Materials forPythium flora of Japan VIII Two species ofPythium:P. pyrilobum andP. oligandrum

Two species ofPythium (P. pyrilobum, P. oligandrum) having spherical sporangia with complex subglobose elements were isolated from the crown of creeping bentgrass [Agrostis palustris (cv. Penncross)] and from vegetable field soil, respectively. They are reported for the first time in Japan.     

Characterization of two morphological groups of isolates ofPythium ultimum var.ultimum in a vegetable field

Comparisons were made between two morphological groups ofPythium ultimum var.ultimum strains isolated in a vegetable field in Japan. The groups were distinguished as having smaller or larger sexual organs by the sizes of their antheridia and oogonia. Morphological study indicated that the two groups comprised a single taxon,P. ultimum var.ultimum, by the current taxonomical keys. The smaller group grew faster in the lower temperature range of 4–15°C, whereas the larger group grew faster in the higher temperature range of 25–37°C. Random amplified polymorphic DNA (RAPD) and isozyme analyses revealed genetic dissimilarity between the two groups. Cluster analysis of the isozyme banding patterns with four otherPythium spp. demonstrated that the genetic dissimilarity between the two groups was equivalent to species level. In the field survey, the smaller group was frequently detected in February, May and September but not in July, while the larger group was detected mainly in July and September. The two groups were not distinguishable by their pathogenicity to spinach seedlings.     

Materials forPythium flora of Japan. X. Occurrence,identification and seasonality ofPythium spp. in three pond waters and mud soils in Osaka

Seasonal fluctuations ofPythium species in three pond waters and mud soils in Sakai, Osaka, were studied for periods of two years and 14 months, respectively. Thirteen species and four groups were isolated from the pond waters while nine species and three groups were obtained from the mud soils. The highest frequency and total number of species were recorded in the cold and moderately warm seasons and the lowest in summer. Most of the species isolated from the pond waters have been previously recorded from aquatic habitats.     

First records of Pythium aquatile and P. macrosporum isolated from soils in Japan

Pythium aquatile and P. macrosporum were isolated from the soil of a cultivated field in Gunma Prefecture and a forest in Nagano Prefecture for the first time in Japan. Their morphological characteristics are described, and their pathogenicity and taxonomy are discussed.     

Acremonium-like submerged conidiation inPaecilomyces nostocoides andP. lilacinus

Paecilomyces nostocoides, in which conidia of smaller or larger sizes appear in chains, was newly isolated from Japan. In addition to the typicalPaecilomyces-type conidiation, the Japanese isolate showed additionalAcremonium-like submerged conidiation in and/or on some agar media. The submerged conidiation was also observed in the ex-type strains, but not in the type specimens ofP. nostocoides. The same submerged conidiation was observed inP. lilacinus, the species most similar toP. nostocoides. The species definitions ofP. nostocoides andP. lilacinus were emended to include the submerged conidiation.Paecilomyces-type conidia were uninucleate in bothP. nostocoides andP. lilacinus. Paecilomyces nostocoides andP. lilacinus had the Q-10(H₂) ubiquinone system.     

Virulence ofPythium spp. isolated from pond water

Pre-emergence damping-off tests indicate that Pythiumspp. from pond water can be divided into two categories: avirulent Pythium (P. diclinum, P. marsipium, P. middletonii, P. monospermum, P. pleroticum, P. undulatum)and weakly virulent Pythium (P. catenulatum, P. coloratum, P. dissotocum, P. papillatum, Pythium Group F, Pythium group HS, Pythium group P, Pythiumgroup T). Post-emergence damping-off tests indicate that the pythia tested can also be divided into three categories: avirulent Pythium (P. catenulatum, P. dissotocum, P. marsipium, P. monospermum, P, papillatum, P. pleroticum, P. undulatum, Pythium group F, Pythium group T),weakly virulent Pythium (P. coloratum, P. diclinum, P. middletonii, Pythiumgroup P and moderately virulent Pythium (Pythium group HS).     

大气CO2浓度升高对稻田土壤线虫群落的影响

本试验利用无锡稻 麦轮作FACE系统研究平台 ,开展了稻田土壤线虫群落对大气CO2 浓度升高响应的研究。实验中共观测到线虫 2 7科 4 0属 ,其中短腔属 (Brevibucca)、茎属(Ditylenchus)和垫刃属 (Tylenchus)为优势属。拔节期稻田土壤线虫总数、食细菌线虫和捕食 /杂食线虫对大气CO2 浓度升高表现出正响应。食真菌线虫在拔节期和抽穗期对CO2 浓度升高表现出负响应 ,成熟期捕食 /杂食线虫对CO2 浓度升高表现出负响应。在FACE条件下 ,植物寄生线虫的潜根属 (Hirschmanniella)和散香属 (Boleodorus)线虫数量显著增加 ,对CO2 浓度升高敏感     

Conidiomatal development ofPestalotiopsis guepinii andP. neglecta on leaves ofGardenia jasminoides

This study has clarified the conidiomatal development ofPestalotiopsis guepinii andP. neglecta on leaves ofGardenia jasminoides. Acervuli ofP. guepinii andP. neglecta developed in a similar manner, in two stages. In the first stage, cells aggregated, the central cell of the aggregates gradually disappeared, and the cells of inner layer produced numerous conidia. This conidioma was pycnidium-like in appearance, and in some cases ceased development at this stage. In the second stage, the upper layer of the pycnidium-like structure broke open, forming an acervular conidioma.     

Cytological characterization of heterochromatin and rDNA inPinus radiata andP. taeda

Fluorochrome C-banding ofPinus radiata andP. taeda metaphase chromosomes showed many pericentromeric DAPI bands and interstitial CMA bands inP. radiata, and centromeric and interstitial CMA bands inP. taeda. Giemsa C-band patterns differed between the species with centromeric bands inP. radiata but no consistent bands inP. taeda. A karyotype ofP. radiata was developed based on banding patterns that distinguished all but two of the 12 pairs of chromosomes. In situ hybridization (ISH) using probes for high-copy ribosomal DNA (rDNA) showed 10 pairs of 18S–25S sites and two pairs of 5S sites in both species. Most of the sites were interstitial or centromeric.     

Induced apogamous sporophytes inPteris dispar andP. semipinnata,and the meiotic behavior in their sporocytes

Spores ofPteris dispar andP. semipinnata were aseptically cultured in flasks for apogamous sporophyte induction. Calli or cell colonies similar to calli were induced in cultures supplemented with hormones. Sporophytic leaves subsequently developed from them in hormone-free medium and the young sporophytes were raised into plants with sporangia. Since the wild-type plants having 116 chromosomes are tetraploid, the sporophytic plants originating from spores would appear to be diploid (dihaploid). In induced sporophytes ofP. semipinnata, non-homologous chromosomes (58 univalents) were found during the meiotic process in sporocytes. InP. dispar, however, the meiotic cells showed many bivalent chromosomes (maximum 29ll). These results suggest thatP. semipinnata is allotetraploid, whereasP. dispar is autotetraploid.     

Paulownia taiwaniana,a hybrid betweenP. fortunei andP. kawakamii (Scrophulariaceae)

Paulownia taiwaniana, the widely cultivated, commercially important tree, has been suspected of being of hybrid origin at least since its original publication in 1975. Evidence in support of this thesis, derived from a number of different investigations, is presented in this paper.—Strong evidence comes from a controlled pollination study of the two supposed parental species,P. kawakamii andP. fortunei. F₁ seedlings, derived from reciprocal crosses between the suspected parents, exhibited identical banding patterns for a number of enzymes (such as SKDH, GOT, and IDH) withP. taiwaniana, when separated by electrophoresis. Furthermore, comparative morphological studies of trichomes and wood parenchyma patterns between the purported parents andP. taiwaniana reveal that this latter qualitatively exhibits characteristics that combine features of both of the suspected parental types. Biochemically, eight enzyme systems were compared in the three species here under discussion, and, without exception, the electrophoretic banding patterns exhibited byP. taiwaniana represented a combination of the alleles of the other two species. Perhaps the most convincing evidence comes from a genetic analysis of the progeny obtained by selfingP. taiwaniana. Genotypic segregation of the offspring based on a single locus each of SKDH and PGI fit the 1:2:1 hypothesis. Genotypic segregation of the offspring based on two loci each of SP and GOT fit the ratio of 3:6:3:1:2:1. This, taken in conjunction with the other data presented, clearly suggests thatP. taiwaniana is a hybrid involvingP. kawakamii andP. fortunei.     

Genetic variability in two hydrophilous species ofPotamogeton,P. pectinatus andP. filiformis (Potamogetonaceae)

Genetic variability inPotamogeton pectinatus andP. filiformis was studied by means of isozymes. The overall levels of variability were similar to some other well studied hydrophilous species, and were shown to be distributed more between than within populations. This partitioning of variability was attributed to three main factors. (1) Clonal growth (as measured by the frequency of multi-enzyme phenotypes) was shown to be a major factor in both species, although more important inP. pectinatus. (2) Low levels of sexual reproduction were shown to be a likely contributor to the partitioning of variability inP. pectinatus; such reproduction is probably limited by seedling recruitment rather than by infrequent flowering. (3) Geographical isolation was indicated as a factor regulating gene flow at distances of more than about 1000 km in both species, with the data suggesting that dispersal between populations is mainly by seed rather than by vegetative means.     

Apomixis in plants: structural and functional aspects of diplospory inPoa nemoralis andP. palustris

Summary Data on structural and functional aspects of mitotic diplospory and later stages of apomictic seed formation are reported forPoa palustris andP. nemoralis. In this study, the plant material of two Russian populations ofP. nemoralis andP. palustris were used for transmission electron microscope observations. Seed formation was investigated by phase contrast microscopy in two populations ofP. nemoralis collected in The Netherlands. The processes of transformation of the megasporocytes to the megaspore mother cells of diplosporous embryo sacs, and thereafter to one- and two-nucleate diplosporous embryo sacs (Antennaria type) were characterized by an increase of cell size, structural and functional reorganization of the nucleus, nucleolus, and cytoplasm, and cell isolation as a result of thickening of the cell wall. These were accompanied by an increase in the cell metabolic activity inferred from visual evidence of the activation of nucleus, nucleolus, endoplasmic reticulum, dictyosomes, mitochondria, and from the appearance of a dense population of ribosomes and polysomes. The diplosporous embryo sac of the Antennaria type was characteristic for bothP. nemoralis andP. palustris. No signs of the presence of synaptonemal complexes were observed during the process of diplosporous-embryo-sac megaspore mother cell differentiation and division. About 90–95% of the diploid egg cells of diplosporous embryo sacs were able to produce apomictic embryos. These embryos developed before anthesis. However, many of them degenerated at the globular stage because of lack of endosperm. The ultrastructural events occurring during the process of diplospory of apomictic species, and meiosis and megagametogenesis of sexually reproduced plants are discussed.Abbreviations DMC megaspore mother cell of diplosporous embryo sac - TEM transmission electron microscopy - ER endoplasmic reticulum     

Relationships betweenParacaryum intermedium andP. boissieri on Sinai,and the generic separation ofParacaryum andMattiastrum (Boraginaceae)

Paracaryum intermedium andP. boissieri differ only in their inflexed or flattened fruit wings, and often occur in mixed populations on Mt. Katherina, Sinai. This and cultivation experiments suggest that they may represent forms of a single species only. The fruit characters mentioned therefore are hardly useful for a generic separation ofParacaryum andMattiastrum.     

Investigations into the exploitation of heterogeneous soils by Lupinus albus L. and L. pilosus Murr. and the effect upon plant growth

In calcareous soils, genotypes of Lupinus albus L. generally grow poorly, resulting in stunted plants that often develop lime-induced chlorosis. In contrast, some genotypes of L. pilosus Murr. occur naturally in calcareous soils without developing any visible symptoms of stress. Some genotypic variation for tolerance to calcareous soil does exist in L. albus and the tolerance mechanisms need to be determined. The adaptation through root system morphological plasticity of L. albus and L. pilosus, to heterogeneous limed soil profiles (pH 7.8) containing either patches of acid (non-limed) soil, or vertically split between acid and limed soil, was investigated. When grown in the presence of patches of acid soil, L. albus had a 52% greater shoot dry weight and visibly greener leaves compared with plants grown in the homogeneous limed soil. Total root dry matter in the acid-soil patches was greater than in the control limed-soil patches. This was due to a four-fold increase in the cluster root mass, accounting for 95% of the root dry matter in the acid-soil patch. Although these cluster roots secreted no more citric acid per unit mass than those in the limed soil did, their greater mass resulted in a higher citrate concentration in the surrounding soil. L. pilosus responded to the patches of acid soil in a manner comparable with L. albus. When grown in the homogeneous limed soil, L. pilosus had a greater maximum net CO₂ assimilation rate (P_max) than L. albus, however, the P_max of both species increased after they had accessed a patch of acid soil. Differences were apparent between the L. albus genotypes grown in soil profiles split vertically into limed and acid soil. A genotype by soil interaction occurred in the partitioning between soils of the cluster roots. The genotype La 674 was comparable with L. pilosus and produced over 11% of its cluster roots in the limed soil, whereas the other genotypes produced only 1–3% of their cluster roots in the limed soil. These results indicate L. pilosus is better adapted to the limed soil than L. albus, but that both species respond to a heterogeneous soil by producing mainly cluster roots in an acid-soil patch. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrification and seasonal changes in bacterial populations in the rhizosphere ofSuaeda andArthrocnemum species growing in saline soils

Summary The nitrification rate in the rhizosphere of Suaeda and Arthrocnemum plants growing in saline soils, as affected by microbial populations, temperature, pH, and organic matter, was examined in the field throughout the year. The genera Nitrosomonas and Nitrobacter were most common in the rhizosphere soil. The bacterial counts in the rhizosphere of both plants fluctuated during the study period, reaching peak values during February–March and in August. The nitrate concentration in the rhizosphere soil could be related with the observed increase in the numbers of ammonium-oxidizers and nitrite-oxidizers in the latter part of the study period. The pH of the rhizosphere soils did not have any influence on the nitrification rate at the values measured. The rhizosphere organic content varied between 1.8 and 4% (w/w), showing the continuous availability of organic matter in the soil. The seasonal changes in bacterial populations in the rhizospheres of both plants was described as the result of the combination of several factors.     

Paramecium calkinsi andP. putrinum (Ciliophora, Protista) harboring alpha-subgroup bacteria in the cytoplasm

Summary New intracellular bacteria were detected in the cytoplasm ofParamecium calkinsi andP. putrinum. Some of the bacteria were not evenly distributed in the cytoplasm of the host but were found in the center of the cell, eventually near the nuclei, but not in the cortex area, whereas another species was found in the cortex area. These peculiarities of intracellular bacteria localization in the host suggest that the conditions in various parts of the cytoplasm favor bacterial maintenance to different extent. Due to the results obtained by transmission electron microscopy and in situ hybridization using appropriate oligonucleotide probes, the bacteria, three or possibly four species, are Gram-negative and belong to the alpha-subgroup of proteobacteria. Bacteria from one stock ofP. calkinsi were found to be infectious for bacteria-free cells ofP. calkinsi andP. nephridiatum.     

Meiosis and fertility of interspecific hybrids betweenPhaseolus vulgaris L. andP. acutifolius A. Gray

Summary Meiosis and fertility of interspecific hybrids obtained from reciprocal crosses between Phaseolus vulgaris and P. acutifolius were examined. Bivalents as well as univalents were found at Metaphase I. The majority of the microsporocytes had four or more univalents and the average was 6.3 univalents per cell. The average number of lagging chromosomes at Anaphase I was 2.3 per cell and the most frequent chromosome distribution at late Anaphase I was 10–12. The lower than expected number of lagging chromosomes as compared with the number of univalents at Metaphase I suggests the possible occurrence of precocious separation of bivalents. The male fertility as measured by pollen stainability was 17%, however, the frequency of pollen germination in selfing was 3.5%. Upon selfing of the interspecific hybrids, no dividing embryos were found even though 7 and 26% of the ovules were fertilized at 12 hours and four days after pollination. In backcrosses to P. vulgaris (male), 6 and 20% of the ovules were fertilized and 0 and 4% of the ovules contained dividing embryos at the same sampling times. When P. acutifolius was the male parent, respective values were 8 and 31% for fertilization and 0 and 13% for ovules with dividing embryos. The frequencies of backcross embryos recovered at 14–26 days were in agreement with the frequencies of dividing embryos at four days. The ability to obtain backcross plantlets demonstrates the feasibility to further utilize interspecific hybrids for the improvement of P. vulgaris Technical paper No. 5311 of the Oregon Agricultural Experiment Station. Research was supported by the Oregon Agricultural Experiment Station, the Science and Education Administration of the U.S. Department of Agriculture under Grant 5901-0410-8-0028-0 from the Competitive Research Grants Office, the Research Council of Oregon State University (NIH Biomedical Research Support Grant RR 07079) and the Processor Research Council of Oregon, A.R. and C T.S. are respectively supported by an African Graduate Fellowship from the African-American Institute and a fellowship from the National Science Council of the Republic of China     

Chromosome analysis and DNA homology in threePicea species,P. mariana,P. rubens,andP. glauca (Pinaceae)

A detailed karyotype analysis was made on the somatic complement ofPicea rubens andP. glauca. B-chromosomes were observed in someP. glauca populations. The karyotypes are generally asymmetrical with most of the chromosomes having median to median-submedian centromeres.Picea glauca chromosomes 2, 3, 7, and 8 have secondary constriction on their short arm and chromosome 10 has a secondary constriction on the long arm. Chromosome 3 was the most easily identifiable, as it has two secondary constrictions located on the short arm. InP. rubens, all the chromosomes but chromosomes 8 and 9 have one to four distinctive secondary constrictions. In general, the diagrammatic comparisons show a high degree of similarity amongP. mariana, P. rubens, andP. glauca. GenomicP. mariana probe strongly hybridized to dots of genomic DNA fromP. rubens andP. glauca indicating that there is a high sequence homology among these three species. The synchronizing agent, hydroxyurea was used at different concentrations to enhance the mitotic index of cell suspensions derived from embryogenic cultures. Hydroxyurea at 1.25 mM increased significantly the mitotic index. An increase of hydroxyurea from 1.25 mM to 5 mM and 10 mM resulted in a steady decrease of mitotic index.     

Long-term changes in amphipod population dynamics in a temperate estuary following ecosystem restoration

The Mondego estuary (Portugal) has suffered severe ecological stress over the last two decades, as manifested in the replacement of seagrasses by opportunistic macroalgae, degradation of water quality and increased turbidity. A restoration plan was implemented in 1998, which aimed to reverse the eutrophication effects, and especially to restore the original natural seagrass (Zostera noltii) community. This article explores the long-term changes in Ampithoe valida and Melita palmata (Amphipoda) populations in response to eutrophication (with consequent seagrass loss and macroalgal proliferation) and to the subsequent restoration plan (with progressive seagrass recovery and macroalgal biomass decline). Until the early 1990s, high densities of A. valida and M. palmata were recorded in the Mondego estuary, especially during the occurrence of the macroalgal bloom and during all the periods in which green macroalgae were available. After the implementation of the restoration plan, species abundance, biomass and production levels decreased considerably due to the progressive decline of green macroalgae. This implied the virtual disappearance of the amphipod population, mainly A. valida. Distinct behaviours displayed by the two species could be related to different food strategies and habitat preferences. Ampithoe valida showed feeding preferences for ephemeral softer, filamentous or bladed algae (e.g. Ulva sp.) due to its high caloric content, using the Z. noltii bed only as a habitat for protection against predators or shelter from wave action. On the other hand, M. palmata did not suffer a strong decline in its population density, biomass and production, which may indicate that this species is probably not a primary consumer of green macroalgae and may readily shift to alternative ecological niches. Handling editor: P. Viaroli