Nearest Neighbor Classification Rule for Mixtures of Discrete and Continuous Random Variables

In this paper very simple nonparametric classification rule for mixtures of discrete and continuous random variables is described. It is based on the method of nearest neighbor proposed by Cover and Hart (1967). The bounds on the limit of the nearest neighbor rule risks are given. Both lower and upper bound depend on the Bayes risk and the loss function. Finally the method is compared with other existing methods on some practical data set.     

Embryo culture of Medicago scutellata and M. sativa

Resistance to the alfalfa weevil (Hypera postica (Gyllenhal)) and the potato leafhopper (Empoasco fabae (Harris)) is lacking in cultivated alfalfa. However, a closely related annual Medicago, Medicago scutellata, possesses dense glandular stem and leaf hairs which provides a mechanism for resistance. Several attempts have been made at transfering the glandular haired traint from M. scutellata to perennial alfalfa with limited success. Earlier studies have shown that one reason for the lack of success is embryo abortion. Therefore, this study was initiated to observe zygotic embryo-genesis and to develop an embryo rescue technique for M. scutellata and M. sativa. Observations of zygotic embryogenesis showed that the two species are similar in morphology and can be described from youngest to oldest as globular, heart, torpedo, and hook shaped embryos. M. sativa embryos are smaller than M. scutellata embryos and develop three to four days later. Self pollinated M. scutellata (PI 307446) and sib mated M. sativa (Saranac AR) embryos were cultivated on Murashige and (2,4-D), indolacetic acid (IAA), 6-benzylaminopurine (BAP), and kinetic (KIN). Embryos from both species were also cultured on Schenk and Hildebrandt's (SH) basal medium with the addition of L-glutamine and L-proline. The experimental design was a completely randomized factorial for each experiment. Heart and torpedo shaped embryos from M. scutellata grew best (27.5% plantlet recovery) when cultured on MS medium with 0.05 mgl^-1 of both IAA and BAP. After 15 to 30 days on this medium, the embryos had only developed shoots. Therefore, it was necessary to transfer the shoots to MS basal medium without phytohormones for rooting. Rooting occurred in 15 to 30 days and the plantlets could be acclimatized to soil within 2 to 4 weeks. M. sativa embryos grew best (31% plantlet recovery) on SH medium with 50 mM L-glutamine. M. sativa embryos developed both shoots and roots on this medium. This information may now be applied to the development of an embryo culture method for recovering insect resistant hybrids between M. scutellata and M. sativa. Disclaimer statement: Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products that may also be suitable.     

The use of periphyton communities for nutrient removal from polluted streams

The results of experiments on the efficiency of periphyton communities for nutrient removal from polluted streams in a continuous flow-through are given. The artifical stream (5 m × 0.7 m × 0.5 m) was made of wood, with silon (a kind of nylon) screens, as a substratum for periphyton growth. The elimination of nutrients was monitored by ammonium, nitrite, nitrate and orthophosphate analyses. In addition, the elimination of organics and the decrease in trophic state were determined. During two field experiments a marked elimination of nitrogen and phosphorus was demonstrated. The maximum efficiency of ammonium and orthophosphate removal was 80% and 70%, respectively. Organic removal reached 35% (C.O.D._Mn-Kubel) and 54% (B.O.D.₅). Inorganic and organic nutrient elimination caused significant changes in periphyton community structure in the outflow portion of the through, evaluated by the saprobic index and the similarity coefficient. The experiments confirmed that periphyton communities are a useful means of nutrient removal from polluted streams.     

Inheritance of a vestigial wing mutation in the alfalfa weevil, Hypera postica

Alfalfa weevils (Hypera postica (Gyllenhal)) with vestigial hind wings were discovered in a population from Wageningen, the Netherlands, and two populations from the United States—an eastern weevil strain from Beltsville, Maryland and an Egyptian weevil strain from Atascadero, California. Such a mutant was absent from 23 other populations surveyed in the United States—three from eastern, seven from western, and 13 from Egyptian weevil strains. This mutation is due to a dominant autosomal gene with normal-wing individuals as recessive. The mutant gene can be transferred from eastern weevil to the western weevil strain. The short-wing trait may be useful for genetic manipulation to control the alfalfa weevil.

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Résumé Des H. postica aux ailes postérieures vestigiales ont été découverts dans une population de Wageningen (Pays Bas) et deux des USA—une lignée orientale de Beltsville (Maryland) et une lignée de H. brunneipennis d'Atascadero (Californie). Ce mutant était absent de 23 autres populations examinées aux USA: 3 de l'est, 7 de l'ouest et 13 de H. brunneipennis. Cette mutation est due à un gène dominant antosomal avec aile normale comme récessif. Le gêne mutant peut être transféré des lignées orientales aux lignées occidentales. Le caractère aile courte peut être pratique pour les manipulations génétiques destinées à maîtriser les populations d'H. postica.

     

Fine root demography in alfalfa (Medicago sativa L.)

In perennial forages like alfalfa (Medicago sativa L.), repeated herbage removal may alter root production and mortality which, in turn, could affect deposition of fixed N in soil. Our objective was to determine the extent and patterns of fine-diameter root production and loss during the year of alfalfa stand establishment. The experiment was conducted on a loamy sand soil (Udorthentic Haploboroll) in Minnesota, USA, using horizontally installed minirhizotrons placed directly under the seeded rows at 10, 20, and 40 cm depths in four replicate blocks. We seeded four alfalfa germplasms that differed in N₂ fixation capacity and root system architecture: Agate alfalfa, a winter hardy commercially-available cultivar; Ineffective Agate, which is a non-N₂-fixing near isoline of Agate; a new germplasm that has few fibrous roots and strong tap-rooted traits; and a new germplasm that has many fibrous roots and a strongly branched root system architecture. Video images collected biweekly throughout the initial growing season were processed using C-MAP-ROOTS software.More than one-half of all fine roots in the upper 20 cm were produced during the first 7 weeks of growth. Root production was similar among germplasms, except that the highly fibrous, branch-rooted germplasm produced 29% more fine roots at 20 cm than other germplasms. In all germplasms, about 7% of the fine roots at each depth developed into secondarily thickened roots. By the end of the first growing season, greatest fine root mortality had occurred in the uppermost depth (48%), and least occurred at 40 cm (36%). Survival of contemporaneous root cohorts was not related to soil depth in a simple fashion, although all survivorship curves could be described using only five rates of exponential decline. There was a significant reduction in fine root mortality before the first herbage harvest, followed by a pronounced loss (average 22%) of fine roots at the 10- and 20-cm depths in the 2-week period following herbage removal. Median life spans of these early-season cohorts ranged from 58 to 131 days, based on fitted exponential equations. At all depths, fine roots produced in the 4 weeks before harvest (early- to mid-August) tended to have shorter median life spans than early-season cohorts. Similar patterns of fine root mortality did not occur at the second harvest. Germplasms differed in the pattern, but not the ultimate extent, of fine root mortality. Fine root turnover during the first year of alfalfa establishment in this experiment released an estimated 830 kg C ha^–1 and 60 kg N ha^–1, with no differences due to N₂ fixation capacity or root system architecture.     

Molecular integrity of monoclonal antibodies produced by hybridoma cells in batch culture and in continuous-flow culture with integrated product recovery

The molecular integrity of monoclonal antibodies (MCAB) produced by murine hybridoma cell line TB/C3 was studied in batch and continuous-flow cultures. In batch culture, one band of MCAB was detected initially by Western blotting of sodium dodecyl sulfate (SDS)-polyacrylamide gels run under unreduced conditions, but heterogenous MCAB bands appeared as the culture aged. The latter were due to the degradation of MCAB by proteases active at the neutral pH of the culture. The deleterious effect of proteases was minimized in the continuous-flow cultures which were integrated for product recovery. The MCAB of high quality was purified over 26 days from a culture grown at a dilution rate of 0.025 h(-1) (experiment 1). However, at a lower dilution rate of 0.015 h(-1) (experiment 2), the integrity of MCAB was compromised after the initial 13 days of culture. This was shown to be due to the variation in the carbohydrate content of MCAB produced, as judged by the increased sialylation of heavy chains and the varied reactivity of MCAB with lectins (Maackia amurensis agglutinin, Galanthus nivalis agglutinin, and Datura stramonium agglutinin) as the age of the culture increased. The concentration of the purified MCAB samples by enzyme-linked immunosorbent assay (ELISA) (used normally) was usually higher than that estimated by absorbance at 280 nm. Best correlation between the two methods (ELISA-280 nm ratio of 1.02-1.25) was obtained with experiment 1 samples. This ratio increased in experiment 2 and batch culture samples as the heterogeneity of MCAB produced increased, being 1.03-2.94 and 2.53-4.62, respectively. Therefore, ELISA overestimated MCAB concentration when the molecular integrity of the latter was compromised. The ELISA-A(280) nm ratio might hence provide a useful indicator for assessing the quality of MCAB produced. Comparison of SDS-polyacrylamide gels stained with Coomassie Brilliant Blue R and silver showed that the former correlated better with the MCAB activity stain, whereas the silver stained both the protein- and carbohydrate-rich components. Comparison of the patterns produced with these two stains might therefore offer another parameter to monitor the overall integrity of MCAB produced. Finally, the data presented have important implications on the validity of using long-term and intensive cultures for generating MCAB because such cultures would be subjected to the additive effects reported for batch and continuous modes of growth. (c) 1993 John Wiley & Sons, Inc.     

Effects of media composition on substrate removal by pure and mixed bacterial cultures

Continuous culture experiments with identical experimental designs were run with a mixed microbial community of activated sludge origin and an axenic bacterial culture derived from it. Each culture received 2-chlorophenol (2-CP) at a concentration of 160 mg/L as COD and L-lysine at a concentration of 65 mg/L as COD. A factorial experimental design was employed with dilution rate and media composition as the two controlled variables. Three dilution rates were studied: 0.015, 0.0325, and 0.05 h^–1. Media composition was changed by adding four biogenic compounds (butyric acid, thymine, glutamic acid and lactose) in equal COD proportions at total concentrations of 0, 34, 225, and 1462 mg/L as COD. The measured variables were the effluent concentrations of 2-CP as measured by the 4-aminoantipyrene test and lysine as measured by the o-diacetylbenzene procedure. The results suggest that community structure and substrate composition play important roles in the response of a microbial community to mixed substrates. The addition of more biogenic substrates to the axenic culture had a deleterious effect on the removal of both lysine and 2-CP, although the effect was much larger on lysine removal. In contrast, additional substrates had a positive effect on the removal of 2-CP by the mixed community and much less of a negative effect on the removal of lysine. The dilution rate at which the cultures were growing had relatively little impact on the responses to the additional substrates.Abbreviations COD chemical oxygen demand - 2-CP 2-chlorophenol - DOC dissolved organic carbon - MDL method detection limit - SS suspended solids     

Effect of oxygen on denitrification in continuous chemostat culture withComamonas sp SGLY2

Continuous cultures ofComamonas sp SGLY2 were grown anaerobically prior to establishing steady states at different oxygen flow rates. At a low oxygen transfer rate, no dissolved oxygen accumulated in the medium and all nitrate was reduced to dinitrogen. Concurrently with the increase of dissolved oxygen concentration in the liquid phase, the rate of denitrification decreased. However, at a dissolved oxygen concentration near saturation (33 mg L^–1), a part of the electron flow always diverted to nitrate with production of dinitrogen: the aerobic denitrification rate was equivalent to 35% of that calculated under anaerobic conditions. These experiments reflected the co-utilization of oxygen and N-oxides and the production of dinitrogen, up to saturated conditions, which implied synthesis and activity of the four denitrifying enzymes under various aeration conditions.     

Improved correlation between soil exchangeable K and plant K contents on a tissue water basis

In acid volcanic soils, plant roots are thought to be injured by acidity (low pH) and/or solubilized aluminium (Al) ions. An attempt was made to separate the effects of low pH from those of Al on the elongation and viability of alfalfa (Medicago sativa L.) radicles in water culture. Root elongation was irreversively curtailed by 20 hours treatment at pH 4.0 without Al or 20 mmol m^-3 Al at pH 5.0. Viability of surface cells of root tips was detected as a degrading activity of fluorescein diacetate (FDA) by cellular esterases and subsequent accumulation of derived fluorescein within cells. Large numbers of the surface cells lost their viability after four hours exposure at the low pH. In contrast, surface cells maintained both FDA degrading activity and ability to accumulate fluorescein 20 h after initial exposure to the Al solution (20 mmol Al m^-3, pH 5.0). These results suggest that there are some significant differences in the mechanisms of phytotoxicity to alfalfa root between the two stress factors.     

Coat protein polymerization of alfalfa mosaic virus strain VRU

The association behaviour of the coat protein of alfalfa mosaic virus strain VRU was studied by sedimentation analysis and electron microscopy. The results of this study were compared with the data obtained from similar studies with the coat protein of strain 425 (Driedonks et al., 1977). In the depolymerized state VRU protein is likely a dinier of the 24,050 molecular weight polypeptide chain. The main association product is a tubular structure with a diameter of about 180 Å. The optimum conditions for the reaction were polyphosphate-containing buffer at pH 6·5. Optical diffraction analysis of negatively stained specimens revealed a helical arrangement of the protein subunits in these assemblies. The same type of reaction product was found when the association reaction was carried out in the presence of polynucleotides. The length of the VRU particles is abnormally long compared to other alfalfa mosaic virus strains. This phenomenon can be ascribed to the tendency of the protein to polymerize into tubular rather than spherical particles.