Effect of Rice Straw Incorporation on Phytotoxicity of Isoxaflutole to an Exotic Weed Phalaris minor Retz.

Phalaris minorRetz. is a major exotic annual weed in the wheat (Triticum aestivum L.) crop. Unharvested rice (Oryza sativa L.) straw, unburned and burned, is often incorporated in the field prior to cultivating wheat. Isoxaflutole (Balance), a pre-emergent systemic soil applied herbicide, has potential to control P. minor. Glasshouse experiments were conducted to determine the phytotoxicity of isoxaflutole defined by reductions in relation to shoot length of P. minor when grown in unamended soil or soil amended with unburned or burned rice straw. A 120 g soil was amended with 0, 1, 2 and 4 g of unburned or burned rice straw, and placed in 150 mL styrofoam pots. Appropriate amount of isoxaflutole (75% active ingredient, ai) was added to pots to get final concentration of 0, 7.5, 30, 60 and 120 μg ai/pot. Unamended soil and soil amended with unburned or burned rice straw were analyzed for pH and organic matter; two important determinants of isoxaflutole activity. Results indicate a significant reduction in shoot length of P. minor when grown in soil treated with isoxaflutole at 30, 60 or 120 μg ai/pot. Inhibition in the shoot length of P. minor was observed when soil amended with unburned straw was treated with isoxaflutole at 7.5 and 30 μg ai/pot compared with unamended soil treated with similar amounts of isoxaflutole. No significant change in isoxaflutole toxicity was observed when soil amended with unburned straw was treated with isoxaflutole at 60 and 120 lg ai/pot compared with unamended soil treated with similar amounts of isoxaflutole. Isoxaflutole phytotoxicity to P. minor shoot length was eliminated when soil amended with burned straw was treated with isoxaflutole at 7.5 and 30 μg ai/pot. P. minor shoot length was greater when soil amended with burned straw was treated with isoxaflutole at 60 and 120 μg ai/pot relative to herbicide-treated unamended soils. We conclude that incorporation of burned rice straw greatly reduces the phytotoxicity of isoxaflutole toP. minor.     

环境因子对奇异虉草和小子虉草种子萌发的影响

在室内条件下考察了环境因子温度、pH、盐分、土壤含水量以及种子埋深对外来入侵植物奇异虉草和小子虉草种子萌发和幼苗生长的影响,并与小麦进行对比研究.结果显示;(1)当温度为5℃、NaCl浓度为0.25 mol/L以及种子埋藏深度达到30 mm时,奇异虉草和小子虉草的种子完全不能萌发,而同等条件下小麦种子的发芽率分别依次为89.33%、53.33%和95.00%.(2)在pH 4.0～10.0和土壤含水量10.0%～25.0%条件下,奇异虉草和小子虉草的种子均能萌发;但pH在4.0和10.0以及土壤含水量低于15%时,其发芽率受到显著抑制;当土壤含水量为10%时奇异虉草和小子虉草的种子发芽率分别为19.33%和16.67%,而小麦种子的萌发完全受到抑制.(3)奇异虉草和小子虉草的幼苗最适生长环境为,温度25℃～30℃、pH为6.0～9.0、NaCl浓度0～0.05 mol/L以及种子埋藏深度为0～5 mm.研究表明温度、盐分和种子埋藏深度是影响奇异虉草和小子虉草种子萌发的关键因素,而偏碱性环境更有利于其种子萌发,其种子萌发对干旱胁迫的耐受性强于小麦.     

Understanding invasion as a process: the case of <Emphasis Type="Italic">Phalaris arundinacea</Emphasis> in wet prairies

Invasive plants that most threaten biodiversity are those that rapidly form a monospecific stand, like the clonal grass, Phalaris arundinacea. Understanding complex and potentially interacting factors that are common in urban and agricultural landscapes and underlie rapid invasions requires an experimental, factorial approach. We tested the effects of flooding and nutrient and sediment additions (3 × 3 × 3 = 27 treatments, plus a control with no additions) on invasion of Phalaris into mesocosms containing wet prairie vegetation. We discovered a three-step invasion and degradation process: (1) initially, resident native species declined with prolonged flooding and sediment additions, and (2) prolonged flooding, sedimentation, and nutrients accelerated Phalaris aboveground growth; biomass rose to 430 times that of the control within just two growing seasons. The dramatic expansion of Phalaris in the second year resulted in the formation of monospecific stands in over one-third of the treatments, as (3) native species continued their decline in year 2. Disturbances acted alone and in combination to make the resident wetland community more invasible and Phalaris more aggressive, leading to monospecific stands. Yet, Phalaris did not always “win”: under the least disturbed conditions, the resident plant canopy remained dense and vigorous and Phalaris remained small. When anthropogenic disturbances coincide with increases in the gross supply of resources, more tolerant, fast-growing, and morphologically plastic plants like Phalaris can invade very rapidly. The fluctuating resource hypothesis should thus be refined to consider the role of interacting disturbances in facilitating invasions.     

油菜类型和品种对外来入侵杂草小子虉草的替代控制作用

外来入侵植物小子虉草（Phalaris minor Retz.）是世界公认的冬季农田恶性杂草,掌握农作物对其替代控制作用具有重要的研究价值。前期研究表明,油菜是替代控制小子虉草的优良农作物,然而,目前尚不清楚油菜类型与品种对其控制能力的影响。为此选取与小子虉草同域发生的不同类型（白菜型油菜、芥菜型油菜和甘蓝型油菜）油菜品种各3种,通过田间小区实验和室内化感作用测定,对比研究其对小子虉草的生长、繁殖、表型以及化感作用的影响。田间实验显示：竞争方式（种内或种间竞争）和油菜类型对小子虉草的地上生物量、种子数、株高、分枝数、叶面积和比叶面积存在极显著（P=0.0001）影响;而油菜品种对小子虉草的地上生物量（P=0.6064）、种子数（P=0.3577）、株高（P=0.4279）、分枝数（P=0.6357）、叶面积（P=0.8839）和比叶面积（P=0.3424）均无显著影响。3种类型油菜对小子虉草生长、繁殖以及表型的影响存在明显差异,其中芥菜型油菜对小子虉草的上述指标的影响最强,而白菜型油菜的影响最弱。室内生物测定显示,油菜对小子虉草具有化感抑制作用,当供试油菜叶片水提液浓度为0.1 g/mL时,小子虉草种子的萌发和幼苗的株高、根长、生物量均被显著抑制;研究也表明不同类型油菜对小子虉草的化感作用显著不同,同等条件下,芥菜型油菜对小子虉草的化感抑制作用最强。综上所述,油菜类型对外来入侵小子虉草的控制作用存在显著差异,其中芥菜型油菜对植物小子虉草的替代控制作用明显优于白菜型油菜和甘蓝型油菜,而其强的化感抑草特性或许是其强控草能力的原因之一。另外,本研究也为进一步利用油菜替代控制入侵植物小子虉草提供了参考。     

Metabolic responses of Lemna minor to lead ions II. Induction of antioxidant enzymes in roots

Duckweed Lemna minor L. was grown on Wang culture medium supplemented with lead ions for 24 hours. Metal was tested at 1.5, 3 and 6 mg·dm⁻³ concentrations. The response of antioxidant enzymes, such as superoxide dismutase, catalase and peroxidase in lead-treated roots of duckweed was investigated. Lead ions had no effect on the spectrum of catalase and peroxidase isoenzymes while a new isoform of superoxide dismutase appeared on the Pb treated roots. A lead-depended increase in activities of superoxide dismutase and peroxidase was observed, whereas catalase activity was maintained at relatively constant values at lower lead concentrations and then decreased markedly below control level.     

Stigma proteins of the two loci self-incompatible grass Phalaris coerulescens

Summary Protein extracts from four self-incompatible genotypes of Phalaris coerulescens were subjected to analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and ultra-thin isoelectric focusing. A comparison between stigma, root and leaf extracts showed that there was no significant difference in electrophoretic or isoelectric focusing patterns between the genotypes for both root and leaf proteins. However, stigma protein patterns did vary between genotypes especially within the molecular weight region of 43 000–97 000 and within the pI range 5–7. The stigma-specific changes strongly suggest a link between the self-incompatible genotype and these stigma proteins. However, because there are two loci involved, it is not yet possible to precisely assign particular proteins to each S- or Z-allele.     

Phytotoxic activity of selected water-soluble metabolites of Fusarium against Lemna minor L. (Duckweed)

Phytotoxicity and inhibitory effects of the fusarial toxins fumonisin B₁ (FB₁) [m.p. 103–105 °C], fusaric acid [m.p. 106–107 °C], butenolide (4-acetamido-4-hydroxy-2-butenoic acid lactone) [116–117 °C], 9, 10-dihydroxyfusaric acid [m.p. 150–155 ° C], and moniliformin on chlorophyll synthesis in the aquatic macrophyte Lemna minor (duckweed) were examined. FB₁ proved to be most active, reducing the growth of L. minor fronds and their ability to synthesize chlorophyll by 53% and 59%, respectively, at 0.7 g/ml. The growth rate of L. minor was reduced 59% by 6.7 g/ml fusaric acid, 62% by 66.7 g/ml butenolide, and 22% by 66.7 g/ml 9,10-dihydroxyfusaric acid. Moniliformin was the least phytotoxic to L. minor, with only a 16% suppression of growth rate and a 54% reduction in chlorophyll at 66.7 g/ml.The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.     

Metabolic responses of Lemna minor to lead ions I. Growth, chlorophyll level and activity of fermentative enzymes

Duckweed Lemna minor L. was grown on Wang culture medium supplemented with lead ions for 24 hours. Metal was tested at 1.5, 3 and 6 mg·dm⁻³ concentrations. The growth of Lemna minor was inhibited by lead ions, but the dry to fresh weight ratio increased as the concentration of Pb²⁺ in the medium increased. With increased concentrations of Pb ions, the contents of chlorophyll a and chlorophyll b in roots and fronds were correspondingly lower in comparision with the control. The effect of lead upon activities of some glycolitic and fermentative enzymes in roots of duckweed was examined. The activity of pyruvate kinase decreased with increasing lead concentrations, but cytosolic malate dehydrogenase behaved in an opposite manner. The lowest concentration of Pb stimulated alcohol dehydrogenase; phosphoenolopyruvate carboxylase activity was maintained at relatively constant values at all tested lead concentrations.     

Genetic variation in photosynthetic characteristics among invasive and native populations of reed canarygrass (Phalaris arundinacea)

With the extensive spread of invasive species throughout North America and Europe there is an urgent need to better understand the morphological and physiological characteristics of successful invasive plants and the evolutionary mechanisms that allow introduced species to become invasive. Most ecological studies have focused on morphological differences and changes in community dynamics, and physiological studies have typically explored the differences between native and invasive species. In this study, 15 different genotypes of Phalaris arundinacea from both its native (European) and invasive (North American) range were grown in a common garden experiment to monitor the physiological differences between native and invasive genotypes. Here we present data that suggests high variability exists in the physiological traits among genotypes of P. arundinacea, yet genotypes from the native range are not necessarily physiologically inferior to the hybridized invasive genotypes. Previous work has shown that multiple introductions of P. arundinacea from various European locations to the United States resulted in numerous hybridization events, yielding more genetic variability and phenotypic plasticity in the invasive range. Of the genotypes studied, both morphological and physiological traits of genotypes with French origin were significantly different from the plants from the Czech Republic, North Carolina, and Vermont. The lack of clear differences between native and invasive genotypes indicates that physiological traits may be highly conserved in P. arundinacea and enhanced photosynthetic rates are not indicative of successful invasive genotypes. Instead, morphological traits and defensive secondary compound metabolism may play a more important role in the success of P. arundinacea within its invasive range, and patterns of genetic variation in physiological traits between invasive and native range may be more important than the mean traits of each region when explaining reed canarygrass’ invasive potential in North America.     

Calcium oxalate formation is a rapid and reversible process inLemna minor L.

Summary Lemna minor root tips form raphide Ca oxalate crystals in both the root cap and root proper. An in vivo system was developed to examine raphide crystal bundle formation in the root of intact plants. By increasing the exogenous Ca concentration, crystal bundle formation could be induced. Entire new crystal bundles could be formed within 30 minutes of an inductive stimulus. The process was reversible with recently formed crystal bundles being dissolved over a period of about 3 hours. Older, previously existing bundles were more resistant to dissolution. The calmodulin antagonists, chlorpromazine and trifluoperazine (300 M), prevented crystal formation and caused dissolution of some crystal bundles, even in the presence of exogenous Ca. When the antagonists were flushed out and replaced with fresh medium, crystals were formed in cells where dissolution had occurred under the influence of the antagonists. The Ca ionophore A 23187 (20 M) caused slow dissolution of crystal bundles, even in the presence of exogenous Ca. A model describing the control of and physiological significance of Ca oxalate formation in plants is presented and discussed with respect to the results obtained in this study.     

Effects of herbicide applications in wheat fields: Is phytohormones application a remedy?

The present review encompasses the physiological and yield constraints of herbicide applications with special reference to wheat productivity. Post-independence lagging of Indian agriculture to feed its population led to haphazard use of chemical pesticides and weedicides which deteriorated the productivity pay-off particularly of wheat and rice. Past some decades witnessed the potential use of certain phytohormones in augmenting abiotic stress to get rid of yield gap and productivity constraints. We summed up with reviewing the potential role of these natural regulators in overcoming above mentioned drawbacks to substitute or to integrate these chemicals with the use of plant hormones.     

Changes during development in the permeability of sclerotia ofSclerotinia minor to an apoplastic tracer

Summary Sclerotia ofSclerotinia minor produced in culture are permeable to the apoplastic tracer sulphorhodamine G (SR) in early stages of their development, but become impermeable as the rind differentiates at the onset of maturation. Reduction in permeability corresponds with deposition of the dark brown pigment in the rind cell walls rather than initiation of the rind as a distinct surface layer. Fluorochrome permeation into cut sclerotia indicates that, while the rind is the primary barrier, the walls and extracellular matrix of the cortex and medulla of mature sclerotia also impede SR movement. Some cells take up fluorochrome into the protoplast. This indicates enhanced proton pumping activity at the cell surface, which suppresses ionisation of the fluorochrome, allowing it to cross the plasma membrane and accumulate in the hyphae. In intact sclerotia such hyphae are very rare and were detected only at one stage of development. However, in cut sclerotia at the two earliest stages of development most of the hyphae near the cut surface accumulated SR and it is possible that this is due to proton pumping activity induced by wounding.Abbreviations ECM extracellular matrix - SR sulphorhodamine G     

The influence of some environmental factors on the production of Carex vesicaria and Phalaris arundinacea

The study deals with the annual cycles of biomass, productivity and necrosis of the perennial wetland species Carex vesicaria and Phalaris arundinacea, and with the main growth parameters during the first part of 1979. The amplitudes of biomass variation differ, but other features of the development are largely the same. To detect the various climatic factors which determine the above-ground biomass dynamics, a procedure of multiple stepwise regression has been used. Regressions for annual trend and variation in production were obtained. They provide coarse models, which may be improved by including translocation to belowground organs.Nomenclature follows P. Fournier (1977): Les quatres flores de France. Paris.     

Identification of Naemacyclus minor hyphae within needle tissues of Pinus sylvestris by immunoelectron microscopy

Cultural investigations revealed that Naemacyclus minor, Lophodermium seditiosum and Cenangium ferruginosum were the most frequent colonizers of asymptomatic and symptomatic Pinus sylvestris needles. Since ultrastructural observations showed that morphological features were not suitable to differentiate hyphae of N. minor from hyphae of other isolates, the on-section immunogold labelling technique was applied in combination with an anti-N. minor specific immunoserum. The specificity of this serum was tested against culture hyphae of all isolates. Anti-N. minor specific immunoserum was then used to identify N. minor hyphae in thin sections of green P. sylvestris needles. The infection loci identified were restricted to small tissue areas located in the vicinity of stomata. In the hypodermis, hyphae and endocell-containing hyphae were located within the lumina of host cells but outside the protoplast. The growth of hyphae from cell to cell occurred through pits. The hyphae spreat into the mesophyll intercellularly and continued with the intracellular colonization of moribund and dead mesophyll cells in a later stage of infection. The observed host-parasite interactions at cellular and ultrastructural level are discussed in connection with the still controversial interpretation of the pathogenicity of N. minor.     

Short-term changes in carbon-isotope discrimination in the C3-CAM intermediate Clusia minor L. growing in Trinidad

On-line instantaneous carbon isotope discrimination was measured in conjunction with net uptake of CO₂ in leaves of exposed and shaded plants of the C₃-CAM intermediate Clusia minor growing under natural conditions in Trinidad. At the end of the rainy season (late January-early February, 1992) C₃ photosynthesis predominated although exposed leaves recaptured a small proportion of respiratory CO₂ at night for the synthesis of malic acid. Citric acid was the major organic acid accumulated by exposed leaves at this time with a citric: malic acid ratio of 11:1. Values of instantaneous discrimination () in exposed leaves during the wet season rose from 17.1 shortly after dawn to 22.7 around mid-day just before stomata closed, suggesting that most CO₂ was fixed by Rubisco at this time. During the late afternoon, instantaneous declined from 22.2 to 17, probably reflecting the limited contribution from PEPc activity and an increase in diffusional resistance to CO₂ in exposed leaves. Shaded leaves showed no CAM activity and CO₂ uptake proceeded throughout the day in the wet season. The decrease in instantaneous from 27 in the morning to 19.2 in the late afternoon was therefore entirely due to diffusional limitation. Leaves sampled in the dry season (mid-March, 1992) had by now induced full CAM activity with both malic and citric acids accumulated overnight and stomata closed for 4–5 h over the middle of the day. Values of instantaneous measured over the first 3 h after dawn (6.4–9.1) indicated that C₄ carboxylation dominated CO₂ uptake for most of the morning when rates of photosynthesis were maximal, implying that under natural conditions, the down regulation of PEPc in phase II occurs much more slowly than laboratory-based studies have suggested. The contribution from C₃ carboxylation to CO₂ uptake during phase II was most marked in leaves which accumulated lower quantities of organic acids overnight. In exposed leaves, measurements of instantaneous during the late afternoon illustrated the transition from C₃ to C₄ carboxylation with stomata remaining open during the transition from dusk into the dark period. Uptake of CO₂ by shaded leaves during the late afternoon however appeared to be predominantly limited by decreased stomatal conductance. The short-term measurements of instantaneous were subsequently integrated over 24 h in order to predict the leaf carbon isotope ratios (_p) and to compare this with the _p measured for leaf organic material. Whilst there was close agreement between predicted and measured _p for plants sampled in the wet season, during the dry season the predicted carbon isotope ratios were 5–9 higher than the measured isotope ratios. During the annual cycle of leaf growth most carbon was fixed via the C₃ pathway although CAM clearly plays an important role in maintaining photochemical integrity in the dry season.     

Allozymic and morphometric variation inLemna minor (Lemnaceae)

Allozymic and morphometric variation was studied in 28 clones ofLemna minor. This variation was compared with the corresponding variation in four clones ofLemna gibba and four clones ofSpirodela polyrrhiza. A high level of allozymic variation was observed among the clones, despite having been grown under uniform laboratory conditions for several years and despite its quasi-exclusive clonal means of propagation. Based on degree of allozymic similarity,Spirodela polyrrhiza was distinguished from the twoLemna species but the latter species were genetically indistinguishable. Allozymic similarity among clones ofLemna minor was not related to morphometric similarity, nor was it related to the degree of geographic separation or climatic similarity of their sites of origin. The results suggest that allozymic variation among these clones ofLemna minor may be largely neutral and not a consequence of differential selection.     

Association of polyphosphate with protein in freeze-substituted sclerotia ofSclerotinia minor

Summary In freeze-substituted sclerotia stained with aqueous toluidine blue O, metachromatic material was found throughout the cytoplasm in discrete granules. It was also distributed evenly throughout spherical and elongate protein bodies. This material stained at low pH and was extracted by cold acid, indicating that it was polyphosphate. Retention of metachromatic material was much greater than previously reported in chemically fixed, conventionally processed sclerotia. X-ray microanalysis of dry-cut, unstained sections of freeze-substituted sclerotia confirmed that phosphorus was distributed evenly throughout the protein bodies and was not localised in discrete granules but phosphorus levels in the cytoplasm were very low. It is concluded that polyphosphate is lost during conventional preparation procedures but retained in dry-cut, unstained sections of freeze-substituted material. However, when freeze-substituted sections were stained with toluidine blue O, water soluble polyphosphate was extracted and subsequently precipitated in the cytoplasm as polyphosphate granules. Therefore it is considered that polyphosphate granules are an artefact, and that protein bodies are the major site for storage of phosphorus in this fungus.Abbreviations STEM scanning transmission electron microscope - ER endoplasmic reticulum     

Cryopreservation of hairy root cultures of Vinca minor (L.) by encapsulation-dehydration

Hairy root cultures of Vinca minor and Ajuga reptans var. atropurpurea could be cryopreserved when the roots were precultured and encapsulated in 2% (w/v) alginate beads with 0.3 M sucrose and 0.5 M glycerol and dehydrated until the bead weight reached 25% of the initial weight before cooling in liquid nitrogen. Preculture and encapsulation of the roots with abscisic acid was effective in increasing the survival rates. For V. minor root tips moreover a sufficiently high survival rate of more than 70% was attained by eliminating glycerol from the preculture medium and dehydration of beads until 23% of the initial weight was reached instead of 25%.     

Phenotypic plasticity inLemna minor (Lemnaceae)

Eight genotypes ofLemna minor, originating from four continents, were grown for 15 days in eight different environmental treatments. Fronds under each treatment were then transferred into each of the eight environmental conditions for 15 days. The rate of frond production (relative growth rate) and mean frond biomass were recorded for each pre- and post-transfer treatment and root length was measured for each pre-transfer treatment. For all the traits, the levels of response varied significantly between genotypes (G) and between environmental conditions (E). G × E interaction effect was significant for all traits under pre-transfer treatments and some post-transfer treatments. Both pattern and amount of plasticity were genotypically variable but the amount of variation depended on the trait. The trait representing the best estimate of fitness, growth rate, exhibited the least amount of plasticity and on average, showed the most conservative pattern of plasticity. In contrast, the trait least related to fitness, root length, was the most plastic and showed the most divergent pattern of plasticity. Under some post-transfer treatments, growth rate and mean frond biomass were affected by origin (initial treatment) effect. Pattern and amount of plasticity were also influenced by initial treatments. Since some genotypes may be more affected than others by environmental conditions, origin effect may accentuate G × E interaction and therefore, modify the pattern and amount of plasticity. Comparison between dendrograms based on genetic and phenotypic similarities suggested that there is no relationship between genetic and phenotypic divergence. This lack of relationship may be due to the fact that plasticity is not necessarily adaptive.     

Life cycle and growth ofTrichostegia minor (Curtis) in temporary woodland pools (Trichoptera: Phryganeidae)

Larvae of the caddisTrichostegia minor (Curtis) were collected from four woodland pools in The Netherlands, three of which are temporary, from August 1986 till June 1987. Eggs and larvae of this species proved to be very well adapted to drought, freezing, strongly fluctuating pH and alkalinity levels and prolonged oxygen deficit. The life cycle ofT.minor in a small woodland marsh overgrown byCalla palustris took one year. Adult flight period started at the end of May. Oviposition took place independent of water. Hatching of the eggs started in September and was probably induced by immersion. During the larval stage from September until May, 5 instars could be distinguished by the size of the head capsule. Growth of instars I, II and III during autumn was moderate. Most larvae overwintered as instar III or IV. Possibly there was a larval diapause during winter. In spring rapid growth to instar V took place prior to pupation. Growth rate, expressed as the increase of mean individual dry weight was highest from March to April (2.05±0.75% DW.m^–2.d^–1). In extremely shallow water growth in spring was initially more rapid compared to growth in deeper water. During winter the growth rate decreased to 0.038±0.071% DW.m^–2.d^–1. Net annual production based on the changes of momentary biomass was 183.2±31.7 mg DW.m^–2.y^–1 or 177.2±31.3 mg AFDW.m^–2.y^–1. Production loss during the winter season was 75.1±10.8 mg DW.m^–2.y^–1 or 72.3±10.6 mg AFDW.m^–2.y^–1.