Assessment of genetic diversity among African cassava Manihot esculenta Grantz accessions resistant to the cassava mosaic virus disease using SSR markers   总被引：1，自引：0，他引：1  

Yvonne Lokko  Alfred Dixon  Sam Offei  Eric Danquah  Martin Fregene 《Genetic Resources and Crop Evolution》2006,53(7):1441-1453

A study was conducted to determine the extent of genetic diversity among African cassava (Manihot esculenta Crantz) accessions resistant to the cassava mosaic virus disease (CMD), using simple sequence repeat (SSR) markers. The accessions included a breeding stock (clone 58308), five improved lines, 62 CMD resistant and 10 CMD susceptible landraces. Genetic diversity was assessed among accessions in five cluster groups derived from UPGMA analysis on data from 18 SSR primer pairs. Average gene diversity, He, was high in all cluster groups, with an average heterozygosity of 0.591 ± 0.061. The estimator of inbreeding Fis revealed a low level of inbreeding within groups and averaged −0.262 ± 0.142. Gene diversity among all accessions was 51.4% and gene diversity within cluster groups was 46.6%, while 4.8% was due to diversity between the different cluster groups. The amount of genetic differentiation measured by Gst and Fst were 9.6% and 12.1% respectively, indicating a weak genetic structure.  相似文献   

Über einige Spirogyren aus dem Harz     

Alfred Rieth 《Genetic Resources and Crop Evolution》1987,35(2):453-479

Zusammenfassung In Algenaufsammlungen aus dem Harzgebiet wurden achtSpirogyra-Arten gefunden, an Freiland- sowie Kulturmaterial untersucht und dabei die Variationsbreite einiger Merkmale durch umfangreiche Messungen geprüft.

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On someSpirogyra species of the Harz mountains

Summary Eight species ofSpirogyra found in collections of algae from the Harz mountains were studied on living material from the natural site and on cultures derived from it. Based on numerous measurements, the variability of some characteristics is investigated.

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8 Spirogyra. ; .

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Charge transfer equilibria between diamond and an aqueous oxygen electrochemical redox couple     

Chakrapani V  Angus JC  Anderson AB  Wolter SD  Stoner BR  Sumanasekera GU 《Science (New York, N.Y.)》2007,318(5855):1424-1430

Undoped, high-quality diamond is, under almost all circumstances, one of the best insulators known. However, diamond covered with chemically bound hydrogen shows a pronounced conductivity when exposed to air. This conductivity arises from positive-charge carriers (holes) and is confined to a narrow near-surface region. Although several explanations have been proposed, none has received wide acceptance, and the mechanism remains controversial. Here, we report the interactions of hydrogen-terminated, macroscopic diamonds and diamond powders with aqueous solutions of controlled pH and oxygen concentration. We show that electrons transfer between the diamond and an electrochemical reduction/oxidation couple involving oxygen. This charge transfer is responsible for the surface conductivity and also influences contact angles and zeta potentials. The effect is not confined to diamond and may play a previously unrecognized role in other disparate systems.  相似文献   

Software and the future of programming languages     

Aho AV 《Science (New York, N.Y.)》2004,303(5662):1331-1333

Although software is the key enabler of the global information infrastructure, the amount and extent of software in use in the world today are not widely understood, nor are the programming languages and paradigms that have been used to create the software. The vast size of the embedded base of existing software and the increasing costs of software maintenance, poor security, and limited functionality are posing significant challenges for the software R&D community.  相似文献   

HIV testing for whole populations     

Prince AM 《Science (New York, N.Y.)》2008,321(5896):1631-4; author reply 1631-4

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Planetary science. Active volcanism on Io     

McEwen AS 《Science (New York, N.Y.)》2002,297(5590):2220-2221

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Saving the small farm: Agriculture in roman literature     

Alfred Wolf 《Agriculture and Human Values》1987,4(2-3):65-75

Roman agriculture suffered traumatic changes during the 2nd century B.C. The traditional farmers who tilled their few acres and served family, gods and community were being squeezed out by large estate owners using slaves for investment farming. Politicians, scholars and poets tried to revive the ancestoral rustic life. In 133 B.C. the Gracchi legislated land reform to relieve the distress of the farmer soldiers who had won the empire. Although their efforts led to political confrontation that deteriorated into civil war, programs for the traditional farm became a permanent part of government policy from the late Republic until the end of the empire in 476 A.D. Scholars and poets made a contribution to the revival of agriculture with knowledge for improving the farm and by encouraging an agrarian mentality. The agricultural manuals (e.g. Cato (c. 150 B.C.), Varro (c. 50 B.C), and Columella (c.65 A.D.), defined the nature of the desirable farm and gave practical advice. Profit was the goal, but good farming practices made for pleasure and virtue as well. The image of the ancestoral farmer was perpetuated as was the notion that farming was the only honorable and respectable occupation for a Roman gentleman. In the Augustan Age (34 B.C.—14 A.D.) poets were encouraged by the government to adopted a rustic theme in hopes it would stimulate a return to the land and aid in the rebirth of Rome and Romans. In the GeorgicsVirgil begins with the practical details of farming, but uses myth and philosophy to explore the nature and meaning of life. He admits that Jove made life perilous. But Jove also gave man the art of agriculture and with hard work man could know the pleasure of a simple, virtuous, productive life. Horace directed his poetry against the allure of city life and in praise of rustic living. Epicureanism and Stoicism, in the guise of life on the farm, could show that although fate was unpredictable, the world was orderly and, if one recognized and accepted its limits, one could make a garden of the world and live a simple but happy life. By 300 A.D. Rome missed the peasant-farmer-soldier and by the 470's life had returned to an agrarian condition. Bishop Sidonius, trying to furnish meaning and perspective for the emerging new age, resorted to the Roman agricultural traditions still cherished as that world disappeared.  相似文献   

Bypass of DNA lesions generated during anticancer treatment with cisplatin by DNA polymerase eta     

Alt A  Lammens K  Chiocchini C  Lammens A  Pieck JC  Kuch D  Hopfner KP  Carell T 《Science (New York, N.Y.)》2007,318(5852):967-970

DNA polymerase eta (Pol eta) is a eukaryotic lesion bypass polymerase that helps organisms to survive exposure to ultraviolet (UV) radiation, and tumor cells to gain resistance against cisplatin-based chemotherapy. It allows cells to replicate across cross-link lesions such as 1,2-d(GpG) cisplatin adducts (Pt-GG) and UV-induced cis-syn thymine dimers. We present structural and biochemical analysis of how Pol eta copies Pt-GG-containing DNA. The damaged DNA is bound in an open DNA binding rim. Nucleotidyl transfer requires the DNA to rotate into an active conformation, driven by hydrogen bonding of the templating base to the dNTP. For the 3'dG of the Pt-GG, this step is accomplished by a Watson-Crick base pair to dCTP and is biochemically efficient and accurate. In contrast, bypass of the 5'dG of the Pt-GG is less efficient and promiscuous for dCTP and dATP as a result of the presence of the rigid Pt cross-link. Our analysis reveals the set of structural features that enable Pol eta to replicate across strongly distorting DNA lesions.  相似文献   

The metal — Metal interactions in biological systems Part III. Daphnia magna     

Piotr Tomasik  Christopher H. D. Magadza  Sungano Mhizha  Alfred Chirume 《Water, air, and soil pollution》1995,82(3-4):695-711

The toxicity of single metal ions: Al, Co(II), Cr(III), Cu(II), Fe(III), Mg, Mn(II), Mo(VI), Ni(II), Se(VI), V(V) and Zn and the following pairs of them: Al-Co, Al-Mg, Al-Mo, Al-Se, Al-Zn, Cr-Co, Cr-Mg, Cr-Mo, Cr-Se, Cr-Zn, Cu-Co, Cu-Mg, Cu-Mo, Cu-Se, Cu-Zn, Fe-Co, Fe-Mg, Fe-Mo, Fe-Se, Fe-Zn, Mn-Co, Mn-Mg, Mn-Mo, Mn-Se, Mn-Zn, Ni-Co, Ni-Mg, Ni-Mo, Ni-Se, Ni-Zn, V-Co, V-Mg, V-Mo, V-Se, V-Zn, Zn-Co, Zn-Mg, Zn-Mo, and Zn-Se on Daphnia magna was examined. The most prominent antagonism in the toxicity was observed in the following ion pairs: Al-Mo(VI), Cr(III)-Co(II), Cr(III)-Mg, Cr(III)-Mo(VI), Cr(III)-Se(VI), Cr(III)-Zn, Fe(III)-Se(VI), Mn(II)-Mg, Mn(II-Se(VI), Zn-Mg and Zn-Mo(VI). The strong synergism was found for the following ion systems: Cr(III)-Se(VI), Cr(III)-Zn, Fe(III)-Se(VI), Mn(II)-Zn, Mn(II)-Se(VI), Ni(II)-Co(II), Ni(II)-Mo(VI), Ni(II)-Se(VI), Ni(II)-Zn, V(V)-Co(II), V(V)-Mo(VI), V(V)- Se(VI), and V(V)-Zn. Synergism and antagonism in toxicity were dependent on water hardness as well as on the ion concentration. Adaptive procesess of the animals to the toxic environment could also be observed. Thus, the toxicity of the single ions and their pairs was not linear with respect to time.  相似文献   

    

Alfred Rieth 《Genetic Resources and Crop Evolution》1984,32(4):261-272

Zusammenfassung Es wird eineVaucheria aus dem Hochharz nach Freilandfunden 1981 und 1982, sowie an Hand von Kulturen beschrieben, die in ihren Merkmalen eine gewisse Mittelstellung zwischenV. pseudogeminata Dangeard undV. alaskana Blum einnimmt. Die zahlreich beobachteten Prolifikationen im Sexualorganbereich werden analysiert.Summary AVaucheria-species is described from the Harz Mountains which, within thepseudogeminata group holds a position betweenV. pseudogeminata andV. alaskana. Parallel cultivation ofV. pseudogeminata and the Harz-Vaucheria under identical conditions revealed, that there exist clear cut differences between these two. A discrimination toV. alaskana, for reasons discussed in the paper, is not so easy. So, for the time being—with all reservations—the Harz material is assigned to this species, but supposed, that it may be a different, new species.

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Vaucheriaceae. XXIV. , pseudogeminata

Vaucherica 1981 1982 ., , V. pseudogeminata Dangeard V. alaskana Blum .

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