Proline production via the arginine biosynthetic pathway: transfer of regulatory mutations of arginine biosynthesis into a proline-producing strain ofSerratia marcescens

Summary Proline production via a part of the arginine biosynthetic pathway was examined. About 20 mg/ml ofl-proline was produced by using arginine biosynthetic enzymes. Accordingly, three mutations of arginine biosynthesis, namely, derepression of arginine biosynthetic enzymes (assigned byargR2), feedback inhibition-resistant N-acetylglutamate synthase (assigned byargA2) and defectiveness in N-acetylornithine aminotransferase (assigned byargD ^–) were introduced by three transductional crosses into a proline-producing strain which produced about 55 mg/ml ofl-proline. The constructed strain produced 62 mg/ml ofl-proline, although about 10 mg/ml ofl-arginine and 1 mg/ml of N-acetylglutamate--semialdehyde were produced as by-products.     

Hybridisation,genomic constitution and generic delimitation inElymus s. l. (Poaceae: Triticeae)

Intergeneric crosses were made between representatives of the genomically-defined generaElymus, Agropyron, Elytrigia, Pseudoroegneria, andThinopyrum. The genomic constitution ofElytrigia repens, the type species ofElytrigia, is shown to be SSH, a genomic combination otherwise found only inElymus. The S genome ofPseudoroegneria has almost always a dominant influence on the morphology of the taxa of which it is a component.Wang (1989) showed that the J genome inThinopyrum and the S genome have considerable homoeology, with a mean c-value of 0.35 in diploid SJ hybrids. A genetic coherence from S to SJ^e, J^e, J^eJ^b, and J^b can be expected, agreeing with the continuous morphologic variation pattern observed. Because of the absence of morphological discontinuities between the taxa,Pseudoroegneria (S),Elymus (SH, SY, sometimes with additional genomes),Elytrigia (SSH, SSHX), andThinopyrum (SJ, SJJ, J) are best treated as a single genus,Elymus, following the generic concept ofMelderis in Flora Europaea and Flora of Turkey. The basic genomic constituents ofElymus will then be the S and/or J genomes.Agropyron, with diploids, tetraploids, and hexaploids based on the P genome is morphologically distinct from other genera inTriticeae. In a few species ofElymus andPseudoroegneria, a P genome is an additional constituent. In these cases the P genome has a negligible morphological influence. Therefore, it seems reasonable to maintainAgropyron as a separate genus.     

Genetic recombination in the cephamycin producer,Streptomyces clavuligerus

Summary In order to study the mechanism of cephamycin production by streptomycetes and to use genetic recombination in strain development, we undertook genetic studies inStreptomyces lipmanii andS. clavuligerus. S. lipmanii crosses gave 0.005–1.3% prototroph-like colonies, but all segregated back to parental genotypes. Crosses ofS. clavuligerus resulted in lower frequencies of prototroph-like colonies, i.e., 0.00002–0.9%. In ade x ura and ade x his crosses, the recombinant progeny did not segregate back. In arg x ade and arg x his crosses, segregation occurred in about 50% of the progeny. These data demonstrate that true haploid recombinants occur in crosses ofS. clavuligerus. S. lipmanii yielded only heterokaryons and, therefore, is less suitable thanS. clavuligerus for further genetic study.     

Skeletal anatomy of the Late Cretaceous shark,Squalicorax (Neoselachii: Anacoracidae)

The paleobiology of the Cretaceous neoselachian shark,Squalicorax, has largely been based on isolated teeth. We examined partial and nearly complete skeletons of three species ofSqualicorax, S. falcatus (Aoassiz),S. kaupi (Agassiz), andS. pristodontus (Agassiz), that were collected from the U.S.A. These specimens suggest that the total body length (TL) ofS. falcatus typically measured 1.8–2.0 m, and probably did not exceed 3 m. Moderatesized individuals ofS. kaupi andS. pristodontus perhaps measured about 3 m TL. AlthoughS. pristodontus was the largest form among the three species examined, this taxon possessed a set of large jaws (with large but fewer teeth) relative to its body size compared toS. falcatus orS. kaupi. This suggests that tooth size is not an accurate indicator of the TL if one compares oneSqualicorax species to another. Neurocranial features suggest that the vision ofSqualicorax was not as acute as that of a contemporaneous macrophagous lamniform shark,Cretoxyrhina mantelli (Agassiz) , but olfaction ofSqualicorax may have been better thanC. mantelli. The morphology of placoid scales suggests thatSqualicorax was capable of fast swimming. New skeletal data support the view that the feeding dynamics ofSqualicorax was similar to the modern tiger shark (Galeocerdo Müller & Henle). The present data do not allow for exact ordinal placement, but, contrary to some previous interpretations,Squalicorax can be excluded from the Hexanchiformes and Orectolobiformes. The taxon should more appropriately be placed within the Lamniformes or Carcharhiniformes.      

Life-history and feeding habit ofTyphlodromus bambusae,a specific predator ofSchizotetranychus celarius (Acari: Phytoseiidae: Tetranychidae)

Studies on the life history and food habit ofTyphlodromus bambusae Ehara were carried out under aboratory conditions of 25±1°C, 60–80%rh and 159l:d.The egg-to-egg period of the predator which fed on eggs of the long-seta form ofSchizotetranychus celarius (Banks) was longer than those of the three phytoseiid species,Amblyseius eharai Amitai et Swirski,A. longispinosus (Evans) andA. paraki Ehara, which fed onTetranychus urticae Koch. The sex-ratio ofT. bambusae was not significantly different from those of the other three species. The long ovipositional period and the rather constant, low, reproductive rate observed inT. bambusae were remarkable.The intrinsic rate of natural increase (r _m) ofT. bambusae was 0.164 per day and it was very similar to ther _m of its prey,S. celarius. This observation supports the idea that there is a coincidence between the life-histories of spider-mite prey and their specific phytoseiid predators.Although females ofT. bambusae could feed on eggs ofAponychus corpuzae Rimando orSchizotetranychus recki Ehara which cohabit withS. celarius onSasa bamboo, their oviposition rate was lower than that onS. celarius eggs.Schizotetranychus celarius is thought to be a profitable prey species forT. bambusae, whileS. recki andA. corpuzae are only subsidiary, or alternative, prey.     

Segregation of male‐sterility alleles across a species boundary

Hybrid zones may serve as bridges permitting gene flow between species, including alleles influencing the evolution of breeding systems. Using greenhouse crosses, we assessed the likelihood that a hybrid zone could serve as a conduit for transfer of nuclear male‐sterility alleles between a gynodioecious species and a hermaphroditic species with very rare females in some populations. Segregation patterns in progeny of crosses between rare females of hermaphroditic Schiedea menziesii and hermaphroditic plants of gynodioecious Schiedea salicaria heterozygous at the male‐sterility locus, and between female S. salicaria and hermaphroditic plants from the hybrid zone, were used to determine whether male‐sterility was controlled at the same locus in the parental species and the hybrid zone. Segregations of females and hermaphrodites in approximately equal ratios from many of the crosses indicate that the same nuclear male‐sterility allele occurs in the parent species and the hybrid zone. These rare male‐sterility alleles in S. menziesii may result from gene flow from S. salicaria through the hybrid zone, presumably facilitated by wind pollination in S. salicaria. Alternatively, rare male‐sterility alleles might result from a reversal from gynodioecy to hermaphroditism in S. menziesii, or possibly de novo evolution of male sterility. Phylogenetic analysis indicates that some species of Schiedea have probably evolved separate sexes independently, but not in the lineage containing S. salicaria and S. menziesii. High levels of selfing and expression of strong inbreeding depression in S. menziesii, which together should favour females in populations, argue against a reversal from gynodioecy to hermaphroditism in S. menziesii.     

Technique d'élevage deChelonus contractus Nees. parasite dePhthorimea ocellatella Boyd.

Summary The Braconid,Chelonus contractus Nees, egg endoparasite ofPhthorimea ocellatella Boyd, in S.E. of France, presents only females in his progeny. Its breeding is easy with the help of the small wax moth:Gnorimoschema operculella Zell. The mass breeding is inspired from method that we established for the production ofMacrocentrus ancylivorus Roh.      

Influence of membrane structure on ion transport through lipid bilayer membranes

Summary Charge-pulse relaxation studies with the positively charged PV-K⁺ complex (cyclo-(d-Val-l-Pro-l-Val-d-Pro)₃) and the negatively charged lipophilic ion dipicrylamine (DPA^–) have been performed in order to study the influence of structural properties on ion transport through lipid bilayer membranes. First, the thickness of monoolein membranes was varied over a wide range using differentn-alkanes and slovent-free membranes. The thickness (d) of the hydrocarbon core of these membranes varied between 4.9 and 2.5 nm. For both transport systems the partition coefficient was found to be rather insensitive to variations ind. The same was valid for the translocation rate constantk _MS of PV-K⁺, whereas a strong increase of the translocation rate constantk _i of DPA-with decreasingd was observed. In a further set of experimental conditions the structure of the lipids, such as number and position of the double bonds in the hydrocarbon chain and its chain length as well as the nature of the polar head group, was varied. The translocation constantk _MS of PV-K⁺ transport was found to be much more sensitive to these variations thank _i of DPA-.Much larger variations ink _i andk _MS were observed in membranes made from lipids with ether instead of ester linkages between glycerol backbone and hydrocarbon chain. The results are in qualitative agreement with the surface potentials of monolayers made from corresponding lipids. Increasing amounts of cholesterol in membranes of dioleoylphosphatidylcholine caused a strong decrease ofk _MS (PV-K⁺), whereask _i was found to be rather insensitive to this variation.In monoolein membranes cholesterol causes a decrease ofk _MS up to sixfold and a increase ofk _i up to eightfold. The partition coefficient of DPA^– was insensitive to cholesterol, whereas of PV-K⁺ was found to decrease about eightfold in these membranes. The influence of cholesterol onk _MS is discussed on the basis of viscosity changes in the membrane and the change ink _i of DPA^– and of PV-K⁺ on the basis of a possible change of the dipole potential of the membranes. The other sterols, epicholesterol and ergosterol cause no change in the kinetics of the two probes.The different influence of membrane properties like thickness, viscosity, and dipole potential on the two transport systems is discussed under the assumption that the adsorption planes of the two probes have different positions in a membrane. Possibly because of a larger hydrophobic interaction, the adsorption plane of PV-K⁺ is located more towards the hydrocarbon side and that of DPA^– more towards the aqueous side of the dipole layer.     

Environmental effects on Segregation-distorter in Drosophila melanogaster: Irradiation of SD-72 at the onset of spermatogenesis

To ascertain the effect of irradiation at the onset of spermatogenesis on Segregation-distorter, irradiation treatments were administered to very late third instar male SD larvae. Part of the experimental and control groups were stored. The first four daily broods from unstored irradiated males exhibited depressed k values and aberration products. The percentage of aberrations observed per sperm batch is inversely correlated with the k values exhibited. The SD mechanism appeared to be most sensitive to irradiation prior to or at Prophase I. Using aberration products as an index, stored males transfer few sperm which were in meiotic or premeiotic stages at the time of treatment. The induction of these aberrations affected the action of the SD mechanism very little. The SD-bearing exceptional chromosomes were 0.9 of the total exceptions recovered. Lack of mating activity depressed the drive of SD in both irradiated and control groups. Prolongation of spermiogenesis may allow recovery of SD+ gametes which were rendered temporarily dysfunctional.This work was completed at Michigan State University during the tenure of a National Institutes of Health Fellowship and partially supported by a grant to Dr. Armon F. Yanders from the U.S. Atomic Energy Commission (Contract AT (11-1) 1933)     

Effects of fumarate,l-malate,and anAspergillus oryzae fermentation extract ond-lactate Utilization by the ruminal bacteriumSelenomonas ruminantium

Growth ofSelenomonas ruminantium HD4 in medium that contained 21mm d-lactate was stimulated to varying degrees by 10mm l-malate, 10mm fumarate, and 2% (v/v)Aspergillus oryzae fermentation extract (Amaferm). Amaferm treatment caused the greatest growth stimulation. Initial uptake rates (30s) and long-term uptake rates (30 min) ofd-lactate by whole cells ofS. ruminantium were increased in the presence of 10mm l-malate. Amaferm (25 l/ml) also stimulated long-term uptake rates ofd-lactate, whereas fumarate had no effect. Initial uptake ofd-lactate was depressed in the presence of fumarate or Amaferm. When eitherl-malate, fumarate, or Amaferm was included in thed-lactate growth medium, a homosuccinate fermentation resulted and an inverse relationship was observed between growth (protein synthesis) and succinate production. Recent research demonstrated that Amaferm containsl-malate, and this dicarboxylic acid may be involved in stimulatingd-lactate utilization byS. ruminantium.     

Ultrastructure of the plasmodial slime moldPerichaena vermicularis

Summary Mature plasmodia ofPerichaena vermicularis require a light period to induce sporulation. In this paper the ultrastructure and acid phosphatase localization of the mature plasmodium ofPerichaena vermicularis are investigated. Acid phosphatase is localized in vacuoles containing remnants of bacteria and cell organelles. Morphological and histochemical evidence support the interpretation that these vacuoles constitute two types of lysosomes called respectively heterophagic and autophagic vacuoles.Coated vesicles which apparently originate from smooth endoplasmic reticulum are dispersed throughout the plasmodium and frequently associated with lysosomes. Several dumbbellshaped mitochondria are observed in the plasmodium at the onset of fruiting but not during later stages of plasmodiocarp development. Cytoplasmic microtubules are identified inPerichaena vermicularis. Some of these are closely associated with microfilaments.This work was supported by National Science Foundation grants (GB-5884 and GB-8537) to Dr.Ian K.Ross, NSF grant (GB 12371) to Dr.James Cronshaw, and an NSF Traineeship (GZ 445 and 796) to I.Charvat.This constitutes a portion of a thesis presented to the Regents of the University of California by the first author in partial fulfillment of the requirements for the Ph. D. degree.     

Die Abhängigkeit der Reizzeiten bei der elektrischen Erregung von der Länge der erregten Gebilde

Zusammenfassung An Vorticellen lassen sich zwei sehr verschiedene Chronaxien nachweisen, kurze, die man aus gewissen Gründen dem Köpfchen, und lange, die man dem Stiel zuordnen kann. Die Chronaxien verhalten sich zueinander ungefähr wie die Quadrate der Längen von Köpfchen und Stiel.Bei Internodialzellen vonNitella verkürzt sich beim Verkürzen der Zellänge durch Abbinden die Chronaxie ungefähr proportional dem Quadrat der Zellänge, wenn sich die Kathode immer an demselben intakten Zellende befindet.Diese Befunde stützen die Ansicht vonUmrath (1925, 1928, 1942, 1959), daß die Reizzeiten bei der elektrischen Erregung den Quadraten der Zellängen proportional sind, wobei sich aber für die in der Theorie der elektrischen Erregung vonNernst (1899, 1908) als Diffusionskoeffizient eingeführte Größek ein Zahlenwert ergibt, der für einen Diffusionskoeffizienten zu groß, beiNitella viel zu groß ist. Man kann nachUmrath (1928, 1942, 1959)k als Beweglichkeit elektrisch polarer, grenzflächenaktiver Molekeln im Plasmalemma interpretieren und so die mathematischen Formulierungen der Theorie vonNernst (1899, 1908) und vonHill (1910) übernehmen.Beim Vergleich verschiedener Organismen mit sehr verschiedenen Zellängen zeigt sich eine Zunahme der Chronaxien mit zunehmenden Zellängen, aber nicht proportional den Quadraten der Zellängen, so daßk mit zunehmender Zellänge zunimmt. Das wird vonUmrath (1959) dahingehend gedeutet, daß einer hohen Beweglichkeit grenzflächenaktiver Substanzen im Plasmalemma mit zunehmender Zellgröße zunehmender Selektionswert zukommt. Extrem großek-Werte kommen bei den Skelettmuskeln und Nerven der Wirbeltiere vor, bei denen sie auch für eine rasche Erregungsleitung von Bedeutung sein dürften.

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Stimulation-times in electrical excitation as depending from the length of the exited units

Summary In Vorticellae two very different chronaxies can be demonstrated, short ones, which for certain grounds can be ascribed to the head, and long ones, which can be ascribed to the stalk. The chronaxies are approximately in the same proportion as the squares of the lengths of the head and stalk.If internodial cells ofNitella are shortened by tying them off, the chronaxie is shortened about as the square of the cell-length, provided that the cathod is always situated on the same, intact end of the cell.These findings support the view ofUmrath (1925, 1928, 1942, 1959), that in electrical excitation necessary times of current flow are proportional to the squares of the cell-lengths. But if one calculates the numerical value of the diffusion-coefficientk, introduced byNernst (1899, 1908) in the equations of his theory of electrical excitation, it is too great, inNitella much too great, for a diffusion-coefficient. AfterUmrath (1928, 1942, 1959) one may interpretek as the mobility of electrically polar, surfaceactive molecules in the plasmalemma and in this way take over the mathematical formulations of the theory ofNernst (1899, 1908) andHill (1910).In comparing different organisms with widely different cell-lengths it results an augmentation of the chronaxie with increasing cell-length, but not proportional to the square of the cell-length, so thatk increases with increasing cell-length.Umrath (1959) explains this by assuming, that with increasing cell-length the selection-value of a high mobility of surfaceactive substances in the plasmalemma is increased. Extremely great values ofk are encountered with skeletal muscles and nerves of vertebrates, where they may be of importance for fast conduction of excitation.

     

Ultrastructure of the male nephridium and its role in spermatophore formation in spionid polychaetes (Annelida)

Summary The mature male nephridia ofPolydora ligni andP. websteri (Polychaeta: Spionidae) are segmental organs composed of a ciliated nephrostome connected to a nephridial canal that crosses the intersegmental septum, expands into a large modified part extending dorsally through the coelom and subsequently narrows into a canal terminating in a dorsal nephridiopore. The nephridial canal is ciliated throughout and is composed of several cell types. Cells in the expanded region of the nephridia of both species contain large urn-shaped depressions filled with long microvilli. InP. ligni, one section of a nephridium contains cells packed with electron-dense granules that are not observed inP. websteri.The spermatophores ofPolydora ligni are composed of a central sperm mass surrounded by a layer of randomly oriented tubules that form a capsule around the sperm and taper into a long thin tail. These tubules are identical in dimensions to the microvilli present in parts of a nephridium and apparently are derived from these microvilli. The spermatophore capsule ofP. websteri is composed of similar tubules also presumed to originate from nephridial microvilli.The microvilli in nephridia of both species are surrounded with a glycocalyx that may function as an adhesive to hold the spermatophore capsule together. This glycocalyx may also function as a species specific message when encountered by a receptive female.Contribution Number 179 from Harbor Branch Foundation, Inc.     

Kritsche Betrachtungen zur Nomenklatur argentinischer Wildkartoffeln

Summary Continuing the critical publications on the nomenclature of the Argentine wild potatoes, set on in 1956, now the results of 5 years' studies of the seriesAcaulia are discussed. This series is to be found in the highlands of the Cordilleras and its vegetation limit is at about 4700 m above sea-level. The frost-resistance ofS. acaule andS. aemulans is remarkably high (up to minus 10°). ForS. acaule cytological determinations have proved again the already known number 2n=48, besides this in the province of Jujuy a species with 2n=36 has been found, being probably a hybrid ofS. acaule andS. alticolum. This species with 36 chromosomes is increasingly spreading in certain arid areas in an altitude of 4000 m. ForS. aemulans the chromosome number 2n=24 is published for the first time. Reciprocal crosses under greenhouse conditions betweenS. aemulans (2n=24) andS. acaule (2n=48) showed no success. In opposition to the view ofHawkes the author insists onS. aemulans being a good species, endemical for the arid mountains of Famatina and Ambato in the provinces of La Rioja and Catamarca. Having been collected in 1907 for the last time, nowS. aemulans has anew been found by the author in the Famatina mountains.As toS. acaule and its numerous varieties and related species the author holds the following opinion: The termsS. depexum, Schreiteri, punae, subexinterruptum, checcae, caulescens, chorruense established byBitter, Bukasov, Juzepzuk, andHawkes, are superfluous, the real range of variability is moreover much greater. To illustrate this point of view some examples were set.By its valuable resistance-genes againstRhizoctonia, frost, and Virus,S. acaule, at present, has gained considerable importance for plant breeding. For this reason we think it the more necessary to elucidate the systematical and cytological problems of the whole SeriesAcaulia.

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Mit 8 Abbildungen     

X-irradiation of theDrosophila male and its effect on the number of sperm transferred to the female

Summary Experiments were carried out to determine the number of sperm transferred by the maleDrosophila after X-irradiation. Acute doses (1000 r/min) of 5,000 r, 25,000 r and 50,000 r delivered to the male results in reductions of some 20–25%, 60–65%, and 85–90%, respectively, in the number of sperm scored in the ventral receptable of inseminated females. It appears, further, that sperm in ejaculates of relatively small size (50 or fewer) from irradiated as well as unirradiated males distribute themselves such that 20–50% or more found in the spermathecae. The bearing of this observation on the apparent 1:1 sperm: progeny ratio reported byPeacock andErickson (1965) from ejaculates with low sperm number is noted.Supported by National Science Foundation Grant GB-3117.     

The adaptive significance of mate guarding in the soapberry bug,Jadera Haematoloma (Hemiptera: Rhopalidae)

Male soapberry bugs (Jadera haematoloma)face severe mating competition at the northern edge of their range due to male-biased adult sex ratios. Copulations lasting up to 11 days may serve a mate guarding function (encompassing four or more ovipositions), but copulation duration is highly variable, with some pairings lasting as little as 10 min. Data were gathered to describe factors that influence the reproductive costs and benefits of prolonged copulation. Estimated copulation durations (mean ± SD) were 20 ± 23 h in the lab and 50 ± 8 h in the field and were only weakly affected by sex ratio. Females mated for 5 min produced as many fertile eggs as those mated for 600 min laid; they became depleted of fertile sperm after about 25 days. In twicemated females, the first male's paternity was reduced by about 60%, and all females (N = 13) whose mates were removed experimentally mated again within an average of 6 min. The outcome of sperm competition on a perclutch basis was not highly predictable. The possibility of increased sperm displacement in longer copulations was not tested. Males often guarded females during oviposition and successfully defended them from intruding single males by recopulating. Such intrusions occurred in the majority of oviposition attempts observed in nature. Even though most females mated promiscuously, in a focal aggregation with a mean sex ratio of 2.2 ± 0.4 males/female, the interval between matings by males was commonly several days. Males appeared to respond facultatively to several aspects of the distribution and availability of females. The intensities of mating competition and sperm competition indicate that monogamous mate guarding should be favored over nonguarding in nature. Unpredicted brief. pairings may result from assessment by males of female reproductive value or of their own physical condition, or from female resistance.     

The process of population increase and patterns of resource utilization of two spider mites,Oligonychus ununguis (Jacobi) andPanonychus citri (McGregor), under experimental conditions (Acari: Tetranychidae)

Summary Pattern of population growth and characteristics of habitat utilization and of migration by two species of spider mites were studied under experimental conditions. The population growth ofOligonychus ununguis (Jacobi) on a chestnut occurred only on a single mite-release leaf over a long period, and few individuals moved away. Most of the 2nd progeny generation females of this species emigrated from the mite-release leaf as well as the sapling by means of ballooning threads. During this growth period, population density on the mite-release leaf levelled off, whereas that on the sapling increased. In contrast, the foundress ofPanonychus citri (McGregor) on citrus actively moved over several neighbouring leaves, and until the 2nd progeny generation females emerged, individuals were distributed over all the sapling leaves by means of walking. Emigration from the sapling was not observed until the 2nd progeny females emerged, and after that the mites emigrated by means of ballooning threads. The population density ofP. citri on the sapling levelled off and was rather decreased on the mite-release leaf at the time of mite emigration. Comparing the changing pattern of the relative degree of aggregation (m ^*/m) measured in two different units between these two species, the pattern ofm ^*/m in 1 cm² on the mite release leaf inO. ununguis resembled that of the unit of leaves on the sapling inP. citri. This result as well as behavioural observations indicate that migration ofO. ununguis is the movement from leaf to leaf and that ofP. citri from sapling to sapling. It is, therefore, concluded that the boundary of the microhabitat is a single leaf forO. ununguis but sapling or foliage forP. citri. This work was presented in Annual Meeting of Jap. Soc. Appl. Ent. Zool., 1981 in Okayama.     

Aliphatic 1,2-alkanolamines — Inhibitors ofβ-glucanase fromCandida utilis

Aliphatic 1,2-alkanolamines inhibitedβ-glucanase fromCandida utilis. The highest inhibitory effect was observed with 1-dodecylamino-3-chloro-2-propanol (K _i=1.0μmol/L) and it was much higher than that ofd-glucono-δ-lactone. Simple 1,2-alkanolamines, like 2-aminoethanol or 2-methylaminoethanol, did not exhibit any significant inhibitory effect.     

Experimental documentation of natural hybridization inCactaceae: Origin of Lloyd's Hedgehog Cactus,Echinocereus ×lloydii

The origin ofEchinocereus ×lloydii Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus Engelm. (a species of claret-up cactus) andE. dasyacanthus Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F₁ hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F₂ generation hybrids were also obtained. The known F₁ hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically.     

A model for marker-assisted selection among single crosses with multiple genetic markers

 Trait means of marker genotypes are often inconsistent across experiments, thereby hindering the use of regression techniques in marker-assisted selection. Best linear unbiased prediction based on trait and marker data (TM-BLUP) does not require prior information on the mean effects associated with specific marker genotypes and, consequently, may be useful in applied breeding programs. The objective of this paper is to present a flanking-marker, TM-BLUP model that is applicable to interpopulation single crosses that characterize maize (Zea mays L.) breeding programs. The performance of a single cross is modeled as the sum of testcross additive and dominance effects at unmarked quantitative trait loci (QTL) and at marked QTL (MQTL). The TM-BLUP model requires information on the recombination frequencies between flanking markers and the MQTL and on MQTL variances. A tabular method is presented for calculating the conditional probability that MQTL alleles in two inbreds are identical by descent given the observed marker genotypes (G ^k _obs) at the kth MQTL. Information on identity by descent of MQTL alleles can then be used to calculate the conditional covariance of MQTL effects between single crosses given G ^k _obs. The inverse of the covariance matrix for dominance effects at unmarked QTL and MQTL can be written directly from the inverse of the covariance matrices of the corresponding testcross additive effects. In practice, the computations required in TM-BLUP may be prohibitive. The computational requirements may be reduced with simplified TM-BLUP models wherein dominance effects at MQTL are excluded, only the single crosses that have been tested are included, or information is pooled across several MQTL. Received: 22 June 1997 / Accepted: 25 February 1998