The biology and autecology of Nitraria L. in Australia. I. Distribution,morphology and potential utilization

Nitraria billardieri occurs in all mainland states of Australia and on several adjacent islands south of the Tropic of Capricorn between Lat. 25° and 38°S and Long. 113° and 147°E. Other species of Nitraria are found in North Africa, the Middle East and Eurasia. The probability that Nitraria is a very old genus, having its origins in central Asia, is discussed. The wide disjunction between N. billardieri in Australia and the closely related N. schoberi in eastern Europe and Asia is difficult to explain. Observations on various populations grown under nursery conditions at Deniliquin, combined with those undertaken during field traverses across Australia, clearly indicate that considerable inter-population variability occurs. Whether these different forms are ecotypes in which particular characters have become genetically fixed in specific habitats, is uncertain; but the form growing along the Indian Ocean coast of Western Australia shows marked contrasts to the other forms and may ultimately be described as a distinct species. Possible uses for N. billardieri in arid and semi-arid zones of Australia are discussed. Particular reference is made to the abundance of N. billardieri in low shrubland communities which were dominated by chenopods prior to the introduction of domestic livestock. The marked increase in N. billardieri on overgrazed saltbush (Atriplex vesicaria) communities of the Riverine Plain suggests that it may serve as an indicator species in range condition assessment of these communities.     

Effect of Salinity on Seed Germination,Growth, and Ion Accumulation of Atriplex patula (Chenopodiaceae)

Seeds and seedlings of the halophyte Atriplex patula were exposed to 0–2% NaCl to determine the effect of salt stress on germination and growth. Seeds germinated and plants survived and grew in solutions of up to 2.0% NaCl. Both seed germination and dry mass production were negatively affected by increased salinity. Dry mass production declined to 1% of controls and seed germination to 17% of controls in the 2% NaCl treatments, indicating that seeds were less inhibited than growing plants. Also, recovery treatments indicated that high salinity did not permanently injure seeds. Percent ash, and Na⁺ and Cl⁻ ions increased in shoots with each salt increment, while the K⁺ ion content decreased sharply. Atriplex patula is a facultative halophyte, and is limited to low and moderately saline sites because both seed germination and growth are severely reduced at salinities > 1% NaCl.     

Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a criticalinfluence on the germination of halophyte seeds and plant establishment.Salinity affects imbibition, germination and root elongation.However, the way in which NaCl exerts its influence on thesevital processes, whether it is through an osmotic effect ora specific ion toxicity, is still not resolved. Dimorphic seedsof the halophytesAtriplex prostrataandA. patulawere treatedwith various iso-osmotic solutions of NaCl and polyethyleneglycol (PEG). For each treatment, imbibition, germination rate,percent germination, germination recovery and nuclear area ofroot tip cells were compared. Higher concentrations of NaCl(-1.0 MPa) were more inhibitory to imbibition, germination andseedling root elongation than iso-osmotic PEG solutions. Allseeds recovered from a pre-treatment with -2.0 MPa NaCl andPEG solutions, except large seeds ofA. prostratawhich failedto germinate following transfer from -2.0 MPa NaCl. NaCl causeda greater increase in nuclear volume than iso-osmotic PEG solutions.These data suggest that the influence of NaCl is a combinationof an osmotic effect and a specific ion effect.Copyright 1998Annals of Botany Company Atriplex patula,Atriplex prostrata,cytophotometry, osmotic potential, salinity, seed germination.     

Field inoculation of sorghum and rice withAzospirillum spp. andHerbaspirillum seropedicae

Two field experiments were carried out at the UAPNPBS experimental station, Seropédica, with two sorghum and one rice cultivars. The establishment, and inoculation effects, ofAzospirillum spp. andHerbaspirillum strains marked with antibiotic resistance were investigated. One grain sorghum (BR 300) and one sugar sorghum (Br 505) cultivar were used.Azospirillum lipoferum strain S82 (isolated from surface sterilized roots of sorghum) established in both cultivars and comprised 40 to 80% of theAzospirillum spp. population in roots and stems 60 days after plant emergence (DAE).Azospirillum amazonense strain AmS91 (isolated from surface-sterilized roots of sorghum) reached only 50%. At 90 DAE, S82 almost disappeared (less than 30% of establishment) while the establishment of AmS91 remained constant in roots and stems. No establishment ofH. seropedicae strain H25 (isolated from surface-sterilized roots of sorghum) orA. lipoferum strain S65 (isolated from the root surface of sorghum) could be observed on inoculated roots. Inoculation with S82, AmS91 or S65 but not withH. seropedicae H25, increased plant dry weight of both cultivars and total N in grain of the grain sorghum. In rice,A. lipoferum Al 121 andA. brasilense Sp 245 (isolated from surface sterilized rice and wheat roots respectively) established in the roots but there was no increase inAzospirillum spp. numbers due to inoculation. None of the strains affected plant growth or rice grain yield.Azospirillum amazonense, A82 andH. seropedicae Z95, which did not establish in roots, significantly enhanced seed germination.     

外源水杨酸对NaCl胁迫下大豆种子萌发和幼苗生长生理的影响

以大豆种子、幼苗为试验材料,采用砂培的方法,研究了0.2mmol·L-1外源水杨酸(SA)对100mmol·L-1 NaCl胁迫下大豆种子萌发、幼苗形态及生物量、膜脂过氧化和抗氧化酶活性的影响。结果显示:NaCl胁迫下,大豆种子萌发和幼苗生长受到显著抑制,且随着胁迫时间的延长(0~3d),大豆幼苗相对电解质渗漏率、硫代巴比妥酸活性产物(TBARS)含量显著升高,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性均明显降低。外源SA促进NaCl胁迫下大豆种子萌发和根茎生长,增加幼苗生物量积累,降低幼苗叶片相对电解质渗漏率和TBARS含量,增强其叶片SOD、CAT、APX活性。研究表明,NaCl胁迫能显著抑制大豆种子萌发和幼苗生长,而一定浓度的外源SA能有效提高NaCl胁迫下大豆种子活力及幼苗抗氧化酶活性,减轻膜脂过氧化程度,缓解NaCl胁迫所造成的伤害,提高大豆幼苗抗盐胁迫的能力。     

Differential responses to salinity help explain the replacement of native Juncus kraussii by Typha orientalis in Western Australian salt marshes

The influence of salinity on Typha orientalis and Juncus kraussii was documented in experiments on germination of seeds and on growth of seedlings and adult, rhizome-bearing plants. Juncus was more salt-tolerant than Typha at all three life-history stages, but salt tolerance increased with plant age for both species. Although seeds of both species germinated at 0 and 5 ppt, the germination data overestimated salt tolerance for Typha. Only the newly emerged seedlings of Juncus were capable of growth after removal from the 5 ppt NaCl solution to fresh water. Typha seedlings that initiated growth at 0 ppt grew well at 5 ppt but not at 10 ppt, while Juncus seedlings were tolerant of 10 ppt. Although the 20 ppt treatment caused high mortality of Juncus seedlings, the 10 ppt treatment mainly reduced growth. Adult plants of Typha, which were collected from the field, survived the 20 ppt treatment, while adult Juncus survived the 40 ppt treatment. The presence of salt (10–40 ppt) shortened the growing season for adult, rhizome-bearing plants of both Juncus and Typha, with a lower maximum and earlier peak in total leaf length and maximum leaf number. Thus, the greater biomass in fresh water was achieved primarily through a longer growth period, rather than a greatly accelerated growth rate. Interactions between the two species were explored in mixed-species culture of both seedlings and adult rhizome-bearing plants. Interspecific interactions were present at low salinity, but results differed for seedlings and adult plants. Typha seedlings failed to outgrow Juncus seedlings (at 5 ppt) but adult plants of Typha outgrew Juncus (at 0 ppt). Relative yields (biomass in mixed/pure pots) for Juncus and Typha seedlings were 0.85 and 0.26 at 5 ppt. Relative yields of adult plants were 0.24 for Juncus and 1.20 for Typha at 0 ppt. For both seedlings and adults, the species that ultimately dominated the mixed-species pots produced just as much total biomass as in pure-species pots, even though initial planting density was half as high. Extrapolating findings to the field situation, it appears that Typha has a narrow regeneration niche. The indication is that Typha could invade Juncus stands only following salinity reduction (allowing seed germination and early seedling growth) and after disturbance disrupts the native vegetation. The combined conditions of prolonged low salinity and open habitat occur where street drains are cut through the salt marsh. The probability of Typha becoming established would be highest in such areas. vegetative expansion would follow with continued freshwater influx, as rhizome-bearing plants gain an interspecific advantage.     

外源水杨酸对盐胁迫下大黄种子萌发及幼苗生长的影响

该研究以掌叶大黄、唐古特大黄和药用大黄种子为材料,采用双层滤纸培养法,设置系列浓度NaCl (0、100、150、200、250 mmol/L) 胁迫试验,以及系列浓度水杨酸(SA)溶液(0、50、100、150、200、250 mg/L)拌种和浸种后盐胁迫实验,测定3种大黄种子萌发及幼苗生长指标,揭示外源水杨酸对盐胁迫下大黄种子萌发及幼苗生长的影响。结果显示：(1)随NaCl浓度增大3种大黄种子的发芽率均呈直线下降趋势,且子叶、胚轴、根和苗等生长均受到强烈抑制。(2)在拌种条件下, 200 mmol/L NaCl胁迫下掌叶大黄苗长在200 mg/L SA处理下受到显著促进; 200 mmol/L NaCl浓度盐胁迫下唐古特大黄种子发芽率在250 mg/L SA处理下受到显著抑制;100 mmol/L NaCl胁迫下药用大黄种子发芽势在200 mg/L SA处理下受到显著抑制,其发芽率在150 mg/L SA处理下得到显著抑制,其苗长在250 mg/L SA处理下受到显著抑制。(3)在浸种条件下, 200 mmol/L NaCl胁迫下掌叶大黄种子发芽率在50 mg/L SA处理下显著提高,其幼苗根长和苗长的生长在250 mg/L SA处理受到显著促进;200 mmol/L NaCl胁迫下唐古特大黄种子的发芽势在200 mg/L SA处理下得到显著促进,其幼苗根和苗的生长在50 mg/L SA处理下得到显著促进;100 mmol/L NaCl 胁迫下药用大黄根和苗的生长在100 mg/L SA处理下均得到显著促进。研究表明,3种大黄种子和幼苗对盐胁迫的响应趋势一致,但对不同浓度SA拌种和浸种的响应有较大差异。     

Development of a new piosphere in arid chenopod shrubland grazed by sheep. 2. Changes to the vegetation

The initial development of a piosphere created by stocking a new watering trough with ca. 200 sheep at a near-pristine site in arid chenopod shrubland near Whyalla, South Australia, was studied. The following variables were monitored for up to 8 years using fenced plots as controls:shrub mortality; forage biomass and defoliation of the dominant shrubs and short-lived grasses; linear dimensions of Rhagodia ulicina; the density of short-lived species; and the invasion of exotics. Patterns in these variables were looked for which reflected the attenuation of stocking pressure with distance from water; that is, ‘piosphere patterns’. Piosphere patterns were detected for many variables. Those with values increasing towards the trough were mortality of the main forage shrub Atriplex vesicaria. the density of three short-lived taxa, viz. the bassias (Sclerolaena obliquicuspis, S. patenticuspis. Maireana sclerolaenoides), Tetragonia tetragonoides, and annual Zygophyllum spp. (Z. crenatum. Z. ovatum), and growth of short-lived grass species when sheep stocking pressure was low. Variables with values decreasing towards the trough were grass biomass, percentage of A. vesicaria individuals in flower, the percentage foliation of A. vesicaria and of the forage shrub Maireana sedifolia, and shrub forage biomass of A. vesicaria and M. sedifolia. The rate at which these patterns were registered varied. After only 3 months, a piosphere pattern was evident for grass biomass. Marrubium vulgare, an introduced weed, invaded the trough site within the first 6 months. Almost no A. vesicaria shrubs had died after 2 years, but after 8 years there was a marked piosphere pattern in their mortality. The piosphere patterns in forage biomass and defoliation of A. vesicaria and M. sedifolia became more pronounced with time. Some variables did not exhibit a piosphere pattern, such as the dimensions of the shrub R. ulicina and the densities of successive cohorts of the forb Erodium spp., even though there was an overall effect of grazing in reducing their values. There was no mortality of two dominant shrubs, M. sedifolia and R. ulicina, during the first 8 years.     

Halophyte and glycophyte salt tolerance at germination and the establishment of halophyte shrubs in saline environments

Saline sites suffer variations in surface salinity, available soil water, temperature, soil crust strength and other factors which can influence germination and establishment. For establishment to occur the germinating seed must capitalise on a window of opportunity. This window can be widened by placing seeds in a low-salt niche, covering the seeds with a mulch (such as vermiculite), spraying the seed and mulch placement with a coating which may stabilise the favourable situation and raise soil temperature. In this paper it is shown that using seeds collected from plants of Atriplex amnicola which produce many volunteer seedlings in their vicinity can assist establishment from direct seeding. These seeds had the ability to germinate under saltier and cooler conditions than seeds from A. amnicola bushes which did not produce volunteers. Seeds of a halophyte (Atriplex lentiformis) and a non-halophyte (Medicago sativa) are able to imbibe water from a saline substrate in a similar manner. The water enables the seeds of both species to mobilise stored growth materials and produce and elongate radicles. When the seedlings try to erect a hypocotyl and spread their cotyledons, the non-halophyte, in a saline medium, becomes flaccid, distorted and dies. The halophyte seedling shows evidence of high salt tolerance in the form of succulence of cotyledons and trichomes on true leaves even before they are visible and goes on to successfully develop a functioning plant. Nevertheless, germination of halophyte seeds is inhibited or severely reduced at salinity levels above 250 mM NaCl and slowed and reduced progressively up to those levels.     

外源H2O2对盐胁迫下小白菜种子萌发和幼苗生理特性的影响

以小白菜"甜脆青"为试材,研究不同浓度（5、10、25、50和100 mmol/L）过氧化氢（H₂O₂）浸种处理对100 mmol/L NaCl胁迫下小白菜（Brassica chinensis L.）种子萌发、幼苗生长及生理特性的影响。结果表明：100 mmol/L NaCl胁迫明显抑制小白菜种子的萌发状况和幼苗生长,发芽势、发芽指数、活力指数及幼苗根和芽长度和鲜重均明显降低,根和芽中CAT的活性及K⁺含量明显受到抑制,渗透调节物质、活性氧和MDA含量显著增加。不同浓度H₂O₂浸种处理提高了NaCl胁迫下小白菜种子发芽势、发芽指数和活力指数,促进小白菜根和芽的生长,增强了NaCl胁迫下根和芽中SOD、CAT和APX的活性及K⁺含量,降低O₂^-·产生速率及H₂O₂和MDA含量,进一步促进脯氨酸和可溶性糖含量的增加,降低体内Na⁺含量。其中以10 mmol/L H₂O₂处理缓解盐胁迫效果最好,明显缓解NaCl胁迫对小白菜种子萌发和幼苗生长的抑制。     

Seasonal variation in allelopathic potential of<Emphasis Type="Italic">Artemisia princeps</Emphasis> var.<Emphasis Type="Italic">orientalis</Emphasis> on plants and microbes

We investigated seasonal variations in allelopathic potential ofArtemisia princeps var.orientalis. Aqueous and meth-anol extracts and volatile substances were prepared in the laboratory from samples collected monthly (April through October). Their impacts were then assessed on the germination and seedling growth ofLactuca sativa andAchyranthes japonica. The allelopathic potential varied with the time of sample collection and the concentration tested. For example, germination ofL. sativa was not inhibited by the aqueous extract but seedling growth (shoots and roots) was, with its seasonal effect being significant. ForA. japonica, seed germination was not inhibited at lower concentrations (except for August samples). However, at higher concentrations and in certain months (especially July), germination was more negatively affected. The degree of seedling growth inhibition also differed by month and by extract concentration, with roots being impacted more than shoots. Volatile substances also had a time-dependent influence on the germination and seedling elongation ofA. japonica. In a separate experiment, the ethyl-acetate and water fractions of a crude methanol extract were prepared monthly fromA. princeps var.orientalis. Here, we examined their antimicrobial activities against three gram-positive bacteria (Bacillus cereus, Bacillus subtilis, andStaphylococcus aureus), two gramnegative bacteria (Escherichia coli andPseudomonas fluorescens), and one lactic acid bacterium,Lactobacillus plantar urn. The ethyl-acetate fraction that was sampled in September was remarkably potent againstB. cereus andB. subtilis, whereas the water fraction collected in August and September showed great antimicrobial activity against the grampositive and -negative bacteria. In contrast,L. plantarum was not inhibited by the water fraction, regardless of the sampling month. Likewise, the ethyl-acetate and water fractions collected in April and October had the lowest levels of antimicrobial activity.     

Bacterial antagonists of Sunflower (Helianthus annuus L.) fungal pathogens

Bacteria isolated on nutrient agar and King's medium B from sunflower leaves, crown and roots inhibited in vitro growth of the leaf spot and wilt pathogens Alternaria helianthi, and Sclerotium rolfsii, respectively, and also the root rot pathogensRhizoctonia solani and Macrophomina phaseolina. Antagonistic bacteria from leaves were mainly actinomycetes and pigmented Gram-positive bacteria, while those from roots and crowns were identified asPseudomonas fluorescens-putida, P. maltophilia, P. cepacia, Flavobacterium odoratum andBacillus sp. In soil bioassays, when used as seed inoculum in the presence ofS. rolfsii, P. cepacia strain N24 increased significantly the percentage of seedling emergence. Bacterial strains which exhibited broad spectrum in vitro antagonistic activity were tested for colonisation of sunflower roots, when used as a seed inoculum. Good colonisers (10⁴ to 10⁶ bacteria/g root) were consistent in their ability to reduce disease and fungal wilt. A seedling having a primary root length < 5 cm with fewer lateral roots, necrosed cotyledons or crown and a wilted shoot indicated its diseased status. On an average, only 30% of seedlings were diseased when treated with the antagonistic strains, in the presence of the pathogen, while 60% of the seedlings were diseased in the presence of the pathogen alone. In microplots treated with strain N24, only 1 to 3% of the seedlings were wilted, while 14% of the seedlings were wilted in the presence of the pathogen alone. The results obtained show that bacterial antagonists of sclerotial fungi can be used as seed inocula to improve plant growth through disease suppression     

Inoculation of pines in a nursery withPisolithus tinctorius andThelephora terrestris in Korea

Summary Mycelial inocula of the two ectomycorrhizal fungi,Pisolithus tinctorius (Pt) andThelephora terrestris (Tt) were artificially introduced into fumigated nursery soil before seed sowing. At the end of the first growing season, Pt stimulated the height growth ofPinus densiflora, P. thunbergii, P. rigida, andP. rigida×taeda by 55, 36, 69, and 37%, respectively, compared with control seedlings (with no fumigation and no inoculation). When growth stimulation was expressed by dry weight, Pt increased dry weight ofP. densiflora andP. rigida×taeda by 143% and 128%, respectively, over control seedlings. Total absorption (per plant top) of nitrogen and phosphorus of inoculatedP. densiflora seedlings was also increased by 188 and 144%, respectively, even though the concentration of these two elements in the tissue was not significantly different from that of control seedlings.Tt failed to stimulate growth of the inoculated plants possibly due to its lower level of infection (40–60% mycorrhizal tips) compared with the relatively high infection (over 80%) of Pt.Pinus koraiensis did not respond to inoculation during the first growing season, probably due to its inherent characteristics of producing a small number of short roots and its slow shoot growth during the first few years after germination.This study was supported by the International Foundation for Science in Stockholm, Sweden.     

Coexistence and interference between a native perennial grass and non-native annual grasses in California

Little is known about the potential for coexistence between native and non-native plants after large-scale biological invasions. Using the example of native perennial bunchgrasses and non-native annual grasses in California grasslands, we sought to determine the effects of interference from non-native grasses on the different life stages of the native perennial bunchgrass Nassella pulchra. Further, we asked whether N. pulchra interferes with non-native annual grasses, and whether competition for water is an important component of these interspecific interactions in this water-limited system. In a series of field and greenhouse experiments employing neighbor removals and additions of water, we found that seedling recruitment of N. pulchra was strongly seed-limited. In both field and greenhouse, natural recruitment of N. pulchra seedlings from grassland soil was extremely low. In field plots where we added seeds, addition of water to field plots increased density of N. pulchra seedlings by 88% and increased total aboveground N. pulchra seedling biomass by almost 90%, suggesting that water was the primary limiting resource. In the greenhouse, simulated drought early in the growing season had a greater negative effect on the biomass of annual seedlings than on the seedlings of N. pulchra. In the field, presence of annuals reduced growth and seed production of all sizes of N. pulchra, and these effects did not decrease as N. pulchra individuals increased in size. These negative effects appeared to be due to competition for water, because N. pulchra plants showed less negative pre-dawn leaf water potentials when annual neighbors were removed. Also, simply adding water caused the same increases in aboveground biomass and seed production of N. pulchra plants as removing all annual neighbors. We found no evidence that established N. pulchra plants were able to suppress non-native annual grasses. Removing large N. pulchra individuals did not affect peak biomass per unit area of annuals. We conclude that effects of interference from non native annuals are important through all life stages of the native perennial N. pulchra. Our results suggest that persistence of native bunchgrasses may be enhanced by greater mortality of annual than perennial seedlings during drought, and possibly by reduced competition for water in wet years because of increased resource availability. Received: 12 November 1998 / Accepted: 4 August 1999     

Embryo culture and taxane production inTaxus spp

Summary We have previously shown (Flores and Sgrignoli, 1991) that immature embryos ofTaxus brevifolia andT. X media are capable of precocious germination and can grow into seedlings in vitro. The cultural and environmental parameters for embryo germination and conversion into seedlings have been optimized and extended toT. baccata andT. cuspidata. A 14-h photoperiod improved embryo germination and growth into seedlings. A pregermination cold treatment of the seeds had a positive effect on both the onset and percentage of germination. Embryos from cold-treated seeds germinated earlier and at a higher frequency than those from control seeds. Boron was necessary for embryo germination, and levels of this micronutrient were established for optimal growth and germination ofT. brevifolia andT. X media cv. Hicksii embryos. Gupta and Durzan’s medium was superior to White’s for embryo germination and root formation. Naphthaleneacetic acid stimulated root formation in embryo-derived seedlings. We also found that immature embryos could be induced to form callus with embryogenic potential. Taxol and related taxanes were detected in embryo- derived seedlings.     

Pollenfertility and seed formation in theOrnithogalum umbellatum/angustifolium complex (Liliaceae/Scilloideae)

The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984).     

Autecology of Acacia Senegal (L.) Willd.

Acacia senegal (L) Willd. is a small sized tree species of Tropical arid region of Southern West Pakistan. It is well-known for producing gum arabic. Fruits from dry streams with loamy sand soil type were of bigger size whereas seed output per pod and seed weight were higher in hilly regions. The seeds possess external dormancy (seed coat), which can be broken by mechanical and chemical scarification, water (cold and boiling) and dark treatments. Seeds gave high percentage of germination in fine sand in pot culture. Germination percentage was high in May–July. The growth rate of seedlings both in pot culture and field conditions was high in April, May, June and July. Seeds collected from different localities showed considerable variation in germination capacity. Percentage and rate of germination increased with the lapse of time. Correlation of growth and abundance ofAcacia senegal was found with topography, soil texture, soil structure, soil consistence, maximum water holding capacity, wilting coefficient (sub-surface soil), soil carbonates (surface soil) soil pH (surface soil) and community associates. The plant can be propagated by shoot cuttings. Smaller and thinner cuttings are easily propagated. The plant is infested by Buffaloe tree hopper and is also infected byCladosporium herbarum. Occasionally seedlings are attacked byFusarium sp. The relative turgidity of branches was found to be high throughout the study period, but the leaves showed considerable variation.     

Occurrence and survival ofAzospirillum spp. in temperate regions

In order to evaluate the suitability ofAzospirillum spp. as a crop inoculant in temperate regions, the natural occurrence, distribution and survival ofAzospirillum after seed inoculation in Belgian agricultural soils was studied.Azospirillum was present in most of the fields examined, but concentrations never exceeded 1000 cfu per g soil or per g roots. Under field conditions none of the known species was found to be localized inside the roots of barley, wheat, rye, maize or grasses. Also, the distribution ofA. brasilense SpBr 14 within the root system of hydroponic-grown wheat was studied by immunofluorescence. From the rhizosphere samples of the field crops investigated, a number of microaërophilic, diazotrophic bacteria were isolated and identified asA. lipoferum, found only on maize and grass roots, andA. brasilense, present under all crops. In contrast toA. brasilense, A. lipoferum was able to use different amino-acids and some derivatives as sole carbon and nitrogen sources. Use of a peat-based seed inoculant resulted in the establishment of theAzospirillum spp. in the rhizosphere of field-grown winter barley and winter wheat. The established population survived during winter without appreciable change in numbers, but there was no indication of active growth during spring or summer.     

Influence of soil salt,at levels characteristic of some roadside environments,on the germination of certain tree seeds

Summary Tree seeds were germinated in a greenhouse soil mix amended with varying amounts of sodium chloride. The salt was added in amounts approximating certain roadside soil environments.Betula alleghaniensis, Catalpha bignonioides, Quercus coccinea andQ. cerris seed exhibited reduced germination percentage at the highest salt concentrations. Germination ofRobinia pseudoacacia seed was delayed as salt concentration was increased. Except for slight germination percentage reduction, seed ofAilanthus altissima, Pinus rigida andGleditsia triacanthos were uninfluenced by the salt treatments.     

Failure of a Mycelial Formulation of the Nematophagous FungusHirsutella rhossiliensisto Suppress the NematodeHeterodera schachtii

Research was conducted to determine whether pelletized hyphae ofHirsutella rhossiliensissuppressed invasion of roots by the sugarbeet cyst nematodeHeterodera schachtiiin field microplots. The loamy sand in the microplots was infested withH. schachtiibut not withH. rhossiliensis.Alginate pellets, with or without hyphae ofH. rhossiliensis,were mixed into soil removed from the microplots (1 pellet/cm³of soil). The soil was placed in cylinders positioned vertically in microplots; cylinders (6/microplot) were 10.1 cm wide and 15.3 cm deep and contained 1200 cm³of soil. Pellets and soil also were placed in soil observation chambers, which were buried in the cylinders or kept at 20°C in moisture chambers in the laboratory. After 12 days, cabbage seeds were planted in each cylinder, and after 10 days of growth, the seedlings were removed from the soil andH. schachtiiin the roots were counted. The number ofH. schachtiiin roots was large and was unaffected by addition ofH. rhossiliensis.In soil observation chambers,H. rhossiliensisgrew vigorously from the pellets in heat-treated soil but not in nonheated soil, and enchytraeids and collembolans were observed near damaged pellets. We suspect that organisms, possibly including enchytraeids and collembolans, fed upon or otherwise inhibitedH. rhossil- iensis.