Hydrocarbons,free fatty acids,and amino acids of sclerotia of Sclerotinia sclerotiorum

Summary Sclerotia of Sclerotinia sclerotiorum (Lib.) D By. were obtained from commercial pea-and bean-cleaning operations or grown on potato-dextrose agar and synthetic glucose-and sucrose-salts agar media. The crude fat (ether extract) content of sclerotia varied from 0.8 to 1.5%. Extraction and fractionation of the lipids followed by gas chromatographic analysis showed that sclerotia from pea cleanings contained one predominant hydrocarbon which was absent from sclerotia produced in the laboratory. Sclerotia from natural sources and grown in the laboratory contained a similar distribution of C₁₈ unsaturated free fatty acids, however, quantitative differences were noted. Palmitic, oleic and linoleic were the major free fatty acids of the laboratory-grown sclerotia while a high proportion of linoleic acid was also found in sclerotia from natural sources. Sclerotia were fractionated into water-soluble and water-insoluble fractions. After acid hydrolysis of the waterinsoluble fraction, both fractions were analyzed for amino acids. Twenty-one compounds, including 2 unknowns, were detected in the soluble fraction. The hydrolyzates contained 19 amino acids, including the same 2 unknowns. Two compounds tentatively identified as ornithine and -aminobutyric acid were found only in the water-soluble fraction. The relative amino acid composition of the water-insoluble fraction of sclerotia from various sources was fairly constant but the arginine content decreased on the synthetic media.     

Reserve substances inPaxillus involutus sclerotia

Summary The ectomycorrhizal fungus,Paxillus involutus, produces sclerotia in culture. These can be induced to form on agar medium by exposing mycelium grown at 25°C to various temperatures between6°C and 15°C. Sclerotia formed at 10°C and above were large and covered with drops of exudate, while those formed at 6°C or 8°C were very small and did not produce an exudate. Mature sclerotia were bounded by a compact rind and contained abundant storage reserves. Histochemistry of the larger sclerotia showed large quantities of protein stored as protein bodies in the cytoplasm, lipid present as small droplets, glycogen granules stored in the cytoplasm and polyphosphate present as small granules in the cytoplasm and in the protein bodies. Energy dispersive X-ray microanalysis confirmed the presence of phosphate in the granules and was used to map its distribution throughout the sclerotium. The smaller sclerotia induced at 8°C and below on the same medium had the same basic structure and composition, but lacked the complex phenolic cell network found in large sclerotia, and had abundant extracellular polysaccharides. The rind was not well developed and these small sclerotia are interpreted to have been arrested at an early stage of development.     

Factors Affecting Biological Control of Sclerotinia sclerotiorum by Fungal Antagonists

Studies were conducted to determine the effects of soil moisture (9, 16 or 24% w/w) and temperature (5, 15, 20 or 25°C) on the control of sclerotia of Sclerotinia sclerotiorum by five fungal agents in sterile and natural field soil. All five biocontrol agents were effective in reducing the survival of sclerotia of S. sclerotiorum in sterile soil under dry (9% moisture) or wet (24% moisture) conditions at 20°C, but only Coniothyrium minitans was effective in natural soil. Coniothyrium minitans was the most effective in reducing sclerotial viability at the temperature range of 15–25°C. Trichoderma virens was effective against sclerotia of S. sclerotiorum to a lesser extent than C. minitans , and in non-autoclaved soil, it performed best at 25°C. Although Epicoccum purpurascens , Talaromyces flavus and Trichothecium roseum were effective against sclerotia of S. sclerotiorum in some instances, they were less effective than C. minitans and T. virens . Sclerotia of S. sclerotiorum conditioned for myceliogenic germination were more vulnerable to attack by the biocontrol agents than dormant sclerotia. The implications are discussed with respect to enhancement of biological control of crop diseases caused by S. sclerotiorum in different geographic regions.     

The Respiration Rate of Tomato Stem Tissue Infected by Tomato Aucuba Mosaic Virus

The oxygen uptake of stem tissue slices of Lycopersicum esculentumvar. ‘Stonor's Moneymaker’, in 0·035 M. Sorensonphosphate buffer was measured manometrically; the optimum pHwas found to be 5·2. With tomato-stem tissue systemicallyinfected by virus (tomato aucuba mosaic), the respiration ratewas always below that of healthy tissue when equal numbers ofrespiratory systems were compared. When the respiration ratewas expressed in terms of oxygen uptake per unit fresh or dryweight, the respiration rate of the virus-infected tissue couldbe greater or less than that of the healthy tissue dependingon the growth conditions of the experimental material. Underconditions favouring the complete development of disease symptoms,virus infection decreased the fresh and dry weight of the cell.For this reason fresh weight and dry weight were not consideredsuitable criteria to express the respiration rates as theseunits contained different numbers of respiratory systems inhealthy and virus-infected tissue.     

Prolific production of sclerotia in soil by Rhizoctonia solani anastomosis group (AG) 11 pathogenic on lupin

Rhizoctonia solani anastomosis group (AG) 11 causes serious damping‐off and hypocotyl rot of narrow‐leafed lupins (Lupinus angustifolius) in the northern grain‐belt of Western Australia. R. solani AG‐11 produced abundant sclerotia in sand overlaid on potato dextrose agar. Sclerotia were produced in larger numbers in natural Lancelin sand than in Geraldton loamy sand collected from the northern grain‐belt of Western Australia. The majority of the sclerotia produced were in >250 to <500 μam size range. The germination levels of sclerotia in the first two cycles of drying and germination were not significantly different. Sclerotia still retained 50% germination after four such cycles, indicating that they may have the ability to withstand the climatic cycles of the Mediterranean environment of southwestern Western Australia. The radial growth of the mycelium from sclerotia, however, declined with each drying and germination cycle. Inoculum potential of the pathogen increased with the size of sclerotia resulting in more severe lupin hypocotyl rot with larger sclerotia. The number of sclerotia produced in soil increased with increasing density of lupin seedlings. The results also indicate that R. solani AG‐11 can produce sclerotia on infected plant tissues as well as in soil. This is the first report of the prolific production of sclerotia by AG‐11 and their significant role in infection of lupins in soil in Western Australia.     

Studies on the Growth in Culture of Plant Cells: II. CHANGES IN RESPIRATION RATE AND NITROGEN CONTENT ASSOCIATED WITH THE GROWTH OF ACER PSEUDOPLATANUS L. CELLS IN SUSPENSION CULTURE

Changes in nitrogen content and in respiration rate have beeninvestigated in cell suspension cultures of Acer pseudoplatanus.Nitrogen content and rate of oxygen uptake rise sharply earlyin the period of culture, during which there is no significantincrease in dry weight and only a small increase in cell number.During the subsequent period of rapid cell division there isa decline in both respiration rate and nitrogen content permg dry weight or per cell. Pronounced rises in respiration rateand cell nitrogen therefore occur prior to the period of rapidcell division. The strong correlation between nitrogen contentand oxygen consumption suggests that the respiration rate ismuch more closely related to changes in protein content thanto changes in cell number, dry weight, or packed-cell volume.     

Carbon sources,growth, sclerotium formation and carbohydrate composition of Sclerotinia sclerotiorum

Summary Sclerotinia sclerotiorum (Lib.) D By. was grown in stationary liquid mineral-salts medium, pH 4.3, containing various carbon sources and the weight of mycelia and sclerotia was determined at regular intervals. When grown on various glucose concentrations (0–24 g of C/l), more sclerotia were produced at 8–12 g of C/l. Sclerotia were not usually formed in shake cultures. The ability of the fungus to use other carbon sources for growth and sclerotium formation was tested at 12 g of C/l in the stationary mineral-salts medium. The highest weights of mycelia and sclerotia occurred with raffinose, sucrose, maltose, lactose, d-mannose, d-glucose, d-fructose or l-arabinose. Good growth but decreased sclerotium production were found on cellobiose and d-xylose. Reduced or poor growth, a long lag period and few or no sclerotia occurred on trehalose, melibiose, l-sorbose, l-rhamnose, d-ribose, d-arabinose, l-xylose or 8 polyols. No growth was observed with erythritol or i-inositol. A combination of glucose plus trehalose or polyols resulted in increased growth and the formation of sclerotia. Organic acids supported little or no growth and no sclerotia were produced. Generally culture filtrates which supported growth and formation of sclerotia became acid (about pH 3.5). The pH of the culture filtrate usually increased slowly during the growth period when the fungus grew poorly and no sclerotia were formed. The alcoholsoluble sugars and polyols present in culture filtrates, mycelia and sclerotia were determined by paper and thin-layer chromatography. Regardless of the carbon source, mannitol was usually present in culture filtrates. The occurrence of other compounds in the filtrates depended on the carbon source. Trehalose, mannitol and usually small quantities of glucose or fructose were present in mycelia and sclerotia from all carbon sources. Galactitol or pentitols occurred in mycelia and sclerotia when the fungus grew on galactose and oligosaccharides containing galactose or the corresponding pentose, sugars. Acid hydrolyzates of the alcohol-insoluble fraction of mycelia or sclerotia contained glucose, smaller amounts of galactose and mannose and traces of ribose and rhamnose.     

Oxygen consumption and ammonia excretion of herbivorous chironomid larvae in Lake Balaton

The oxygen consumption and ammonia excretion of a herbivorous midge larva,Chironomus sp., inhabiting Lake Balaton was measured at two different temperatures. The loss of energy through respiration and that through ammonia excretion were calculated. The daily respiratory energy loss amounted to 655.5 ± 123.8 J g^–1 at 17 °C and to 1 160.0 ± 168.4 J g^–1 (dry weight) at 25 °C. Mean energy loss through ammonia excretion was about 40% less than through respiration.     

Germination of sclerotia of Botrytis tulipae, the cause of tulip fire

Sclerotia of Botrytis tulipae (Lib) Lind. buried in field soil germinated mainly in winter and early spring to produce conidiophores and conidia and then decayed. Except when buried very late in the year sclerotia germinated and decayed in the season following burial. In the laboratory, sclerotia from pure culture germinated in two ways. On sterile water-agar they formed colourless mycelium but no conidiophores; the rate of germination was greatest at 25 d?C. On unsterile filter paper and on soil they produced mainly conidiophores and conidia; the rate of germination was greatest at 5 d?C and was enhanced by previous cold treatment. It was unaffected by soil-moisture or pH. Primary infections of tulips arose from sclerotia placed in the soil but only when they were close to the shoot tip or developing stem. It is suggested that, because of their limited survival, soil-borne sclerotia are of importance only when tulips are planted in annual succession.     

Moisture content and CO2 exchange of lichens

Summary Net photosynthesis (10 klx light intensity, 150 E m^-2 s^-1 PAR) and dark respiration of the lichen Ramalina maciformis at different temperatures are measured in relation to thallus water content. Both first increase with increasing hydration. Dark respiration then remains constant with increased water content until thallus saturation. In contrast, a further increase in water content leads to a depression of net photosynthesis, as shown in previous studies, after a maximum of CO₂ uptake has been attained. However, the extent of this depression depends strongly on temperature. In saturated thalli (160% water content in relation to lichen dry weight) the depression amounts to about 15% and 63% of the maximum unsaturated rate at 5°C and 25°C thallus temperature, respectively. The moisture compensation-point of net photosynthesis is also decisively determined by temperature (for 0°C at 20% water content; for 25°C at 15%), and the water content that allows maximum rates of CO₂ uptake (for 0°C at 80%; for 25°C at less than 40% water content). An electrical analogue of CO₂ exchange in a lichen thallus is presented, and it is suggested that the experimental results may be interpreted in terms of temperature-dependent CO₂ diffusion resistances in imbibed lichen thalli.     

Redheadia quercus gen. et sp. nov., the teleomorph of Mycopappus quercus, the frosty mildew fungus in Quercus acutissima

The teleomorph of Mycopappus quercus causing frosty mildew in Quercus acutissima is described as a new genus and species, Redheadia quercus, in the Sclerotiniaceae. Apothecia sprout from sclerotia on the fallen infected leaves kept for 10 months at 5°C and subsequent incubation at 15°C under diffused room light. Typical zonate lesions and multicellular propagules of M. quercus are produced on Q. acutissima, by mycelial inoculation using an isolate from a single ascospore, confirming the teleomorph–anamorphic connection. No significant differences are observed between cultured colonies of isolates from the ascospore and those from the propagule. Sclerotia and microconidia of the fungus are produced on culture media.     

The physiological basis of seed dormancy in Avena fatua. VII. Action of organic acids and pH

Citric, succinic, fumaric, malic, pyruvic and lactic acids induced germination in two genetically pure dormant lines of Avena fatua L. The sensitivity to these acids was low immediately after harvest and increased markedly after a period of dry after-ripening. Because the acids could only overcome dormancy in partly after-ripened caryopses, the mode of their action in these caryopses differed from that of another germination promotor, ethanol, and was similar to that of the germination promoter, sodium nitrate. The mode of action of the organic acids on the partly after-ripened caryopses through lowering pH was indicated by the observation that other non-metabolic weak acids could also break dormancy while neutral pH value salt solutions of some of the tested acids were inactive. The dose-response curves of citric acid for the stimulation of germination and for oxygen uptake were similar, indicating that this organic acid may stimulate germination by promoting oxygen uptake. A time sequence study showed that citric acid stimulated oxygen uptake before the first visible signs of germination. Stimulation of germination and oxygen uptake over a range of pH values showed that those values of pH which stimulated germination also stimulated oxygen uptake, indicating that the ability to stimulate oxygen uptake was not confined to organic acids. The stimulation of both germination and oxygen uptake by citric acid was not inhibited by salicylhydroxamic acid, an inhibitor of alternative respiration, therefore stimulation of both germination and oxygen uptake by citric acid does not require the operation of the alternative pathway of respiration. The function of weak acids as promoters of oxygen uptake is discussed with reference to the breakage of dormancy in partly after-ripened caryopses and the involvement of various respiratory pathways is indicated.     

Air Breathing and Gill Ventilation Frequencies in Juvenile Tarpon, Megalops atlanticus: Responses to Changes in Dissolved Oxygen, Temperature, Hydrogen Sulfide, and PH

This study quantified the air-breathing frequency (ABf in breaths h^–1) and gill ventilation frequency (Vf in ventilations min^–1) of tarpon Megalops atlanticusas a function of PO₂, temperature, pH, and sulphide concentration. Ten tarpon held at normoxia at 22–33°C without access to atmospheric oxygen survived for eight days, and seven survived for 14 days (at which point the experiment was terminated) suggesting that the species is a facultative, rather than an obligate, air breather. At temperatures of 29°C and below ABf was highest and Vf was lowest at low oxygen partial pressures. Tarpon appear to switch from aquatic respiration to air breathing at PO₂levels of roughly 40 torr. The gills were the primary organ for oxygen uptake in normoxia, and the air-breathing organ the primary mechanism for oxygen uptake in hypoxia. At 33°C, both ABf and Vf were elevated but highly variable, regardless of PO₂. There were no mortalities in tarpon exposed to total H₂S concentrations of 0–232µM (0–150.9µM H₂S); however, high sulfide concentrations resulted in very high ABf and Vf near zero. Vf was reduced when pH was acidic. We conclude that air breathing provides an effective means of coping with the environmental conditions that characterize the eutrophic ponds and sloughs that juvenile tarpon typically inhabit.     

Mycoparasitism by Coniothyrium minitans on Sclerotinia sclerotiorum and its Effect on Sclerotial Germination

Scanning electron microscopy showed that hyphae of Coniothyrium minitans produced appressorium-like swellings when they came in contact with Sclerotinia sclerotiorum in dual culture on PDA. The parasitized hyphae gradually skrank and collapsed, and hyphae of the mycoparasite were found inside the host hyphae. The mycoparasite hyphae grew inter- and intracellularly within the sclerotia of S. sclerotiorum. In the later stages of parasitism, hyphae of the mycoparasite proliferated extensively within the sclerotia and formed pycnidia near the sclerotial surface. At this stage, the sclerotia became flattened, soft and disintegrated. Sclerotia parasitized by C. minitans failed to germinate either myceliogenically or carpogenically.     

Population dynamics and energy budget of Marionina southerni (Cernosvitov) (Enchytraeidae,Oligochaeta) in the shallow littoral of Lake Esrom,Denmark

Marionina southerni (Cernosvitov) was numerically the dominant oligochaete in a shallow, strongly exposed surf zone locality (0–1 m depth) in the mesotrophic Lake Esrom. It comprised 21,500 ind m^–2 or nearly 50% of the total oligochaete community, which otherwise was dominated by Nais spp. and the lumbriculid Stylodrilus heringianus Claparède. M. southerni appears to have a 1-y life cycle. Individual biomass ranged from 3 to 48 µg ash free dry weight. Annual net production at the site was 5.1 kcal m^–2 (size-frequency method) with a P/B ratio of 2.5. This is about 0.5% of the estimated mean zoobenthic production in the littoral zone from 0 to 2 m depth in Lake Esrom. At 5° C M. southerni showed a constant oxygen uptake down to 25% oxygen saturation, but practically no regulatory respiration was found at 20 °C. In the field M. southerni was never found in sediment with less than 60% oxygen saturation. The annual community respiration of M. southerni was 14.2 kcal m^–2, and annual assimilation thus made up 19.3 kcal m^–2 with a net production efficiency of 26.5%.     

Induction of edible sclerotia of Pleurotus tuber-regium (FR) Sing, in the laboratory

In the field, sclerotia of Pleurotus tuber-regium were found in dead trees and fallen logs of Daniella oliveri. Sclerotia of P. tuber-regium were produced in the laboratory when the fungus was cultured in moist drill dusts of D oliveri and Elaeis guineensis. The resulting sclerotia were viable and had features similar to those found in the natural habitat.     

Factors influencing respiration data in freshwater sediment

Sediment respiration (oxygen consumption and CO₂ evolution) was measured in freshwater sediment samples using both flask- and core-microcosms, and the estimates were compared. Oxygen consumption data were also compared in flask-microcosms constructed with sediment samples of different masses, sediment: water ratios, and storage times. Furthermore, sediment respiration was examined under different incubation conditions of temperature and agitation. O₂ consumption was markedly higher in flask-microcosms than in sediment core-microcosms, when compared on a per g dry weight basis. However, when the results were expressed as O₂ consumed per unit surface area, the values were more similar. CO₂ evolution was less dependent on surface area as evidenced by similar CO₂ values per g sediment in both microcosms. In addition, the effect of sediment mass on O₂ consumption and CO₂ evolution was examined. Both O₂ consumption and CO₂ evolution (expressed as µmole g^–1 dry weight sediment) decreased significantly with increasing sediment mass between 3 and 12 g dry weight. Maximum O₂ consumption per unit headspace was measured when a wet sediment mass between 10.0 and 20.0 g was used in the flask-microcosms. It was also shown that the sediment: water ratio, agitation, incubation temperature, and previous storage time of sediment all affected the respiration estimates. Initial O₂ consumption and CO₂ evolution in flasks were significantly higher in flasks with a decreased sediment: water ratio (1:1 versus 1:2), increased flask agitation, and increased incubation temperature (15 °C versus 5 °C). Also, respiration decreased significantly over the first 100 days of storage at 4 °C.     

Non-existence of an optimum leaf area index for the production rate of white clover grown under constant conditions

Single clover plants were grown in the vegetative state, at 20 ± 1°, 85 ± 5% relative humidity, 320 ± 10 ppm CO₂, 12-hour day, with Hoagland nutrient in Perlite, and 100 w · m⁻² of photosynthetically active radiation (0.4-0.7 μ) from mercury-fluorescent lamps. Each plant was confined within a circle 18 cm in diameter by means of a wire framework. The CO₂ exchange rate of the whole plant was measured every second day for 3 months. There was no optimum leaf area index for the net photosynthesis rate. The respiration rate was determined mainly by the gross photosynthesis rate and only partly by the amount of non-photosynthetic or heavily shaded tissue. At the maximum leaf area index, when leaves were dying as fast as they were being produced, both photosynthesis and respiration remained at or near their maximum rates. At the end of 3 months, the whole plant was harvested and the dry weight and carbon content determined. The measured dry weight was close to that calculated from the total CO₂ uptake and a constant ratio of carbon content to dry weight of 39%. Optimum leaf area indices observed in field experiments are attributed to the failure to include the material which dies between harvests, and to decreases in the gross photosynthesis rate caused by climate changes or lack of nutrient, for example. The difference between production rate and growth rate or yield is emphasized.     

Feeding dynamics and respiration of the bottom-dwelling caridean shrimp Nauticaris marionis Bate, 1888 (Crustacea: Decapoda) in the vicinity of Marion Island (Southern Ocean)

The feeding dynamics and oxygen uptake of the bottom-dwelling caridean shrimp Nauticaris marionis were studied during the April/May 1984, 1996 and 1997 cruises to Marion Island (Prince Edward Islands, Southern Ocean). N. marionis is thought to have an opportunistic feeding mode. Prey composition varied considerably between the years and sites investigated. Overall, benthic (mainly hydrozoans and bottom-dwelling polychaetes) and, at times, pelagic (largely euphausiids and copepods) prey items dominated in the stomachs of N. marionis both by occurrence and by volume. Generally, pelagic prey contributed more to the diets of smaller shrimps, while benthic prey was a more important component in the guts of larger specimens. Wet, dry and ash-free dry weight were determined for specimens used in respiration experiments. The respiration rates of N. marionis females with carapace length 6.6–11.1 mm ranged from 80 to 250 μl O₂ individual⁻¹ · h⁻¹, or from 0.588 to 2.756 μl O₂ · mg⁻¹ dry weight h⁻¹. Regression analyses showed highly significant correlations between oxygen consumption and carapace length for N. marionis. Daily ingestion rates estimated using an in situ gut content analysis technique (4.4% of body dry weight) and an energy budget approach (average 4.7% of body dry weight, range 2.0–7.5%) showed good agreement with each other. Accepted: 29 July 1998     

Effect of Moisture and Temperature on the Survival of Sclerotia of Sclerotium rolfsii in Soil

The sclerotia of Sclerotium rolfsii Sacc. survived in natural soil for 225 days under controlled moisture at 50% water holding capacity (WHC) after which there was a progressive reduction in the population of viable sclerotia. At 390 days only 48% were recovered. Sclerotia survived well at moisture contents upto 75% WHC but at 100% the population declined rapidly and none were recovered after 60 days. The contents of the sclerotia were found to lyse without germination leaving hollow rinds. Such lysis was found to be favoured between 25 and 40°C. At and below 20°C no such lysis was recovered and more than 80% sclerotia were recovered even after 60 days.