Influence of lodging and nitrogen rate on the yield and yield attributes of oilseed rape (Brassica napus L.)

The effects of lodging and nitrogen rate were studied in a field trial of oilseed rapeBrassica napus L. Lodging decreased seed yield (16%) compared with a frame-raised crop. Yield decreased because of a significant reduction in each of the yield components coupled with a reduced plant population caused by stem breakage at the ground level. Lodging also reduced the final crop dry weight and harvest index. Seed yield was also lower when 200 kg ha^–1 nitrogen was applied than with 400 kg ha^–1. A general decrease in pod number m^–2, seed nuber pod^–1 and seed weight caused the lower yields. The use of 400 kg ha^–1 of nitrogen changed the contribution of the terminal raceme and individual branches with respect to seed yield. Seed nitrogn content and nitrogen yield increased at the 400 kg ha^–1, lowering both seed oil content and oil yield.     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

不同土壤水分状况下施硼对油菜硼吸收、利用的影响

1　引　　言我国是油菜生产大国 ,也是一个土壤缺Ｂ面积较大的国家 .由于油菜缺Ｂ问题突出 ,施用Ｂ肥已成为提高油菜产量、改善品质的重要措施[2 ,3 ,11] .但是 ,Ｂ肥的施用不但存在成本高、难度大、效率低的问题 ,而且也存在造成环境污染的可能性[9] .研究表明[8,10 ] ,不同油菜品种对缺Ｂ的反应存在基因型差异 ,因此 ,筛选、培育Ｂ营养高效基因型油菜以适应缺Ｂ土壤环境是解决油菜缺Ｂ问题的最有效途径之一 .植物对土壤中Ｂ的吸收、运输及利用因土壤水分状况而异[4 ,5] .研究不同水分条件下尤其是干旱情况下Ｂ素营养对油菜Ｂ营养效率的影…     

A model for the impact of herbicide tolerance on the performance of oilseed rape as a volunteer weed

The introduction of genetically modified, herbicide-tolerant, oilseed rape into the agricultural environment will have ramifications beyond weed control of the crop. Herbicide-tolerant rape will undoubtedly become part of established volunteer weed populations that occur in many cereal rotations, but its longevity in these populations and its impact as a weed and contaminant of future oilseed rape crops is uncertain. A life cycle model of volunteer oilseed rape was therefore constructed, incorporating existing information on physiological processes such as emergence pattern, longevity of buried seed, death rates of various structures and flowering and seeding as functions of density. The model was designed to allow interaction with control factors such as harvesting efficiency, herbicide treatment, ploughing and the sequence of crops in the rotation. Many of the physiological parameters (including seed decay rates, fecundity at high density) are uncertain, simply through lack of information in the appropriate context. Other parameters such as harvesting efficiency and herbicide kill rates, are inherently variable in farming. Accordingly, a Monte-Carlo approach, in which the model was run many times with different random realisations of parameter sets, was used to expose factors to which the seedbank was sensitive. Sets of 1250 realisations were compared for each of two extreme conditions: where herbicide could be used according to current intensive farming practice and where it was not an option (representing total herbicide tolerance). Modelled seedbank numbers after 5 yr ranged from 10^-3to 10⁴m^-2, realistic values found in arable soils. The use of herbicide, together with efficient harvesting of seed, clearly has an important suppressive effect on the oilseed rape seedbank, keeping it lower than 10²m^-2(a typical sowing rate) after 5 yr in more than 80% of realisations. In the absence of herbicide, seedbanks were invariably greater, but their absolute value depended strongly on harvesting efficiency and the extent to which high density of plants suppressed fecundity. Analysis of the time series from the simulations showed that the seedbank levels fluctuated by orders in magnitude from year to year in the absence of herbicide use. The sensitivity analysis of the life-cycle model led to the development of a simplified model for the seedbank dynamics. The model shows that the essential features of the dynamics result from an interaction between density-dependent fecundity and the perturbations due to management. Therefore predictions of the effect of herbicide tolerance on seedbank dynamics are highly uncertain without knowledge of the density dependence of fecundity. Furthermore, the sensitivity to management practices suggests that seedbank levels will be substantially more difficult to control if the efficacy of herbicide is compromised. It is concluded that the model and Monte-Carlo approach have many potential uses in exploring the effects of management, cultivar physiology and the nature of the transgenes.     

Coat protein-mediated resistance to Turnip mosaic virus in oilseed rape (Brassica napus)

Oilseed rape (Brassica napus) lines transformedwith the coat protein (CP) gene of Turnip mosaic virus(TuMV) were used to determine the effectiveness of resistance to TuMV mediatedby CP RNA or coat protein. Lines with one, two, or more copies of transgeneswere produced. T₂ and T₃ lines containing the CP genewitha functional start codon synthesised coat protein and showed high, but variablelevels of resistance to TuMV (21–96% resistant plants per line). TheT₁ and T₂ progeny of all lines carrying the CP gene withamutated start codon so that RNA but not protein was expressed, were assusceptible to TuMV as controls. Thus, in these experiments we were able toinduce CP-mediated resistance, but not RNA-mediated resistance.     

Expressing a gene encoding wheat oxalate oxidase enhances resistance to Sclerotinia sclerotiorum in oilseed rape (Brassica napus)

Sclerotinia sclerotiorum causes a highly destructive disease in oilseed rape (Brassica napus). Oxalic acid (OA) secreted by the pathogen is a key pathogenicity factor. Oxalate oxidase (OXO) can oxidize OA into CO₂ and H₂O₂. In this study, we show that transgenic oilseed rape (sixth generation lines) constitutively expressing wheat (Triticum aestivum) OXO displays considerably increased OXO activity and enhanced resistance to S. sclerotiorum (with up to 90.2 and 88.4% disease reductions compared with the untransformed parent line and a resistant control, respectively). Upon application of exogenous OA, the pH values in transgenic plants were maintained at levels slightly lower than 5.58 measured prior to OA treatment, whereas the pH values in untransformed plants decreased rapidly and were markedly lower than 5.63 measured prior to OA treatment. Following pathogen inoculation, H₂O₂ levels were higher in transgenic plants than in untransformed plants. These results indicate that the enhanced resistance of the OXO transgenic oilseed rape to Sclerotinia is probably mediated by OA detoxification. We believe that enhancing the OA metabolism of oilseed rape in this way will be an effective strategy for improving resistance to S. sclerotiorum. Xiangbai Dong and Ruiqin Ji contributed equally to this paper.     

Molecular markers for low-glucosinolate alleles in oilseed rape (Brassica napus L.)

Two recent studies have mapped QTLs associated with the level of seed glucosinolates in oilseed rape (Brassica napus L.). It was likely that the two most significant QTLs identified in each study were the same, as they were linked to RFLP alleles identified by common DNA probes. To investigate the utility of these probes in breeding programmes, they were used to study RFLPs in a range of low- and high-glucosinolate cultivars and breeding lines. It was shown that all low glucosinolate spring and winter cultivars possessed a specific RFLP fragment identified by probe wg3f7 which is linked to theGSL-1 QTL, and all high-glucosinolate cultivars possessed a specific RFLP fragment identified by probe wg7a8, which is linked to theGSL-2 QTL. Cultivar Ariana, which has intermediate levels of glucosinolates possessed the low-glucosinolate fragment atGSL-1 but the high-glucosinolate fragment atGSL-2. A similar result was found with the cvs. Martina and Bronowski which have intermediate and variable levels of glucosinolates. There were no other RFLP fragments identified by other DNA probes which were specific to either the low- or high-glucosinolate phenotypes. The use of probes wg3f7 and wg7a8 in selection of low-glucosinolate lines in breeding programmes is discussed.     

The effects of a paclobutrazol-based growth regulator on the yield, quality and ease of management of oilseed rape

A mixture of paclobutrazol and chlormequat chloride plant growth regulators (JF10405, Parlay C) was tested on field crops of two ‘double zero’ oilseed rape cultivars in two seasons. Application rate and timing of JF10405 were varied. Very large plots enabled the use of commercial farm equipment to treat and harvest the experiments. Untreated plots showed considerable lodging at harvest in all experiments. Treatment with JF10405 had only small effects on the height of mature plants but, generally, reduced lodging substantially even at the lowest rate tested. All JF10405 treatments increased seed yields, several significantly so, particularly a 2.50 litre/ha rate, although the optimum timing varied between experiments. Seed oil contents were little affected, but levels of glucosinolates were significantly decreased in some instances. Treatments giving good control of lodging also took less time to harvest, especially when cutting against the direction of the lodging. The results-are discussed in relation to the means by which these improvements in seed yield and quality were achieved, and crop management facilitated.     

Frequency and distance of pollen dispersal from transgenic oilseed rape (Brassica napus)

The objective of this study was to evaluate pollen dispersal inBrassica napus (oilseed rape). The selectable marker, used to follow pollen movement, was a dominant transgene (bar) conferring resistance to the herbicide glufosinate-ammonium. Transgenic and non-transgenic plants of the cultivar Westar were planted in a 1.1 ha field trial, with the transgenic plants in a 9 m diameter circle at the centre, surrounded by non-transgenic plants to a distance of at least 47 m in all directions. A 1 m circle of non-transgenic plants was sown in the centre of the transgenic area to allow estimation of the level of pollen dispersal when plants were in close contact. Honeybee hives were placed at the trial site to optimize the opportunity for cross-pollination. During the flowering period, regular observations were made of the number of plants flowering and the number and type of insects present in 60 1 m² areas. These areas were located uniformly around the plot at distances of 1, 3, 6, 12, 24, 36 and 47 m from the edge of the 9 m circle of transgenic plants. Seed samples were harvested from each of the 7 distances so that approximately 20% of the circumference of the plot was sampled at each distance. The centre non-transgenic circle was also sampled. Plants were grown from the seed samples and sprayed with glufosinate to estimate the frequency of pollen dispersal at each distance. In order to screen enough samples to detect low frequency cross-pollination events, seed samples were tested in the greenhouse and on a larger scale in the field. Results were confirmed by testing progeny for glufosinate resistance and by Southern blot analysis. The estimated percentage of pollen dispersal in the non-transgenic centre circle was 4.8%. The frequency was estimated to be 1.5% at a distance of 1 m and 0.4% at 3 m. The frequency decreased sharply to 0.02% at 12 m and was only 0.00033% at 47 m. No obvious directional effects were detected that could be ascribed to wind or insect activity.     

Persistence of oilseed rape (Brassica napus L.) outside of cultivated fields

It is widely assumed that most cultivated plants cannot persist in natural or semi-natural habitats. Most people thus assume that the plants growing outside of fields (in particular oilseed rape along roadsides) find their origins in the current or previous year’s cultivation of that crop. One consequence of this assumption is that the identity of plants growing on road verges is thought to reflect one of the cultivars currently or recently cultivated, while another consequence is the widespread belief that transgenic plants can be simply managed and controlled by stopping their cultivation. Our work shows that this assumption is false. We identify relict plants of a now unmarketable cultivar type of oilseed rape which have persisted in a semi-natural habitat (road verges) for at least 8 years according to farmer surveys in the studied area. More generally, we confirm that the dynamics of the feral oilseed rape plants of road verges is more complex than those resulting from spillage from agricultural machines or from neighbouring arable fields cultivated the previous year. Within the scope of transgenic oilseed rape cultivation, these results suggest that more studies on the dynamics of feral oilseed rape are needed in order to assess more precisely the risks of its invasiveness and its potential impact on genetic pollution between GM fields and non-GM fields. Received: 15 June 2000 / Accepted 31 July 2000     

Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse-grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2^oC to 20^oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2^oC or 5^oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15^oC or 20^oC), suggesting that the optimal incubation temperature was between 10^oC and 15^oC.     

Zinc efficiency of oilseed rape (t Brassica napus and t B. juncea) genotypes

Twenty five genotypes of oilseed rape (canola and mustard) were tested under varied supply of Zn (+Zn: 2 mg kg^–1 soil, -Zn: no Zn added) in two pot experiments in soil culture to determine the genotypic variation in tolerance to the Zn-deficient conditions, that is, to identify the Zn-efficient genotypes. On the basis of performance of genotypes in pot experiments, ten genotypes were tested in 1995 for their performance under varied supply of Zn (+Zn: 3.5 kg ha^–1, -Zn: no Zn added) on a Zn-deficient field in South Australia.Zn efficiency (ratio of shoot dry matter in -Zn to shoot dry matter in +Zn treatment and expressed in percentage) in pot Experiment 1 varied from 35% for 92-13 to 74% for Siren. Narendra, Dunkeld, Barossa, Oscar and Xinza 2 performed well under -Zn treatment. Zn efficiency in Experiment 2 varied from 32% for Wuyou 1 to 62% for Pusa Bold. Pusa Bold and CSIRO-1(mustard genotypes) were the most efficient in terms of dry matter production among all the oilseed rape genotypes tested. Root dry matter accumulation was significantly higher in Zn-efficient genotypes. Zn efficiency (ratio of seed yield in -Zn to seed yield in +Zn and expressed in percentage) in field experiment varied from 62% for Huashang 2 to 76% for Dunkeld. With few exceptions, the ranking of genotypes in pot and field experiments indicates similarity in their response to Zn deficiency. There looks to be genetic control over Zn concentration in tissues. Zn-efficient genotypes had lower Zn concentration in roots and higher Zn concentration in youngest fully opened leaf blades, indicating a better transport of Zn. This, together with a higher Zn uptake, appears to be the basis of expression of Zn efficiency.     

Opportunities for gene transfer from transgenic oilseed rape (Brassica napus) to related species

Before novel transgenic plant genotypes are grown outside containment facilities and evaluated under field conditions, it is necessary to complete a risk assessment to consider the possible consequences of that release. An important aspect of risk assessment is to consider the likelihood and consequences of the transgene being transferred by cross-pollination to related species, including other crops, weeds and ruderal populations. The purpose of this report is to review the literature to assess the ease with whichBrassica napus can hybridize with related species. The evidence for hybridization is considered at three levels: a) by open pollination, b) by hand pollination and c) by the use ofin vitro ovule and embryo rescue techniques; and also examines the fertility and vigour of the F₁, F₂ and backcross generations. Four species are reported to hybridize withB. napus by open pollination:B. rapa andB. juncea using fully fertile parents; andB. adpressa andR. raphanistrum using a male-sterileB. napus parent. Seventeen species are reported to form hybrids (including the four species above) withB. napus when pollination is carried out manually. At least 12 of these species were unable to form F₂ progeny, and eight were unable to produce progeny when the F₁ was backcrossed to one of the parental species. Many factors will influence the success of hybridization under field conditions, including: distance between the parents, synchrony of flowering, method of pollen spread, specific parental genotypes used, direction of the cross and the environmental conditions. Even where there is a possibility of hybridization betweenB. napus and a related species growing in the vicinity of a release, poor vigour and high sterility in the hybrids will generally mean that hybrids and their progeny will not survive in either an agricultural or natural habitat.     

Seed zinc content influences early vegetative growth and zinc uptake in oilseed rape (Brassica napus and Brassica juncea) genotypes on zinc-deficient soil

Low-Zn seed (around 80 ng Zn per seed) and high-Zn seed (around 160 ng Zn per seed) of Zhongyou 821 (a traditional Brassica napus genotype from China found to be Zn-inefficient in our previous experiments), Narendra (Zn-efficient B. napus genotype from Australia) and CSIRO-1 (a Zn-efficient B. juncea genotype from Australia) oilseed rape genotypes were sown in pots containing Zn-deficient siliceous sand fertilized with low Zn supply (0.05 mg Zn kg^–1 soil) or high Zn supply (2.0 mg Zn kg^–1 soil) in a controlled environment. After six weeks, plants derived from the high-Zn seed had better seedling vigour, increased root and shoot growth, more leaf area and chlorophyll concentration in fresh leaf, and higher Zn uptake in shoot compared to those from low-Zn seed at low Zn supply; the impact of high-Zn seed was more marked in Zhongyou 821 compared with CSIRO-1 and Narendra. The influence of high-Zn seed was dissipated at high Zn supply. CSIRO-1 was superior in terms of shoot dry matter production and Zn uptake in shoots at low Zn supply. The results demonstrate that although oilseed rape has very small seeds (about 3 mg per seed weight) compared with wheat (30 mg per seed weight), Zn reserves present in this very small seed still have a strong impact on early vegetative growth as well as on Zn uptake of plants in Zn-deficient soils. The results suggest that sowing high-Zn seed coupled with growing Zn-efficient genotypes may help in sustaining the production of oilseed rape in Zn-deficient soils, and this has implications for improved seed technology.     

Discovery and assay of single-nucleotide polymorphisms in barley (Hordeum vulgare)

The least ambiguous genetic markers are those based on completely characterized DNA sequence polymorphisms. Unfortunately, assaying allele states by allele sequencing is slow and cumbersome. The most desirable type of genetic marker would be unambiguous, inexpensive to assay and would be assayable singly or in parallel with hundreds of other markers (multiplexable). In this report we sequenced alleles at 54 barley (Hordeum vulgare ssp. vulgare) loci, 38 of which contained single-nucleotide polymorphisms (SNPs). Many of these 38 loci contained multiple polymorphisms, and a total of 112 polymorphisms were scored in five barley genotypes. The polymorphism data set was analyzed both by using the individual mutations as cladistic characters and by reducing data for each locus to haplotypes. We compared the informativeness of these two approaches by consensus tree construction and bootstrap analysis. Both approaches provided similar results. Since some of the loci sequenced contained insertion/deletion events and multiple point mutations, we thought that these multiple-mutated loci might represent old alleles that predated the divergence of barley from H. spontaneum. We evaluated sequences from a sample of H. spontaneum accessions from the Eastern Mediterranean, and observed similar alleles present in both cultivated barley and H. spontaneum, suggesting either multiple domestication events or multiple transfers of genes between barley and its wild ancestor.     

Effects of dalapon and TCA on the growth and yield of oilseed rape (Brassica napus)

The tolerance of oilseed rape (Brassica napus cv. Jet Neuf) to the herbicides dalapon and TCA was studied in two series of 10 experiments over four years. TCA (7.6–30.4 kg a.i./ha) was applied pre-emergence and dalapon (2.9–11.6 kg a.i./ha) was sprayed post-emergence between September and November at two growth stages (2–5, 4–7 leaves). Dalapon at all doses caused the leaves to appear yellow-green in colour and at the higher rates (5.8–11.6 kg a.i./ha), especially when applied at the later of the two growth stages, scorched the leaf margins and stunted the plants. TCA also caused the leaves to appear yellow-green and was noted to affect the retention of water by the leaf surfaces. In general the visible effects of treatment with dalapon were more severe than those of TCA. The effects of these two herbicides on rape seed yields were variable, with some trials showing statistically significant reductions and others none. However by combining the results of trials with similar treatments some underlying trends were identified. In the overall analyses dalapon at 11.6 kg a.i./ha, applied at both growth stages and at 5.8 kg a.i./ha, applied at the later one, reduced yields significantly. TCA at 15.2, 22.8 and 30.4 kg a.i./ha also caused significant yield reductions in the combined analyses. Further statistical analysis questioned the safety of the lower rates of both herbicides, which were similar to those recommended by the manufacturers. The severity of the foliar damage caused by dalapon was well correlated with the risk of significant yield reductions but not with the actual percentage loss of yield. No such correlations were possible with TCA as the visual symptoms were similar on all sites and were unaffected by dose. Recent changes in agricultural practices and in crop cultivar do not appear to have altered the sensitivity of rape to dalapon and TCA appreciably.     

Drought adaptability of Agrobacterium rhizogenes-induced roots in oilseed rape (Brassica napus var. oleifera)

Abstract. Soil grown oilseed rape ( Brassica napus L. var. oleifera M., cv. Darmor) seedlings at the cotyledon stage (one week old), were inoculated in vivo at the base of the hypocotyl with Agrobacterium rhizogenes harbouring the pRi 15834 plasmid. Resulting adventitious root formation was observable about 2 or 3 weeks after infection. Differential Ri-induced root emergence and subsequent development occurred depending on water conditions and closeness of the wounding site to the soil surface: either thin, hairy roots growing rapidly and plagiotropically at the soil level under humid atmosphere, or hairless and fleshy, slowly growing aerial roots developed. The hairy roots were highly drought susceptible, whereas aerial roots revealed some potential for drought tolerance. Unlike normal roots, none of these Ri-induced roots appeared able to give rise to drought rhizogenesis in plants subjected to progressive drought stress. However, under hardening, achieved through successive and moderate drought stress-rehydration cycles, both types of Ri-induced roots improved drought tolerance and could express the morphogenetic differentiation programme leading to the formation of short, tuberized, drought-adapted, roots. These results, discussed in terms of hormonal imbalance and drought tolerance regulation, suggest that the Ri T-DNA gene expression, responsible for adventitious root induction and growth behaviour, is further regulated through the host plant.     

Differential response of oilseed rape (Brassica napus L.) cultivars to low boron supply

Three experiments were carried out on an alluvial sandy loam (Udifluvent) at Tonglu, Zhejiang Province, P.R. China from 1992 to 1995, to determine the genotypic range in boron (B) efficiency of 16 oilseed rape (Brassica napus L.) cultivars, to identify the B-efficient cultivars and to identify specific responses which can be utilised for selection in a breeding program. The 16 cultivars which included high-quality and conventional types differed significantly in survival, plant height, leaf area, shoot dry weight and seed yield; however, the ranking of the cultivars for their seed yield or other plant traits differed with B treatment. With severe B deficiency (CaCl2 extractable B < 0.26 mg/kg) and no boron applied, none of the cultivars exhibited significant B efficiency, with seed yield <300 kg/ha. With moderate B deficiency (CaCl2 extractable B 0.34 mg/kg or 0.17 kg B/ha applied), seed yield varied significantly among the cultivars from 397 to 1889 kg/ha in year 1 and from 616 to 1260 kg/ha in year 3. Zhongyou 821 and 92-13 were the most B-efficient and Wanyou 324, Huashuang 2 and Su 2051 were the most B-inefficient cultivars under moderate B deficiency. Significant differences were found among the cultivars in leaf B concentration; however, there was no close relationship between leaf B concentration and seed yield responses to B of oilseed cultivars. Of all the growth parameters measured, leaf area was the early indicator best correlated with subsequent seed yield and may be useful for evaluating the response of cultivars to low B supply. Contrary to current opinion, it was also found that high-quality oilseed rape cultivars were not all sensitive to low B supply nor were all conventional cultivars B-efficient.     

Chloroplast-released inhibitor of phenylalanine ammonia-lyase from barley (Hordeum vulgare) seedlings

Isolated chloroplasts of barley seedlings ( Hordeum vulgare L.) when kept in light, released a soluble, thermostable factor that inhibited phenylalanine ammonia-lyase (PAL) in vitro . Highest inhibition was found when chloroplasts were suspended in PAL-containing extract and kept in light. Efficiency of PAL activity inhibition did not depend greatly on the type of medium used for chloroplast isolation, nor on the composition of buffer in which the enzymatic activity was measured. It is proposed that in green tissues chloroplasts may participate in regulation of cytoplasmic PAL activity.     

Effects of barley straw (Hordeum vulgare) on freshwater and brackish phytoplankton and cyanobacteria

A short-term laboratory study was conductedto investigate the effect of barley strawin controlling several common phytoplanktonand cyanobacterial species. Following aone-month incubation of barley straw incoarsely filtered fresh Potomac River andbrackish Patuxent River waters, the growthof six autotrophic taxa was followed inculture. Barley straw slurry reduced theyield of three taxa (Ankistrodesmusfalcatus, Chlorella capsulata, Isochrysis sp.) in comparison withcultures not receiving the slurry. Although no significant changes in growthwere detected with three other taxa (Cyclotella sp., Prorocentrumminimum, freshwater Pseudanabaenasp.), some patterns indicated potentialimpacts of the barley straw. First, ahigher addition of straw to Cyclotella sp. resulted in a lower biomassaccumulation than in cultures receivinglower levels. Second, the bloom-formingdinoflagellate Prorcentrum minimumwas apparently stimulated at low barleystraw levels, perhaps suggesting conditionsassociated with the straw(metals-chelation, bacterial-producednutrients) might stimulate dinoflagellategrowth. Third, species shifts wereobserved in two of the cultures, withbarley straw favoring shifts from Isochrysis to a Cyclotella sp. –Thalassiosira sp. mixture and shiftsfrom Pseudanabaena to a Pseudanabaena – Scenedesmus mixture. These results provide new records for thesusceptibility of freshwater and brackishphytoplankton taxa to barley strawexposure, including species-specificresponses and shifts in species dominancein mixed assemblages.