Tunable differential conductance of single wall C/BN nanotube heterostructure

The transport properties and differential conductance of the heterostructures constructed by (5,5) single wall carbon nanotube (SWCNT) and (5,5) single wall boron nitride nanotube (SWBNNT) are investigated using density functional theory in combination with non-equilibrium Green’s functions. We find that the transmission conductance of (5,5) BN/C nanotube heterostructure is not only continually depressed as the BNNT region increases but also the drop of the conductance is uniform in the energy window (?1.43 eV, 1 eV), which leads to linear I–V dependence for the systems when the bias is within this energy range. Moreover, the differential conductance linearly decreases when n?≤?3 but exponentially decreases when n?≥?3 for (5,5)(BN) _n /C heterostructure. Such tunable differential conductance of (5,5) BN/C nanotube heterostructure mainly derives from the blockage of the transport channels induced by the semiconductive BN segment.

Synthesis,antimicrobial activity and acid dissociation constants of methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives

In this study, a series of polysubstituted methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives were designed and synthesized by the cyclization reaction of methyl 1-(benzoylcarbamothioyl)-5,5-diphenylpyrrolidine-2-carboxylates and 2-bromo-1-(4-substituted phenyl)ethanones in 70–96% yield. The starting pyrrolidine derivatives were synthesized via a 1,3-dipolar cycloaddition reaction in 83–88% yield. The stereochemistry of one of these methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives was characterized by a single crystal X-ray diffraction study and the acid dissociation constants of these compounds were determined. An antimicrobial screening was performed against different bacterial and fungal strains and against the M. tuberculosis H37Rv strain. Interesting antibacterial activity was observed for two compounds against the A. baumannii strain with MIC values of 31.25?µg/mL (Ampicillin: 125?µg/mL) and against the M. tuberculosis H37Rv strain with MIC values of 0.98–1.96?µg/mL (Isoniazid: 0.98?µg/mL, Ethambutol: 1.96?µg/mL). Therefore, these structures can be considered as good starting points for the development of new powerful antimycobacterial agents.     

Calcium complexation with a highly calcium selective chelator: crystal structure of ca(CaFBAPTA) ·5H2O

The structure of the complex of calcium ions with 5,5'-difluoro-1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (FBAPTA) has been determined. The calcium complex, with stoichiometry Ca(CaFBAPTA) · 5H₂O crystallizes in a monoclinic space group P2₁/c with 4 formula units/unit cell with a(Å) = 9.767, b(Å) = 26.309,c(Å) = 11.769; β (deg) = 111.57. The structure may be considered as the calcium salt of a CaFBAPTA2- complex in which the octacoordinate calcium ion is complexed with the two ether oxygen atoms, the two nitrogens, and coordinated in a unidentate manner with the four acetate carboxyl groups. The geometry of the nitrogen atoms is nearly tetrahedral and provides a basis for the interpretation of the optical perturbations which result from calcium complexation with BAPTA type ligands. In addition, it is clear from the distance and relative orientation of the aromatic rings that ring current contributions to the fluorine chemical shifts are of negligible importance, so that such effects cannot be used in the design of NMR active indictators. Although BAPTA and analogs such as PBAPTA and quin2 have found extensive physiological applications as a consequence of the high degree of selectivity for calcium ions over magnesium ions which they exhibit, this is the first reported structural data for any of these complexes.     

Regulation of biosynthesis of secondary metabolites

Partially purified citrate synthase (EC 4.1.3.7) was isolated from submerged mycelium ofStreptomyces aureofaciens RIA 57, a strain producing chlortetracycline. Enzymatic activity was determined spectrophotometrically by means of 5,5′-dithio-bis-(2-nitrobenzoic acid). Citrate synthase was inhibited by ATP, inhibition being competitive with respect to acetyl coenzyme A. In 5mm concentration, ATP caused 55% inhibition of the enzyme. ADP, in the same concentration, caused 30% inhibition, while AMP caused none. Other natural nucleoside di- and triphosphates, in 1–5mm concentration, did not significantly affect citrate synthase inStreptomyces aureofaciens. Mg²⁺ inhibited the activity of the enzyme, but also reduced the negative effect of ATP. The role of ATP in regulation of the metabolic paths of acetyl CoA is discussed.     

The gut anaerobe Faecalibacterium prausnitzii uses an extracellular electron shuttle to grow at oxic–anoxic interphases

Faecalibacterium prausnitzii is one of the most abundant bacteria in the human gut ecosystem and it is an important supplier of butyrate to the colonic epithelium. Low numbers of faecalibacteria have been associated with inflammatory bowel disease. Despite being extremely oxygen sensitive, F. prausnitzii is found adherent to the gut mucosa where oxygen diffuses from epithelial cells. This paradox is now explained on the basis of gas tube experiments, flavin-dependent reduction of 5,5′-dithiobis-2-nitrobenzoate and microbial fuel cell experiments. The results show that F. prausnitzii employs an extracellular electron shuttle of flavins and thiols to transfer electrons to oxygen. Both compounds are present in the healthy human gut. Our observations may have important implications for the treatment of patients with Crohn''s disease, for example, with flavin- or antioxidant rich diets, and they provide a novel key insight in host–microbe interactions at the gut barrier.     

Synthesis and Anti-Tubercular (Tb) Evaluation of Bis[4-Ethylidineamino[1,2,4]Triazole-3-Thiol] Tethered by 1,4-Dihydropyridine

Russian Journal of Bioorganic Chemistry - A new series of 5,5'-(2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3,5-diyl)bis[4-(ethylideneamino)-4H-[1,2,4]-triazole-3-thiol) was synthesized via...     

Metabolism of l-β-lysine by a Pseudomonas: Purification and properties of 3-keto-6-acetamidohexanoate cleavage enzyme

Extracts of Pseudomonas B4 grown with l-β-lysine (3,6-diaminohexanoate) as the main energy source are shown to contain a 3-keto-6-acetamidohexanoate cleavage enzyme that converts 3-keto-6-acetamidohexanoate and acetyl · CoA reversibly to 4-acetamidobutyryl · CoA and acetoacetate. The enzyme catalyzes the third step in β-lysine degradation. In unfractionated extracts cleavage enzyme activity is generally assayed spectrophotometrically by coupling the forward reaction with excess 4-acetamidobutyryl · CoA thiolesterase, derived from the same organism, and measuring the rate of CoASH formation by reaction with 5,5-dithiobis(2-nitrobenzoic acid). Enzyme freed of thiolesterase is conveniently assayed by using 4-acetamidobutyryl · CoA and acetoacetate as substrates and measuring acetyl · CoA formation by means of citrate synthase reaction in the presence of 5,5-dithiobis(2-nitrobenzoic acid). The cleavage enzyme has been purified 38-fold to a specific activity of 237 mU/mg. The stoichiometry, equilibrium constant, molecular weight, and various kinetic properties of the enzymatic reaction have been determined. The substrate specificity of the Pseudomonas enzyme differs markedly from that of the analogous 3-keto-5-aminohexanoate cleavage enzyme of Clostridium subterminale strain SB4 and is broader. In the forward reaction 3-ketohexanoate can replace 3-keto-6-acetamidohexanoate, and propionyl · CoA can replace acetyl · CoA as a substrate. In the backward reaction, 4-acetamidobutyryl · CoA can be replaced by any of several CoA thiolesters including the butyryl, valeryl, 4-propionamidobutyryl, 3-acetamidopropionyl, and β-alanyl derivatives, and acetoacetate can be replaced by 2-methylacetoacetate. The products of these reactions have been characterized. Unlike the cleavage enzyme of Clostridium subterminale strain SB4, the Pseudomonas enzyme is not stimulated by Co²⁺ or Mn²⁺ and is not inhibited by EDTA, 5,5-dithiobis(2-nitrobenzoic acid), or p-chloromercuribenzoate. Tracer experiments indicate that carbon atoms 1 and 2 of acetoacetate are derived from carbon atoms 1 and 2 of 3-keto-6-acetamidohexanoate, and carbon atoms 3 and 4 of acetoacetate are derived from the acetyl group of acetyl · CoA. The cleavage enzyme is not formed in detectable amounts when Pseudomonas B4 is grown in a peptone-yeast extract medium.     

Interrelationship of Meloidogyne hapla and Ditylenchus dipsaci on Resistant and Susceptible Alfalfa

Simultaneous inoculations of alfalfa with Meloidogyne hapla larvae and Ditylenchus dipsaci at 16, 20, 24, and 28 C did not depress penetration of either nematode in ''Nev Syn XX'' -a selection resistant to M. hapla and D. dipsaci, ''Vernal 298'' -a selection resistant to M. hapla and susceptible to D. dipsaci, ''Lahontan'' -a cultivar resistant to D. dipsaci and susceptible to M. hapla, and ''Ranger'' -a cultivar susceptible to both M. hapla and D, dipsaci. Infection with D. dipsaci depressed growth of susceptible ''Vernal 298'' and ''Ranger'' at all soil temperatures, except for ''Vernal 298'' at 16 C. Infection with M. hapla alone did not depress growth of any of the alfalfas. A combination of M. hapla and D. dipsaci resulted in a synergistic weight depression on ''Ranger'' at all soil temperatures. Inoculation of the four alfalfas with D. dipsaci 2, 4, 6, and 8 wk before inoculation with M. hapla at 16, 20, 24, and 28 C did not influence the resistance or susceptibility of ''Nev Syn XX,'' ''Lahontan,'' or ''Ranger.'' However, galling of ''Vernal 298'' by M. hapla was affected by soil temperature, plant age, and inoculation with D. dipsaci.     

Optical stability of gossypol

The optical stability of gossypol [1,1',6,6',7,7'-hexahydroxy-3,3'-dimetyl-5,5'-bis(1-methylethyl)-2,2'-binaphthalene-8,8'-dicarboxaldehyde], a natural product exhibiting profoundly enantiospecific antitumor and male antifertility action, was investigated by means of computational methods and thermal racemization experiments. The calculations on gossypol and several derivatives and model compounds were carried out using the MM2 force field; energies and geometries of minimum energy conformations, as well as structures along various inversion pathways, were calculated. According to the calculations, gossypol (the dialdehyde form) and its simple analogues are not thermally racemizable (energy barriers for rotational inversion above 50 kcal/mol). By contrast, the calculations suggest that the acetal tautomer of gossypol and its dehydration product (anhydrogossypol) are thermally racemizable, although the energy barriers are still relatively high (35–40 kcal/mol). Optically pure (+)-anhydrogossypol was prepared and characterized; its racemization became rapid only at high temperatures (180–200°C). When dehydration of gossypol was hindered (in aqueous solution), no racemization of gossypol was observed after prolonged heating at 90°C. © 1992 Wiley-Liss, Inc.     

Peanut Pod Invasion by Aspergillus flavus in the Presence of Meloidogyne hapla

''Argentine'', ''Early Runner'' and ''Florigiant'' peanut cultivars were grown in methyl bromide treated soil in field microplots inoculated with: (i) Aspergillus flavus or (ii) A. flavus + Meloidogyne hapla. Nematode infection produced heavy root galling and light pod galling equally on all cultivars. A. flavus, A. niger, Cephalosporium spp., Colletotrichum sp., Curvularia spp., Fusarium spp., Penicillium spp. and Trichoderma viride were isolated from shells and kernels. A significantly greater incidence and density of A. flavus was obtained from kernels of plants inoculated with both organisms than from kernels of plants receiving only the fungus. Differences were not significant, however, for incidence and density of A. flavus in shells or for the total of all fungal propagules in shells and kernels. Shells of ''Early Runner'' contained significantly greater incidence and density of A. flavus than the other two cultivars; also, kernels of this cultivar contained more fungal propagules than kernels of ''Argentine.'' A significantly larger number of total fungi was isolated from kernels of ''Argentine'' than from ''Florigiant.'' Aflatoxins were found only in two shell samples and not in kernels.     

Host Suitability of Selected Hybrids,Varieties and Inbreds of Corn to Populations of Meloidogyne spp.

Rates of reproduction of root-knot nematodes on corn varied with Meloidogyne species, with different populations of certain species, and with corn cultivars. M. arenaria, M. incognita and M. javanica reproduced at varying rates on all corn cultivars tested. None of the three selections of M. hapla reproduced on corn. Most of the Meloidogyne populations increased more rapidly on ''Coker'' and ''Pioneer'' hybrids than on ''McNair'' hybrids or on open-pollinated varieties or inbreds. Nematodes often reduced root growth, but the differences within given nematode-cultivar treatments were not usually significant. Root growth of ''Coker 911,'' which supported a high rate of reproduction, was affected less than ''Pioneer 309B'' which supported a low rate of nematode reproduction.     

Comparison of Ellman's reagent with N-(1-pyrenyl)maleimide for the determination of free sulfhydryl groups in reduced cellobiohydrolase I from Trichoderma reesei

The enzyme cellobiohydrolase I (CBH I) from Trichoderma reesei was treated with 5 mM dithiothreitol at different pH values in order to reduce some or all of its 12 disulfide bridges. A discrepancy was found in the number of free sulfhydryl (SH) groups generated upon the reduction of CBH I when they were measured using N-(1-pyrenyl)maleimide (PM) or Ellman's reagent, 5,5′-dithiobis(2-nitrobenzoic acid). For example, the number of SH mol generated/mol CHB I at pH 8.5 was determined to be 16 and < 1 when measured using PM or Ellman's reagent, respectively. The low value obtained with Ellman's reagent may be due to the electrostatic repulsion between the carboxylic acid groups in CBH I and those in Ellman's reagent. The fluorimetric assay used for determining SH molecules in reduced CBH I, based on their reaction with PM, is described.     

Pathogenicity and Interaction of Three Nematode Species on Six Bermudagrasses

The ring nematode (Criconemoides ornatus), stunt nematode (Tylenchorhynchus martini), and sting nematode (Belonolaimus Iongicaudatus) reproduced readily on six bermudagrasses (Common, ''U-3'', ''Tufcote'', ''Continental'', ''Tiffine'', and ''Tifdwarf''). Populations of a single nematode species influenced the population development of a second and third parasitic nematode species on a particular host plant. Activity of most nematodes adversely affected reproduction of other nematode species in mixed cultures. Generally, the number of fibrous roots produced by plants decreased as the number of nematode species in the treatments increased. Tifdwarf bermudagrass appeared to be more tolerant to C. ornatus and T. martini than other grasses tested.     

Parasitism of Hoplolaimus galeatus on Diploid and Polyploid St. Augustine grasses

''Floratam'' and ''FX-313'' St. Augusfinegrasses (Stenotaphrum secundatum) were compared in a time-course experiment for host suitability and susceptibility to the lance nematode, Hoplolaimus galeatus. Nematode densities were determined in the soil and acid-fuchsin stained roots 42, 84, 126, 168, and 210 days after pots containing 230 cm³ of autoclaved native Margate fine sand/pot were infested with 104 ± 9 nematodes and maintained at 25 ± 2 C in the laboratory. ''FX-313'' was a more suitable host for H. galeatus. Numbers of H. galeatus reached a maximum at 210 days after inoculation, with 5,550 and 4,120 nematodes (adults plus juveniles)/pot for ''FX-313'' and ''Floratam,'' respectively. Root and shoot dry weights of both grasses were not affected by H. galeatus throughout the experiment. Three polyploid, 2n = 30 to 32 (''Floratam,'' ''FX-10,'' and ''Bitterblue'') and three diploid, 2n = 18 (''FX-313,'' ''Florida Common,'' and ''Seville'') S. secundatum genotypes were inoculated with H. galeatus (99 ± 9/pot) and compared with uninoculated controls 210 days after inoculation. St. Augustinegrass genotypes differed as hosts of H. galeatus. ''FX-313'' and ''Florida Common'' represented the high and low extremes, respectively, for nematode reproduction (9,750 and 5,490 nematodes/pot or 4,239 and 2,387 nematodes/100 cm³ of soil). However, differences in root and shoot growth were not detected 210 days after inoculation with H. galeatus.     

A revision of the genus Planinasus Cresson (Diptera,?Periscelididae)

The genus Planinasus Cresson is revised and includes 18 extant and one fossil species. We clarify the status of the three previously described species and describe 15 new species as follows (type locality in parenthesis): Planinasus aenigmaticus (Colombia. Bogota: Bogota (04°35.8''N, 74°08.8''W)), Planinasus neotropicus (Panama. Canal Zone: Barro Colorado Island (09°09.1''N, 79°50.8''W)), Planinasus kotrbae (Ecuador. Orellana: Rio Tiputini Biodiversity Station (0°38.2''S, 76°08.9''W)), Planinasus miradorus (Brazil. Maranhão: Parque Estadual Mirador, Base da Geraldina (06°22.2''S, 44°21.8''W)), Planinasus tobagoensis (Trinidad and Tobago. Tobago. St. John: Parlatuvier (11°17.9''N, 60°39''W)), Planinasus xanthops (Ecuador. Orellana: Rio Tiputini Biodiversity Station (0°38.2''S, 76°8.9''W)), Planinasus argentifacies (Peru. Madre de Dios: Río Manu, Pakitza (11°56.6''S, 71°16.9''W; 250 m)), Planinasus insulanus (Dominican Republic. La Vega: near Jarabacoa, Salto Guasara (19°04.4''N, 70°42.1''W, 680 m)), Planinasus nigritarsus (Guyana. Conservation of Ecological Interactions and Biotic Associations (CEIBA; ca. 40 km S Georgetown; 06°29.9''N, 58°13.1''W)), Planinasus atriclypeus (Brazil. Rio de Janeiro: Rio de Janeiro, Floresta da Tijuca (22°57.6''S, 43°16.4''W)), Planinasus atrifrons (Bolivia. Santa Cruz: Ichilo, Buena Vista (4-6 km SSE; Hotel Flora y Fauna; 17°29.95''S, 63°33.15''W; 4-500 m)), P. flavicoxalis (West Indies. Dominica. St. David: 1.6 km N of junction of roads to Rosalie and Castle Bruce (15°23.8''N, 61°18.6''W)), Planinasus mcalpineorum (Mexico. Chiapas: Cacahoatan (7 km N; 15°04.1''N, 92°07.4''W)), Planinasus nigrifacies (Brazil. São Paulo: Mogi das Cruzes, Serra do Itapeti (23°31.5''S, 46°11.2''W)), Planinasus obscuripennis (Peru. Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7''S, 71°23.3''W; 550 m)). In addition to external characters, we also describe and illustrate structures of the male terminalia and for Planinasus kotrbae sp. n., the internal female reproductive organs. Detailed locality data and distribution maps for all species are provided. For perspective and to facilitate genus-group and species-group recognition, the family Periscelididae and subfamily Stenomicrinae are diagnosed and for the latter, a key to included genera is provided.     

Pathogenicity of Four Species of Meloidogyne on Three Varieties of Olive Trees

''Ascolano'' and ''Sevillano'' olive trees, Olea europaea L., were highly susceptible to Meloidogyne javanica (Trueb) Chitwood, and growth of their tops was decreased greatly in tests in a glasshouse. Roots of ''Manzanillo'' olive trees were galled moderately by M. javanica, and their tops weighed 6% less than those of noninoculated trees. ''Manzanillo'' olive is considered highly tolerant to M. javanica. ''Ascolano'' and ''Manzanillo'' olive trees were highly susceptible to M. incognita (Kofoid &White) Chitwood. Their roots were galled moderately to severely, and growth of their tops were decreased between 13% and 44%. ''Ascolano'' and ''Manzanillo'' olive trees were considered to be highly resistant to M. arenaria (Neal) Chitwood and M. hapla Chitwood since no galls or mature females were found on their roots three and one-half months after inoculation.     

A revision of the new world species of Polytrichophora Cresson and Facitrichophora,new genus (Diptera,?Ephydridae)

The New World species of Polytrichophora Cresson and Facitrichophora new genus, are revised. Fifteen new species are described (type locality in parenthesis): Facitrichophora atrella sp. n. (Costa Rica. Guanacaste: Murciélago [10°56.9''N, 85°42.5''W; sandy mud flats around mangrove inlet]), Facitrichophora carvalhorum sp. n. (Brazil. São Paulo: Praia Puruba [23°21''S, 44°55.6''W; beach]), Facitrichophora manza sp. n. (Trinidad and Tobago. Trinidad. St. Andrew: Lower Manzanilla (12 km S; 10°24.5''N, 61°01.5''W), bridge over Nariva River), Facitrichophora panama sp. n. (Panama. Darien: Garachine [8°04''N, 78°22''W]), Polytrichophora adarca sp. n. (Barbados. Christ Church: Graeme Hall Nature Sanctuary [13°04.2''N, 59°34.7''W; swamp]), Polytrichophora arnaudorum sp. n. (Mexico. Baja California. San Felipe [31°01.5''N, 114°50.4''W]), Polytrichophora barba sp. n. (Cuba. Sancti Spiritus: Topes de Collantes [21°54.4''N, 80°01.4''W, 670 m]), Polytrichophora flavella sp. n. (Peru. Madre de Dios: Rio Manu, Pakitza [11°56.6''S, 71°16.9''W; 250 m]), Polytrichophora marinoniorum sp. n. (Brazil. Paraná: Antonina [25°28.4''S, 48°40.9''W; mangal]), Polytrichophora rostra sp. n. (Peru. Madre de Dios: Rio Manu, Pakitza [11°56.6''S, 71°16.9''W; 250 m]), Polytrichophora sinuosa sp. n. (Trinidad and Tobago. Trinidad. St. Andrew: Lower Manzanilla [12 km S; 10°24''N, 61°02''W]), Polytrichophora mimbres sp. n. (United States. New Mexico. Grant: Mimbres River [New Mexico Highway 61 & Royal John Mine Road; 32°43.8''N, 107°52''W; 1665 m]), Polytrichophora salix sp. n. (United States. Alaska. Matanuska-Susitna: Willow Creek [61°46.1''N, 150°04.2''W; 50 m]), Polytrichophora sturtevantorum sp. n. (United States. Tennessee. Shelby: Meeman Shelby State Park [Mississippi River; 35°20.4''N, 90°2.1''W; 98 m]), Polytrichophora prolata sp. n. (Belize. Stann Creek: Cockscomb Basin Wildlife Sanctuary [16°45''N, 88°30''W]). All known New World species of both genera are described with an emphasis on structures of the male terminalia, which are fully illustrated. Detailed locality data and distribution maps for all species are provided. For perspective and to facilitate recognition, the tribe Discocerinini is diagnosed and a key to included genera is provided.     

Resistance of Some Vitis Rootstocks to Xiphinema index

Thirty-eight grapevine (Vitis spp.) rootstocks were screened in pots for resistance to the dagger nematode, Xiphinema index, from 1979 to 1981. Resistance ratings were based on visible root symptoms and on changes in the nematode populations over 16 months. Nineteen of the 23 Californian hybrid rootstocks tested were resistant, as were ''Harmony'','' ''Freedom,'' ''Schwarzmann,'' and ''3309.'' Two hybrids of V. rufotomentosa, ''171-52'' and ''176-9,'' were possibly immune to X. index. The rootstocks ''ARG 1,'' '' 110 R,'' ''1202,'' and ''1616,'' which are used commercially for phylloxera resistance were susceptible.     

A revision of the shore-fly genus Hydrochasma Hendel (Diptera,Ephydridae)

A revision of the shore-fly genus Hydrochasma Hendel. The species of the genus Hydrochasma Hendel are revised, including 27 new species (type locality in parenthesis): H. andeum (Ecuador. Guayas: Boliche (02°07.7''S, 79°35.5''W)), H. annae (United States. Utah. Grand: Swasey Beach (15.3 km N Green River; 39°07''N, 110°06.6''W; Green River; 1255 m)), H. capsum (Ecuador. Orellana: RíoTiputini (0°38.2''S, 76°8.9''W)), H. castilloi (Ecuador. Loja: Catamayo (03°59''S, 79°21''W)), H. crenulum (Peru. Cuzco: Paucartambo, Atalaya (Río Alto Madre de Dios; 12°53.3''S, 71°21.6''W; 600 m)), H. denticum (Ecuador. Orellana: Río Tiputini (0°38.2''S, 76°8.9''W)), H. digitatum (Peru. Madre de Dios: Diamante (Río Alto Madre de Dios; 12°19.9''S, 70°57.5''W; 400 m)), H. distinctum (Costa Rica. Limón: Parque Nacional Barbilla, Sector Casas Negras, (10°0.8''N, 83°28.1''W; 300 m)), H. dolabrutum (Dominican Republic. Barahona: Barahona (18°12''N, 71°5.3''W)), H. edmistoni (Dominican Republic. Azua: near Pueblo Viejo (18°24.8''N, 70°44.7''W)), H. falcatum (Peru. Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7''S, 71°23.3''W; 550 m)), H. glochium (Dominican Republic. Peravia: San José Ocoa (10 km NE; 18°35''N, 70°25.6''W)), H. kaieteur (Guyana. Kaieteur Falls (05°10.5''N, 59°26.9''W)), H. lineatum (Trinidad and Tobago. Trinidad. St. George: Filette (1 km SE; 10°47''N, 61°21''W)), H. miguelito (Honduras. Cortés: San Pedro Sula (8 km S; 15°25.7''N, 88°01.4''W)), H. octogonum (Ecuador. Manabí: Pichincha (01°02.7''S, 79°49.2''W)), H. parallelum (Trinidad and Tobago. Trinidad. St. Andrew: Lower Manzanilla (16 km S; 10°22''N, 61°01''W)), H. peniculum (Dominican Republic. Pedernales: Pedernales (18°01.8''N, 71°44.7''W)), H. rictum (Honduras. Cortés: San Pedro Sula (8 km S; 15°25.7''N, 88°01.4''W)), H. robustum (Brazil. São Paulo. Ubatuba, Praia Puruba (23°21''S, 44°55.6''W; beach)), H. sagittarium (Trinidad and Tobago. Tobago: St. John: Parlatuvier (creek; 11°17.9''N, 60°35''W)), H. simplicum (Costa Rica. Limón: Parque Nacional Barbilla, Sector Casas Negras, (10°01.2''N, 83°26.2''W; 300 m)), H. sinuatum (Belize. Stann Creek: Mullins Creek (17 km N Dangriga; 17°06.2''N, 88°17.8''W)), H. spinosum (Costa Rica. Limón: Westfalia (4 km S; 09°54.5''N, 82°59''W; beach)), H. urnulum (Dominican Republic. Puerto Plata: Río Camu (14 km E Puerto Plata; 19°41.9''N, 70°37.5''W)), H. viridum (Guyana. Karanambo, Rupununi River (ox bow; 03°45.1''N, 59°18.6''W)), H. williamsae (Belize. Stann Creek: Mullins River (17 km N Dangriga; 17°06.2''N, 88°17.8''W)). All known species are described with an emphasis on structures of the male terminalia, which are fully illustrated. Detailed locality data and distribution maps for all species are provided. A lectotype is designated for Discocerina incisum Coquillett and Hydrochasma zernyi Hendel. For perspective and to facilitate genus-group and species-group recognition, the tribe Discocerinini is diagnosed and a key to included genera in the New World is provided.     

Comparison of Five Populations of Tylenchulus semipenetrans to Citrus,Poncirus, and their Hybrids

The infectivity of five populations of Tylenchulus semipenetrans were compared and differentiated on 10 hosts (5 Citrus spp., 1 Poncirus trifoliata, and 4 hybrids of Citrus spp. X P. trifoliata). Differences in levels of infection and development (P = 0.01) occurred between Citrus spp. and P. trifoliata cv. ''Pomeroy'' and their three hybrids, C. paradisi X P. trifoliata cv. ''Swingle'' citruntelo and C. sinensis, cv. ''Ruby'' orange X P. trifoliata cv. ''Webber Fawcett 14-7'', and ''15-7''. Poncirus trifoliata cv. Pomeroy was susceptible to a California biotype 3 and highly resistant to the other citrus nematode populations. Low infection levels with California biotype 1, Arizona, and Florida populations on Swingle citrumelo, and the two Ruby orange hybrids indicated inherited resistance. Reproduction of the nematode population from Texas was greatest on the three hybrids, Swingle citrumelo, Ruby orange 14-7, and 15-7, from the California 1, Arizona, and Florida populations, but its comparable densities on P. trifoliata and Citrus spp. were not sufficiently different from these populations to consider it a separate biotype. California biotype 3 was sufficiently different from all other populations to be considered a different biotype, and it was named the "Poncirus biotype."