Zheng (Bangiales,Rhodophyta)

Crossing experiments were carried out between artificial pigmentation mutants and the wild type in Porphyra haitanensis Chang et Zheng to ascertain where meiosis occurs in its life history by confirming whether the color segregation and the color-sectored blades appear in F₁ gametophytic blades developed from conchospores which are released from heterozygous conchocelis. Two red-type pigmentation mutants (R-10 and SPY-1) were used as the female parent. Their blades are red or red orange in color, thinner than the wild type and weak in elasticity, and have no denticles on their margins. The wild type (W) was used as the male parent; its blades are light brown in color, thick and good in elasticity, and have many marginal denticles. The F₁ gametophytic blades developed from conchospores which were released from heterozygous conchocelis produced in the crosses of R-10(♀)×W(♂) and SPY-1(♀)×W(♂) showed two parental colors (R and W) and two new colors (R', lighter in color than R; W', wild-type-like color and redder than W). Linear segregation of colors occurred in the F₁ blades, forming color-sectored blades with 2–4 sectors. In the color-sectored blades, R and R' sectors were thinner than W and W' sectors, and had weak elasticity and no denticles on their margins, whereas W and W' sectors were thick and had good elasticity and many marginal denticles. Of the F₁ gametophytic blades, 95.2–96.7% were color-sectored and only 3.3–4.8% were unsectored. These results indicate that meiosis of P. haitanensis occurs during the first two cell divisions of a germinating conchospore, and thus it is considered that the initial four cells of a developing conchosporeling constitute a linear genetic tetrad leading to the formation of a color-sectored blade. The new colors of R' and W' were recombinant colors due to the chromosome recombination during the first cell division in meiosis. It is considered that color phenotypes of the two mutants used in this paper were result of two (or more) recessive mutations in different genes, and that they also have mutations concerned with blade thickness and formation of marginal denticles, which are linked with the color mutations.     

<Emphasis Type="Italic">Warneckea austro-occidentalis</Emphasis>, a new species from Cameroon and Nigeria,and re-evaluation of <Emphasis Type="Italic">W. fascicularis</Emphasis> var. <Emphasis Type="Italic">mangrovensis</Emphasis> (Melastomataceae-Olisbeoideae)

Summary  Described and illustrated is Warneckea austro-occidentalis R. D. Stone, an endemic of tropical forests in Cameroon’s South West Province and adjacent Nigeria. The name W. mangrovensis (Jacq.-Fél.) R. D. Stone is also proposed at species level for the taxon originally described as W. fascicularis var. mangrovensis Jacq.-Fél. An IUCN (2001) status of endangered is assigned for both W. austro-occidentalis and W. mangrovensis.     

Morphological and molecular characterization of a natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae)

A putative natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae) from southern Italy, formerly known asO. alata, was characterized both on morphological and molecular grounds in order to confirm its hybrid status and to trace its maternal lineage. The morphological characters of the putative hybrid showed intermediacy between those of the parent species, and restriction fragment length polymorphism (RFLP) analysis of a region of the nuclear ribosomal DNA confirmed its hybrid origin. Chloroplast DNA RFLP analysis indicated thatO. morio provided the maternal genome.     

Reticulate hybridization of <Emphasis Type="Italic">Alpinia</Emphasis> (Zingiberaceae) in Taiwan

Reticulate hybridization is a complicated and creative mechanism in plant evolution that can cause interference in phylogenetic studies. Based on observations of intermediate morphology, low pollen fertility, and overlapping distributions of putative parent species, Yang and Wang (Proceedings of the cross-strait symposium on floristic diversity and conservation. National Museum of Natural Science, Taichung, Taiwan, pp 183–197, 1998) first proposed reticulate hybridization of Alpinia in Taiwan. In the present study, molecular tools were used to explore relationships between four parental species and their homoploidy hybrids, and the impact of hybridization on phylogeny reconstruction. Based on DNA markers, maternal heritance of the chloroplast genome, and additivity of nuclear ribosomal internal transcribed spacer, the present results provide strong support for the hybridization hypothesis. Co-existence of parental ribotypes within hybrids revealed that these hybridization events were current, while reciprocal and introgressive hybridization were inferred from chloroplast DNA data. Furthermore, iterative hybridizations involving more than two parental species may occur in notorious hybrid zones. Ecological, phenological, and physiological evidence provides insight into why such frequent hybridization occurs in Taiwanese Alpinia. In the phylogenetic tree of the Zerumbet clade reconstructed in this study, the chloroplast sequences from one hybrid species were not grouped into a subclade, implying instability caused by hybridization. Failure to find morphological apomorphies and biogeographical patterns in this clade was likely partially due to reticulate hybridization. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Discovery of species-wide EST-derived markers in Rhododendron by intron-flanking primer design

From two cDNA libraries made of flowers of the evergreen Rhododendron simsii hybrid ‘Flamenco’ and the deciduous species Rhododendron luteum, 323 cDNA fragments were randomly sequenced and functions were assigned. Reliable homologies were found for 31% of the fragments. For mapping applications, EST-derived markers were developed on 127 sequences. Since polymorphisms are more prone to come about in introns, primers were selected to have an elevated probability to be intron-spanning. The utilised approach resulted in an overall polymorphism-generating efficiency of 35% (45 polymorphic markers). The transferability of these cDNA-based EST markers among plant species was confirmed within the Rhododendron genus. The markers developed here are currently screened for the construction of genetic linkage maps of four crossing populations of R. simsii hybrids.     

Genetic discrimination of middle Mississippi River <Emphasis Type="Italic">Scaphirhynchus</Emphasis> sturgeon into pallid,shovelnose, and putative hybrids with multiple microsatellite loci

The pallid sturgeon (Scaphirhynchus albus), which is protected under the US endangered species act, and shovelnose sturgeon (S. platorhynchus), which is legally harvested in some locations, are sympatric throughout the range of pallid sturgeon. There is considerable morphological overlap between the species making discrimination problematic. The inability to reliably differentiate between species across all life stages has hampered pallid sturgeon recovery efforts. Furthermore, the two species are believed to hybridize. This study used allele frequency data at multiple microsatellite loci to perform Bayesian and likelihood-based assignment testing and morphological measures and meristics to discriminate pallid, shovelnose, and putative hybrid sturgeons from the middle Mississippi River. Bayesian model-based clustering of the genetic data indicated that two natural genetic units occur in the region. These units correspond to morphologically identified pallid and shovelnose sturgeon. Some individuals were morphologically intermediate and many of these failed to strongly assign genetically as either pallid or shovelnose sturgeon, suggesting they may be hybrids. These data indicate that pallid sturgeon and shovelnose sturgeon are genetically distinct in the middle Mississippi River (F _ST = 0.036, P < 0.0001) and suggest that hybridization between pallid sturgeon and shovelnose sturgeon has occurred in this region with genetic distance estimates indicating the greatest distance is between pallid and shovelnose sturgeon, while hybrid sturgeon are intermediate but closer to shovelnose. This study demonstrates that assignment testing with multiple microsatellite markers can be successful at discriminating pallid sturgeon and shovelnose sturgeon, providing a valuable resource for pallid sturgeon recovery and conservation.

Identification of Diploid <Emphasis Type="Italic">Stylosanthes seabrana</Emphasis> Accessions from Existing Germplasm of <Emphasis Type="Italic">S. scabra</Emphasis> Utilizing Genome-Specific STS Markers and Flow Cytometry,and Their Molecular Characterization

Stylosanthes seabrana (Maass and ‘t Mannetje) (2n = 2x = 20), commonly known as Caatinga stylo, is an important tropical perennial forage legume. In nature, it largely co-exist with S. scabra, an allotetraploid (2n = 4x = 40) species, sharing a very high similarity for morphological traits like growth habit, perenniality, fruit shape and presence of small appendage at the base of the pod or loment. This makes the two species difficult to distinguish morphologically, leading to chances of contamination in respective germplasm collections. In present study, 10 S. seabrana accessions were discovered from the existing global germplasm stock of S. scabra represented by 48 diverse collections, utilizing sequence-tagged-sites (STS) genome-specific markers. All the newly identified S. seabrana accessions displayed STS phenotypes of typical diploid species. Earlier reports have conclusively indicated S. seabrana and S. viscosa as two diploid progenitors of allotetraploid S. scabra. With primer pairs SHST3F3/R3, all putative S. seabrana yielded single band of ~550 bp and S. viscosa of ~870 bp whereas both of these bands were observed in allotetraploid S. scabra. Since SHST3F3/R3 primer pairs are known to amplify single or no band with diploid and two bands with tetraploid species, the amplification patterns corroborated that all newly identified S. seabrana lines were diploid in nature. Flow cytometric measurement of DNA content of the species, along with distinguishing morphological traits such as flowering time and seedling vigour, which significantly differ from S. scabra, confirmed all identified lines as S. seabrana. These newly identified lines exhibited high level of similarity among themselves as revealed by RAPD and STS markers (>92% and 80% respectively). Along with the enrichment in genetic resources of Stylosanthes, these newly identified and characterized accessions of S. seabrana can be better exploited in breeding programs targeted to quality.     

<Emphasis Type="Italic">Colletotrichum echinochloae</Emphasis>, a new species on Japanese barnyard millet (<Emphasis Type="Italic">Echinochloa utilis</Emphasis>)

Five isolates of a species of Colletotrichum were collected from Japanese barnyard millet (Echinochloa utilis) in Japan. Although the fungus had once been identi-fied as C. graminicola sensu lato, it was clearly different from C. graminicola isolated from maize (Zea mays) in its falcate and short conidia, 18.0–22.2 μm in length, cultural characteristics, and specific pathogenicity to E. utilis. Moreover, molecular phylogenetic analyses using sequences of rDNA-ITS, HMG, and SOD2 indicated a monophyly of the isolates. A new species, Colletotrichum echinochloae, is then proposed based on the morphological, pathological, and molecular characteristics.     

Use of RAPD in differentiation of selected species of <Emphasis Type="Italic">Sargassum</Emphasis> (Sargassaceae,Phaeophyta)

Sargassum C. Agardh is one of the most common but little understood genera of Phaeophyta in Malaysia. The difficulty in species delineation is due to morphological plasticity. A combination of morphology and random amplified polymorphic DNA (RAPD) studies of selected Sargassum species was carried out to have a better understanding of the taxonomy. Primer OPA13 was found to be good for discriminating between Sargassum species. Sargassum binderi was shown to be different from S. oligocystum (S_D>0.5 = 14.11%), indicating the importance of the vesicle and receptacle in species differentiation. S. baccularia was clearly separated out from S. polycystum and S. stolonifolium using primer OPA13. RAPD analysis showed that the presence of the stolon is an important character for separating S. baccularia (no stolon) from S. polycystum (stolon) and S. stolonifolium (stolon). Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Reduction of Selenite to Elemental Red Selenium by <Emphasis Type="Italic">Rhizobium</Emphasis> sp. Strain B1

A bacterium that reduces the soluble and toxic selenite anion to insoluble elemental red selenium (Se⁰) was isolated from a laboratory bioreactor. Biochemical, morphological, and 16S rRNA gene sequence alignment identified the isolate as a Rhizobium sp. that is related to but is genetically divergent from R. radiobacter (syn. Agrobacterium tumefaciens) or R. rubi (syn. A. rubi). The isolate was capable of denitrification and reduced selenite to Se⁰ under aerobic and denitrifying conditions. It did not reduce selenate and did not use selenite or selenate as terminal e⁻ donors. Native gel electrophoresis revealed two bands, corresponding to molecular weights of ∼100 and ∼45 kDa, that reduced selenite. Tungsten inhibited in vivo selenite reduction, suggesting that a molybdenum-containing protein is involved in selenite reduction. This organism, or its enzymes or DNA, might be useful in bioreactors designed to remove selenite from water.