Changes in growth of plaice Pleuronectes platessa L. and sole Solea solea (L.) in the North Sea

The changes in growth of plaice and sole between 1957 and 1988, as estimated from samples of the commercial fishery and pre-recruit surveys, were analysed in order to study possible density dependent effects. Indices of potentially competitive biomasses of plaice and sole, based on Lloyd's index of mean crowding, were estimated from the average spatial distribution of various age groups during the summer growing period and from the population age structure as estimated by virtual population analysis.Growth of all age groups of sole increased in the 1960s and was stable in the 1970s and 1980s. In plaice only age groups 1 to 3 showed a similar increase in the 1960s, whereas the growth of 1-year-old plaice tended to decrease in the 1980s. Growth did not show a negative correlation with mean crowding, except in age group 1 of plaice and in age group 3+ of sole. It is concluded that these negative correlations do not provide unequivocal evidence for density dependent growth in plaice and sole, since they could equally well be caused by parallel but unrelated trends in time of one or more other factors. The simultaneous increase in growth in the 1960s of age groups of sole and plaice in the southern North Sea, and the absence of such an increase in age groups in the central North Sea, suggests that food availability must have increased in the Southern North Sea. This inference is supported by several macrobenthos studies. Whether the reduced growth of 1-group plaice in the 1980s, when recruitment was well above the average level, is caused by density dependent growth or to a reduced food availability remains an open question.     

Variations in settlement and growth of 0-group plaice (Pleuronectes platessa L.) in the dutch wadden sea as determined by otolith microstructure analysis

Larval growth, date of settlement, and subsequent growth of 0-group plaice were compared in the eastern (Dollard) and western (Texel) parts of the Dutch Wadden Sea in autumn 1988. Daily increment analysis in otoliths with SEM showed that specimens sampled in the Texel region, and at 2 Dollard stations, hatched early in the season, had a shorter larval period (50 to 61 d) with high growth rates, and early settlement. All specimens caught at the other 6 stations hatched later, had a long larval phase (62 to 82 d) and settled later in the season.Estimates of maximum growth based on optimal feeding conditions and the prevailing water temperatures in both tidal basins were compared to the growth rates observed in the field. According to previous studies, plaice in the Texel region have optimal growth. All late settlers in the Dollard and part of the early settlers also had optimal growth. However, some early settlers in the Dollard had significantly lower growth rates than the batch of synchronously settled specimens from the Texel region.     

Mortality rates of 0-group plaice (Pleuronectes platessa L.), dab (Limanda limanda L.) and turbot (Scophthalmus maximus L.) in European waters: I. Statistical analysis of the data and estimation of parameters

The early demersal phase of those species of flatfish with inshore nursery areas are usually accessible with relatively modest demands on gear and logistics. However, the design of the sampling programme, adjustment for gear efficiency, and statistical analysis of the resulting catch data, raise a number of questions which have not hitherto been addressed comprehensively.This paper presents a systematic analysis of all the published data known to us of demersal 0-group flatfish in nursery grounds adjacent to the North Sea and British coastal waters, together with some hitherto unpublished data. The analysis showed that in most cases catches from repeated tows of a beam trawl can be averaged, after appropriate correction for gear efficiency, to give representative estimates of fish density for a succession of sampling dates.From the time series of density estimates thus obtained a selection of the period from maximum density until the early part of the following year proved to give a consistent window for the estimation of mortality rates by use of regression methods. A total of 57 data sets was analysed (45 plaice, 11 dab and 1 turbot). Of these 48 gave essentially linear log/time trends, of which 7 showed some degree of curvature, (4 concave upwards and 3 concave downwards). In one further case the trend remained essentially horizontal (flat-topped) until near the end of the sampling window and then declined sharply. The remaining 8 trends were so erratic as to preclude any further conclusions to be drawn. There was no obvious regularity in the occurrence of either the concave or flat-topped patterns by location or in time.Estimates of density and mortality rate are presented, together with estimates of standard errors of these estimates. The interpretation of these estimates in relation to the design and frequency of the sampling procedure is discussed, with special reference to the different topographies of the areas surveyed.     

Distribution of flatfish eggs in the 1989 egg surveys in the southeastern North Sea,and mortality of plaice and sole eggs

From January to July 1989 eight egg surveys were carried out in the southeastern North Sea. The first three surveys were designed to estimate the egg production of plaice (Pleuronectes platessa) and cod (Gadus morhua). The other five surveys were aimed at the eggs of sole (Solea solea) and horse mackerel (Trachurus trachurus) Of a selection of the samples collected in 1989 all fish eggs were identified to species. This paper presents data on the distribution, timing and intensity of spawning of the flatfish species plaice, flounder (Platichthys flesus), dab (Limanda limanda), long rough dab (Hippoglossoides platessoides), sole, solenette (Buglossidium luteum), turbot (Scophthalmus maximus) and scaldfish (Arnoglossus laterna).Egg mortality was studied in plaice and sole and compared to previous estimates. Plaice egg mortality in 1988 and 1989 was higher than in 1987, coinciding with higher ambient temperatures. Egg production in sole was recorded earlier in the year in 1988 to 1990 than in 1984, and at lower ambient temperatures. Sole egg mortality rates were shown to be lower in 1988 to 1990 than in 1984.     

On selective tidal transport in the migration of North Sea Plaice (pleuronectes platessa) and other flatfish species

Evidence is given for selective tidal transport in North Sea plaice and other flatfish species. Data collected during midwater plankton surveys in two Dutch Wadden Sea inlets in early spring in the years 1970 to 1977 show that plaice, sole, flounder and dab demonstrate pelagic swimming behaviour in that period. Plaice, sole and flounder show a clear selective tidal transport mechanism to re-enter the Wadden Sea after staying in the open sea in winter whereas dab tends to leave the Wadden Sea. Data on by-catches of semi-pelagic pair trawl fishery for gadoids in the Dutch coastal area show that small quantities of plaice may be caught off the bottom throughout the whole year whereas sole moves to higher levels in two distinct periods only. The first period lower left diagram) demonstrate a strong preference for northgoing currents. This is also the direction towards the areas from which the plaice used had been transported to the laboratory and therefore this preference for northgoing tides might be interpreted as a clear case of homing to the Silverpits and Borkum areas.Also the rate of dispersion of the cluster of displaced tagged plaice in general (Fig. 18, lower right diagram) is much faster in the first months after release than that of the local plaice. Thus displaced plaice are more strongly motivated to migrate than non-displaced fish. This may well have been the case too in the plaice equiped with the transponding acoustic tags. This together with the release in an area with strong currents and narrow tidal ellipses means that the plaice should be considered to have been in an exceptional situation, extremely suited for travelling at great speeds in a fixed direction. Fig. 18 also shows the average surface tidal current velocities, derived from the 13 maps with hourly data on water circulation in the Stroomatlas Nederland (1963). It is obvious that the Lowestoft plaice, mostly released nearer to the coast within the release area, encountered the highest average current velocities observed in the North Sea. It cannot be proven that these circumstances explain completely the vast speed of the Lowestoft plaice but it certainly demonstrates that there is a bias in these experiments which could easily affect the results. When drawing conclusions in respect to the “normal” picture of plaice migration this bias should not be ignored.In the common sole selective tidal transport is observed in juveniles when entering the Wadden Sea in spring. In adult soles this mechanism is a common feature in March to May during the spawning migration but no evidence for the use of this mechanism is available during other periods of the year. The sole thus is an example of a flatfish species using selective tidal transport in a restricted period and for special purposes only.In plaice the use of selective tidal transport in the Wadden Sea inlets has been shown for juveniles. In adult plaice the need for using the mechanism might be much less although plaice have been seen swimming at the surface in spring (van den Ende, 1849) during day time quite in contrast with their normal behaviour. In spring nights, among soles swimming at the surface, plaice too have been observed (together with some dabs and turbots) but in much lower numbers than the sole (de Veen, 1967).On the whole there is not much evidence for a strong continuous use of selective tidal migration in plaice. No serious drops in the catch rates during specific tidal phases in the bottom trawl fisheries have been recorded by the results of the UK 81 otter trawl fishery. The coincides with the re-entering of soles in the Wadden Sea and with the well-known phenomenon of soles swimming at the surface. During this period the soles use selective tidal transport to reach the spawning grounds near the continental coasts.Data on catch per unit effort of a Dutch ottertrawler in 1958 to 1960, constantly fishing in one restricted area near Terschellingerbank lightvessel, reveal significant differences between day and night catch rates and a change from a preference for flood tide in the first half of the year to a preference for ebb tide in the second half.The available evidence for selective tidal transport in plaice is discussed in relation to the patterns of migration in 4 plaice sub-stocks studied by means of tagging experiments, and in relation to results of displacement experiments with mature and immature plaice. The tagging and displacement experiments present a picture of migration in which the directional swimming is a weak component superimposed on largely random movements and the speeds of travelling are low. The plaice react to displacement by trying to return to their original grounds and this tendency to home lasts for a full year.This picture about selective tidal transport contrasts with results obtained by the Lowestoft Laboratory. Plaice equiped with transponding acoustic tags did show largely directed and fast tidal migration before and after spawning. Arguments are given that these plaice were, however, in an exceptional position and may have shown homing behaviour. Notwithstanding this reservation to the Lowestoft experiments, these results and the present ones are explained if it is assumed that apparently only a fraction of the population uses the mechanism of selective tidal migration, thus saving energy and achieving quick transport when necessary. It is likely that in plaice as in sole the mechanism will be used in special cases only, probably for short periods, in certain areas.     

The role of nickel on somatic embryogenesis in Setaria italica L. in vitro

Nickel (0.13, 0.25, 0.5, 1.0 and 1.5 mg/l) increased the efficiency of somatic embryogenesis in leaf base and mesocotyl derived calli of Setaria italica. A lower concentration of nickel in the culture media promoted long-term maintenance of embryogenic calli that regenerated into plantlets. The plants obtained from embryogenic calli grown on Ni-containing medium showed tolerance to nickel. The growth of embryogenic callus was the maximum at 1.5 mg/l as compared to a lower or a higher concentration of Ni. Use of nickel may help in the induction of high frequency somatic embryogenesis in Setaria italica. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessment of genetic and phenotypic variation among intraspecific somatic hybrids of potato, Solanum tuberosum L.

Intraspecific somatic hybrids have been produced by protoplast fusion in eight combinations involving 10 dihaploids (2n= 2x= 24) in an attempt to provide new material for potato breeding. Cytological analysis revealed extensive variation in chromosome number, such as aneuploid, aneusomatic and mixoploid hybrids. Most of the hybrids represented the expected chromosome number of 48; however, the frequency of aneuploids reached 50% in some combinations. Some hybrids carried structurally rearranged chromosomes and exhibited a high frequency of aberrant anaphases. Isozyme and random amplified polymorphic DNA (RAPD) patterns of the hybrids from the same fusion combination were uniform. In the field, somatic hybrids showed wide phenotypic variation in 20 morphological characters. There was a significant correlation between certain leaf characters and the ploidy level, which may be used to distinguish the tetraploid hybrids from hexaploids and octoploids. Tuber yield and flowering intensity were highest in tetraploid hybrids (2n= 4x= 48). Eighteen of the 73 hybrids reached higher yields than the standard variety ‘Adretta’. Floral development and fertility were restored in hybrids derived from fusions between non-flowering or sterile dihaploids.     

Seasonal differences in concentrations of particulate lipids,proteins and chitin in the North Sea

The concentrations of particulate lipids, proteins and chitin were determined in the North Sea in January 1992, October 1992 and March 1993, with additional measurements of total suspended matter concentrations and organic matter contents in the suspended matter (POC) by ashing and wet-oxidation. During each of the three cruises, the proteins were by far the most important of the three components measured, followed by the lipids. The concentrations of chitin were always very low. The concentrations of these three components were highest in March and lowest in January; there was also a variation in the distribution over the North Sea between the three cruises. In January 1992, the suspended matter contained more organic matter in the northern North Sea than in the southern North Sea, but the higher concentrations of total suspended matter in the southern North Sea resulted in an inverse distribution for the concentrations of organic matter per volume of water. In March 1993, highest concentrations of the three organic compounds were observed in the Skagerrak and along the eastern side of the North Sea, decreasing towards the west. The suspended matter was richest in organic compounds in the Skagerrak and in the Norwegian Channel. In October 1992, the situation was very similar to that observed in January 1992, but the concentrations of organic compounds in the suspended matter and per volume of water were higher. The ratio of proteins to lipids was similar to this ratio in phytoplankton. The composition of the particulate organic matter became very close to that of phytoplankton if we assume that we missed a large amount of carbohydrates; the small differences persisting were probably due to the contributions of zooplankton, bacteria and terrestrial sources. The total contents of particulate lipids + proteins + chitin were low, but when estimated amounts of carbohydrates were added, the total particulate organic-matter concentrations found were very similar to the total particulate organic carbon concentrations found by wet-oxidation. During the period of sampling, no large concentrations of phytoplankton occured.     

Analysis of chromosome, mtDNA and cpDNA patterns in five somatic hybrids between Brassica alboglabra Bailey and Brassica campestris L.

Summary Somatic hybrids between Brassica alboglabra (CC) and B. campestris (AA) were produced through protoplast fusion. Hybrids of this combination have already been produced through sexual crosses and among other traits in the offspring, a CMS of ogura type was discovered. The reason for generating somatic hybrids was to create new nuclear-cytoplasmic combinations and/or cytoplasmic variants, which could be exploited in combination with the sexual hybrids. Mitosis and meiosis were studied and all hybrids were found to be of the AACCCC genomic constitution. The fusion of somatic cells resulted in altered cytoplasmic genomes.     

The influence of auxin type on the array of somaclonal variants generated from somatic embryogenesis of eggplant, Solanum melongena L.

Somaclonal variation is a possible source of variation in plant breeding. To apply this approach to eggplant breeding, somaclonal variations were observed among plants regenerated through somatic embryogenesis induced by 1-naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Variations including leaf shape, plant height, flower number per cluster, fruit shape, anther number per flower and pollen fertility were compared among ? 300 plants (R₀). Although these variations were confirmed among plants regenerated using both auxins, the frequencies of somaclonal variations in leaf shape, plant height, fruit shape and pollen fertility in the NAA experiment were higher than those in the 2,4-D experiment. Variations in flower number and anther number were also confirmed among plants from both experiments, although no significant differences in their frequency were observed. Subsequently, the inheritance of variations (leaf shape, fruit shape, and flower number) observed in R₀ was investigated from generation to generation (R₁). Variations in leaf shape and fruit shape were inherited while those in flower number were not. From these results we concluded that, although a high frequency of somaclonal variations were observed among plants from both methods, embryogenesis with NAA was more efficient than 2,4-D in eggplant.     

The progamic phase in Cichorium intybus L. Pollen tube growth in the style,incompatibility reaction and gametophytic competition

Summary Pollen germination and tube growth were studied following compatible, incompatible and pseudo-compatible pollinations in chicory. Pollen germination begins 3 minutes after compatible pollinations. The earliest pollen tubes reach the ovary 17 minutes later. Many of the later germinating pollen tubes are arrested and burst at the stigma papillae. In the transmitting tissue inhibitional effects due to negative interactions between pollen tubes are frequently observed. Complete self-incompatibility results in total inhibition of germination. In case of pseudo-self-compatibility, some pollen germinate but germination and stigma penetration are delayed and often result in pollen bursting. There is no self-incompatibility reaction in the transmitting tract but if the pollen tubes reaching this tissue are relatively numerous, negative interactions between them occur as after compatible pollinations. An hypothesis is presented which attributes the negative interactions between pollen tubes to the diffusion of a substance from the growing pollen tubes. This substance would also provoke pollen bursting on the stigma.     

Interspecific hybridization in Cucumis L. II. The crossability of species,an investigation of in vivo pollen tube growth and seed set

Summary The crossability of 12 Cucumis species of African and Asiatic origin was studied in a diallel cross, in order to find ways to realise the cross between the common cucumber (C. sativus L.) and its wild relatives which carry resistances against diseases and pests.Self-pollinations and cross-pollinations within species gave normal pollen tube growth and seet set. The different accessions within a species, as a rule reacted alike in interspecific crosses. In crosses between African species different crossing patterns were found, viz. bilateral congruity, bilateral incongruity and unilateral incongruity. Within C. sativus all accessions intercrossed freely, except one, which displayed unilateral incongruity.Good seed was harvested from several crosses and in some cases embryo culture was needed for further development of seeds. No good seeds were obtained from any cross between a species of the African group and C. sativus L.     

气象条件对海南省红厚壳生长的影响

分析研究了红厚壳生长与气象条件的关系。通过简单相关及逐步回归分析,建立了红厚壳的围径、株高生长量与气象条件间的数学模拟模型,结合红厚壳叶片的生长情况,得出了红厚壳生长适宜的气象条件指标。研究发现最适宜红厚壳生长的条件是：月平均气温25℃以上,最低气温18℃以上,降水量160mm以上,地表温度低于33℃,蒸发量在200mm以下。当最低气温小于10℃,降水量低于50mm时,红厚壳出现不抽芽的现象。     

Study of the variation in the somatic embryogenesis ability of some pea lines (Pisum sativum L. and Pisum arvense L.)

Summary Thirty lines of pea were tested in vitro to evaluate their ability to produce somatic embryos. Three distinct genotypic classes were detected (strong, medium and weak). The best responses were obtained in Pisum sativum. Abnormal somatic embryos and secondary embryogenesis seem to constitute the principal obstacle to the development of these structures.     

Identification of some Populus deltoides Marsh. x P. nigra L. clones,developed in North America,with the aid of allozymes

Summary Horizontal starch gel electrophoresis was done to assay 10 enzyme systems in root tips of 14 Populus deltoides x P. nigra clones developed by controlled hybridization and selected in North America, and some clones sharing one or both parents. The genotypes of the clones were determined for 31 loci coding for 10 enzyme systems. The interclonal allozyme variability was controlled by 12 loci. Each of the 14 clones had unique 12-locus genotypes, thus could be distinguished from each other. The clones differed from each other on an average of 4.2 loci. The first two Principal Components from Principal Component Analysis of the clonal allozyme genotype data accounted for 48% of the total variation in the 12 variant loci. 6-Pgd-3, Per-2, 6-Pgd-1, Aco-1 and Per-1 were found to be the most discriminating loci for the clones. The ordination of the clones on Principal Component axes 1 and 2 was in general agreement with the origin of the clones.     

Genetic impacts of fiber sugar content on fiber characters in Sea Island cotton, Gossypium barbadense L.

A genetic model with additive effect, dominant effect, additive × additive effect, and their interaction with environment effect (GE) was employed to analyze the 2-year data of F₁ and F₂ hybrids from 5 × 4 diallel cross, whose parents were Sea Island cotton with different fruit branch types. Unconditional and conditional genetic variances were analyzed to demonstrate genetic impacts of fiber sugar content on fiber characters. Results of unconditional genetic variances showed that dominance × environment interaction effect and additive × additive epistatic effects mainly controlled the genetic variation of fiber sugar content, and environment influenced the inheritance of fiber sugar content. Fiber uniformity, fiber elongation, and fiber micronaire were mainly controlled by dominance × environment effects. Fiber strength was mainly controlled by the interaction of additive × additive epistatic effects and the environment. Analysis of correlation coefficients indicated that the varieties or hybrids with high-fiber sugar content had short fiber, low-fiber uniformity, strength, and fineness, which indicated the close co-variation between fiber quality traits and fiber sugar content. Relatively better fiber quality traits could be obtained effectively through selecting parents with low-fiber sugar. Fiber sugar content of different parents had different genetic effect on fiber quality traits.     

Enhanced somatic embryogenesis,plant regeneration and total phenolic content estimation in Lycium barbarum L.: a highly nutritive and medicinal plant

Journal of Crop Science and Biotechnology - Lycium barbarum (Solanaceae), commonly known as Goji (or wolfberry), is popular for its nutritive and medicinal properties and is called a “super...     

Matromorphy in Brassica oleracea L. III. The influence of temperature,delayed prickle pollination and growth regulators on the number of matromorphic seeds formed

Summary Research was carried out into influence of extraneous factors on the frequency of matromorphic seeds. Because of a low seed set in different parental combinations, few significant differences were found. It appeared, however, that temperature could positively influence the frequency of matromorphic and hybrid seeds. Delayed prickle pollination and application of GA3 also increased the number of seeds.