First Records and Microhabitat Assessment of Protostelids in the Aberdare Region, Central Kenya

ABSTRACT. A rapid assessment survey on the occurrence and distribution of protosteloid amoebae was carried out in central Kenya. Samples of dead plant materials were collected from 46 study sites (each 20 × 20 m) situated along an elevation gradient (1,785–3,396 m) that encompassed five major land use/cover types. Twenty-four species and subspecific taxa were recovered and included 23 protostelids and one minute myxomycete, often included in surveys for protostelids. All of these were the first records for Kenya, and six were new for Africa. Numbers of taxa were highest in ground litter and aerial litter microhabitats (20 taxa each) and lowest on aerial bark (10) and ground bark (7). Relative species abundance was greatest in aerial litter, moderate in ground litter, and low on aerial and ground bark microhabitats. The most frequently occurring species on ground litter were Schizoplasmodiopsis pseudoendospora, Schizoplasmodiopsis amoeboidea , and Protostelium mycophaga var. mycophaga , whereas the most common species on aerial litter were P. mycophaga var. mycophaga and Soliformovum irregularis . Species richness and abundance decreased with increasing elevation.     

The actomyosin cytoskeleton of amoebae of the cellular slime molds acrasis rosea and protostelium mycophaga: structure, biochemical properties, and function

In amoebae of the cellular slime molds (mycetozoans) Acrasis rosea and Protostelium mycophaga, bundles of F-actin radiate from the endoplasm-ectoplasm interface into the pseudopodia, where G-actin is also located. We conclude that these actin bundles form a core scaffold driving pseudopod extension which is subsequently completed by filling with a more loosely organized meshwork of F-actin. Some bipolar, elongate amoebae of A. rosea also contained long bundles of F-actin that traverse the cells lengthwise and remotely resemble stress fibers. Rodlets of F-actin were scattered in the body of amoebae of A. rosea or formed star-shaped or polygonal complexes near or around contractile vacuoles, where they may play a role in contraction. In total protein extracts analyzed by SDS-PAGE and immunoblots the actins migrated like the rabbit skeletal muscle control. The relative proportion of actin in total protein extracts was 7.9% for A. rosea and 34.5% for P. mycophaga. We detected four or five isoactins in extracts of both species and we determined that the genome of each species contains approximately six actin genes. Whether they are all expressed or if posttranslational modifications occur remains to be determined. Myosin II was enriched in actomyosin extracts; its Mr was 187.8 kDa for A. rosea and 220.7 kDa for P. mycophaga. Cell models ("ghosts") contracted upon the addition of ATP. We conclude that amoebae of A. rosea and P. mycophaga, although behaving differently from those of Dictyostelium discoideum, contain the basic repertoire of molecules that enable pseudopod extension by actin polymerization and ATP-induced contraction of the cell cortex. Copyright 1998 Academic Press.     

HUMARINA XYLARIICOLA的正确名称

重新研究保存在中国科学院微生物研究所菌物标本馆的真菌上生的盘菌Humarina xylariicola标本, 并与Cenangium xylariicola, Cenangium tahitense, Dermatea mycophaga, Mollisia obconica, Patinellaria cubensis 和Peziza xylariicola的原始描述及模式标本进行比较,研究结果表明,我国报道的Humarina xylariicola形态特征和习性与上述材料完全相同。按照现行的国际植物命名法规,Encoelia cubensis应该是该种的正确名称。     

Nomenclatural notes to Nordic Macromycetes vol. 1 & 3

A new species, Thanatephorus uniygdalisporirs , is described and a number of new combinations and a new name are proposed: Bryoglossum rehmii comb. nov., Lachnellula juniperinu comb. nov., Lactarius torminosulus nom. nov., Lentaria dendroidea comb. nov., Postia ptyhogaster comb. nov., Stecclierinum collabens comb. nov., S. luteoalbum comb. nov., S. nitidum comb. nov., S. pseudozilingiunum comb. nov., S. separabilimum comb. nov., Syzygospora mycophaga comb. nov., Thanatephorus fusisporus comb. nov., Tremella invasa comb. nov., Uncobasidium albidum comb. nov. and Woldmaria filicina comb. nov. A number of notes on clavarioid fungi are given.     

Protostelids from tropical forests, woodlands and deserts in Australia

Most of what is known about the distribution of protostelids is limited to results from surveys carried out in North and Central America. To increase our knowledge about protostelid diversity and distribution we surveyed protostelids from 12 study sites in northern Queensland and the Northern Territory of Australia during May-Jun 2003. Aerial litter and ground litter samples were randomly collected along a 200 m transect at each site. Study sites ranged from tropical forests to deserts. We recovered 10 species and two apparently undescribed species from samples of aerial (dead but still attached plant parts) and ground litter. Samples from a woodland site characterized by intermediate moisture conditions had the greatest species richness, followed by samples from dry woodland, tropical forest and desert sites. When species richness for a particular microhabitat was considered, samples of aerial litter yielded more species than samples of ground litter. Percentages of samples colonized with protostelids were similar for the aerial and ground litter microhabitats within a given habitat type except for dry woodlands, in which aerial litter samples were characterized by higher numbers of species than ground litter samples. Two species (Protostelium mycophaga and Soliformovum irregularis) that in temperate North America are associated with aerial litter microhabitats also were recovered from aerial litter in dry habitats in Australia. Schizoplasmodiopsis pseudoendospora, a North American temperate ground litter species, was equally abundant in aerial litter and ground litter in Australia. This study is the first of its kind for protostelid ecology in Australia and the most extensive study of protostelids in the southern hemisphere. These data complement ongoing research on protostelid distribution from around the world.     

Temperature and water activity minima for growth of spoilage moulds from meat

L owry , P.D. & G ill , C.O. 1984. Temperature and water activity minima for growth of spoilage moulds from meat. Journal of Applied Bacteriology 56 , 193–199.
Five species of fungi were isolated from mould spoilage on meat other than black spot. 'White spot' colonies yielded Chrysosporium pannorum or an Acremonium sp .; 'whiskers' colonies yielded Thamnidium elegans or Mucor racemosus , and blue-green colonies yielded Penicillium corylophilum. Chrysosporium pannorum was moderately xerotolerant with a minimum growth temperature of — 5C. The Acremonium sp. and P. corylophilum showed a similar level of xerotolerance but had a minimum growth temperature of — 2C. Mucor racemosus was no more xerotolerant than many spoilage bacteria and did not grow below - 1C, but grew rapidly at 3C and above. Thamnidium elegans grew at — 7C on supercooled medium and an intrinsic minimum growth temperature of — 10C was indicated. However, the low xerotolerance of this species precluded growth on frozen media below — 5C. It seems therefore that — 5C is the practical limiting temperature for mould growth on meat, and mould spoilage usually indicates that surfaces of freezer stored meats have approached and possibly exceeded 0C.     

Diauxic growth of Agrobacterium tumefaciens 15955 on succinate and mannopine.

Diauxic growth was observed upon incubation of Agrobacterium tumefaciens 15955 on a mixture of succinate and mannopine as the carbon source. Diauxic growth was also observed when either fumarate or L-malate was mixed with mannopine. No diauxie was detectable when A. tumefaciens 15955 was grown on a mixture of mannopine and glucose, fructose, sucrose, or L-arabinose. Preferential utilization of succinate was observed in the initial growth phase of diauxie, whereas the final growth phase occurred at the expense of mannopine. Cells harvested during the initial growth phase exhibited a capacity for uptake of [14C]succinate but not of [14C] mannopine. A capacity for [14C]mannopine uptake was expressed during the final growth phase. Extracts from cells grown on a mixture of succinate and mannopine exhibited a low level of mannopine cyclase activity in the initial phase of diauxie. This activity increased substantially in the final phase of growth. Added succinate had no effect on the rate of [14C]mannopine uptake or mannopine cyclase activities of cells previously grown on mannopine. Diauxie was also observed during growth of strain 15955 on a mixture of succinate and octopine.     

Selection of strains of Lentinula edodes and Lentinula boryana adapted for efficient mycelial growth on wheat straw

Mycelial growth rates are presented for 11 strains of Lentinula edodes and six strains of Lentinula boryana cultivated on solid media: derived from malt extract (MEA); malt yeast extract (YMEA); and, YMEA plus soluble lignin derivatives (YMEA+WSLD). The results were compared with data for mycelial growth rates, of the same strains cultivated on substrates derived from wheat straw treated at different temperatures (50, 65, 75 and autoclaving at 121 degrees C). In general, the addition of WSLD significantly reduced mycelial growth rates in both species. The greatest mycelial growth rate was obtained on sterilized straw at 121 degrees C for the majority of strains. However, this growth was not significantly different from that obtained at 75 degrees C. L. edodes showed greater growth rates than L. boryana. The feasibility of using estimates of mycelial growth rate on YMEA and YMEA+WSLD are discussed as possible indicators of a strain's potential for mycelial growth on substrates derived from wheat straw.     

Effects of temperature on cell growth and xanthan production in batch cultures of Xanthomonas campestris

Batch xanthan fermentations by Xanthomonas campestris NRRL B-1459 at various temperatures ranging between 22 degrees C and 35 degrees C were studied. At 24 degrees C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27 degrees C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35 degrees C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h(-1) at temperatures between 27 degrees C and 31 degrees C. Cell yield decreased from 0.53 g/g glucose at 22 degrees C to 0.28 g/g glucose at 33 degrees C, whereas xanthan yield increased from 54% at 22 degrees C to 90% at 33 degrees C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27 degrees C and 30 degrees C. These results suggest that the optimal temperatures for cell growth are between 24 degrees C and 27 degrees C, whereas those for xanthan formation are between 30 degrees C and 33 degrees C. For single-stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two-stage fermentation process with temperature shift-up from 27 degrees C to 32 degrees C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.     

Studies on the lipid content and phosphate requirement of glucose- and acetate-grown Escherichia coli

1. The phosphate requirement, i.e. the concentration of inorganic orthophosphate that just ceases to be limiting for growth, of Escherichia coli N.C.T.C. 5928 was determined for growth in ammonium-salts media containing glucose or acetate as the carbon and energy source, and compared with that of six other strains of E. coli. 2. The phosphate requirement for E. coli N.C.T.C. 5928 growing on acetate was about ten times that for growth on glucose, but this difference was not observed with any of the other strains. 3. After about 40 generations' growth on acetate with phosphate limitation in a chemostat, the phosphate requirement of the cells gradually decreased until it was equivalent to that of the glucose-grown organism; a single passage through glucose batch culture sufficed to restore the original high phosphate requirement, indicating a permeability phenomenon. 4. The lipid content of E. coli N.C.T.C. 5928 grown on glucose or acetate was measured isotopically by fractionation of cells grown on inorganic [(32)P]orthophosphate and gravimetrically after extraction from the cells by three different methods; change of carbon source from glucose to acetate did not affect the lipid content, which remained constant at 8-9% of the bacterial dry weight.     

Water and temperature relations of growth and ochratoxin A production by Aspergillus carbonarius strains from grapes in Europe and Israel

AIMS: This study investigated the in vitro effects of water activity (a(w); 0.85-0.987) and temperature (10-40 degrees C) on growth and ochratoxin A (OTA) production by two strains of Aspergillus carbonarius isolated from wine grapes from three different European countries and Israel on a synthetic grape juice medium representative of mid-veraison (total of eight strains). METHODS AND RESULTS: The synthetic grape juice medium was modified with glycerol or glucose and experiments carried out for up to 56 days for growth and 25 days for OTA production. The lag phase prior to growth, growth rates and ochratoxin production were quantified. Statistical comparisons were made of all factors and multiple regression analysis used to obtain surface response curves of a(w) x temperature for the eight strains and optimum growth and OTA production by A. carbonarius. The lag phase increased from <1 day at 25-35 degrees C and 0.98 a(w) to >20 days at marginal temperatures and water availabilities. Generally, most A. carbonarius strains grew optimally at 30-35 degrees C, regardless of solute used to modify a(w), with no growth at <15 degrees C. The optimum a(w) for growth varied from 0.93 to 0.987 depending on the strain, with the widest a(w) tolerance at 25-30 degrees C. There was no direct relationship among growth, environmental factors and country of origin of individual strains. Optimum conditions for OTA production varied with strain. Some strains produced optimal OTA at 15-20 degrees C and 0.95-98 a(w). The maximum OTA produced after 10 days was about 0.6-0.7 microg g(-1), with a mean production over all eight strains of 0.2 microg g(-1) at optimum environmental conditions. CONCLUSIONS: This work demonstrates that optimum conditions for OTA production are very different from those for growth. While growth rates differed significantly between strains, integration of the OTA production data suggests possible benefits for use of the information on a regional basis. SIGNIFICANCE AND IMPACT OF THE STUDY: Very little detailed information has previously been available on the ecology of A. carbonarius. This knowledge is critical in the development and prediction of the risk models of contamination of grapes and grape products by this species under fluctuating and interacting environmental parameters.     

Effects of chlorogenic acid,caffeine, and coffee on behavioral and biochemical parameters of diabetic rats

Mesenchymal stem cells (MSCs) represent a potential therapeutic target for glioma. We determined the molecular mechanism of inhibitory effect of human umbilical cord-derived MSCs (hUC-MSCs) on the growth of C6 glioma cells. We demonstrated that hUC-MSCs inhibited C6 cell growth and modulated the cell cycle to G0/G1 phase. The expression of β-catenin and c-Myc was downregulated in C6 cells by conditioned media from hUC-MSCs, and the levels of secreted DKK1 were positively correlated with concentrations of hUCMSCs-CM. The inhibitory effect of hUC-MSCs on C6 cell proliferation was enhanced as the concentration of DKK1 in hUCMSCs-CM increased. When DKK1 was neutralized by anti-DKK1 antibody, the inhibitory effect of hUC-MSCs on C6 cells was attenuated. Furthermore, we found that conditioned media from hUC-MSCs transfection with siRNA targeting DKK1 mRNA or pEGFPN1-DKK1 plasmid lost or enhanced the abilities to regulate the Wnt signaling in C6 cells. Therefore, hUC-MSCs inhibited C6 glioma cell growth via secreting DKK1, an inhibitor of Wnt pathway, may represent a novel therapeutic strategy for malignant glioma.     

Factors affecting steroid and prostaglandin secretion by reproductive tissues of cycling and pregnant sows in vitro

Mitochondrial, microsomal and pellicular membranes were isolated from Tetrahymena cells grown at 39 degrees C or 15 degrees C, and phospholipids, in turn, were separated from total lipids extracted from these membranes. The effect of growth temperature on their solid-to-fluid phase transition temperature was examined by wide-angle X-ray diffraction. The transition temperatures of phospholipids from mitochondria, microsomes and pellicles were 21, 19 and 26 degrees C for cells grown at 39 degrees C and -8, -3 and 6 degrees C for cells grown at 15 degrees C, respectively. All phospholipids were found in a completely fluid state at these growth temperatures. From a comparison between the phospholipids and total lipids from pellicles of cells grown at 39 degrees C, a triterpenoid alcohol, tetrahymanol, caused the transition temperature to increase. The alignment of tetrahymanol in membranes was examined with pellicle'a total lipid oriented in a sample holder.     

Functional models for growth and food consumption of Atlantic salmon parr, Salmo salar, from a Norwegian river

1. The chief objectives were to analyse and model experimental data for maximum growth and food consumption of Atlantic salmon parr (Salmo salar) collected from a cold glacier fed river in western Norway. The growth and feeding models were also applied to groups of Atlantic salmon growing and feeding at rates below the maximum. The growth models were validated by comparing their predictions with observed growth in the river supplying the experimental fish.
2. Two different models were fitted, one originally developed for British salmon and the other based on a model for bacterial growth. Both gave estimates for optimum temperature for growth at 18–19 °C, somewhat higher than for Atlantic salmon from Britain. Higher optimal temperature for growth in salmon from a cold Norwegian river than from British rivers does not concur with predictions from the thermal adaptation hypothesis.
3. Model parameter estimates differed among growth groups in that the lower critical temperature for growth increased from fast to slow growing individuals. In contrast to findings for brown trout (Salmo trutta), the optimum temperature for growth did not decrease with decreasing levels of food consumption.
4. A new and simple model showed that food consumption (expressed in energy terms) peaked at 19.5–19.8 °C, which is similar to the optimal temperature for growth. Feeding began at a temperature 1.5 °C below the lower temperature for growth and ended about 1 °C above the maximum temperature for growth. Model parameter estimates for consumption differed among growth groups in a manner similar to the growth models. Maximum consumption was lower for Atlantic salmon than for brown trout, except at temperatures above 18 °C.
5. By combining the growth and food consumption models, growth efficiency was estimated and reached a maximum at about 14 °C for fast growing individuals, increasing to nearly 17 °C for slow growing ones, although it was lower overall for the latter group. Efficiency also declined with increasing fish size. Growth efficiency was generally higher for Atlantic salmon than for brown trout, particularly at high temperature.     

Temperature dependence of growth and membrane-bound activities of Chloroflexus aurantiacus energy metabolism

The temperature dependence of various activities related to the energy metabolism of isolated membranes and whole cells of the thermophilic bacterium Chloroflexus aurantiacus was determined after phototrophic growth at either 40, 50, or 60 degrees C. The data obtained were expressed by use of Arrhenius plots. Maximum activities were determined at about 65 degrees C for succinate 2,4-dichlorophenol-indophenol reductase as well as NADH oxidase and at about 70 degrees C for Mg-ATPase and for light-induced proton extrusion by cells. Activation energies for Mg-ATPase and light-induced proton extrusion were about 40 kJ mol-1 from 30 degrees C to about 50 degrees C and they increased significantly at higher temperatures. Essentially the same dependency was detectable with NADH oxidase, except for an increase in activation energy below 41 degrees C. All of these responses were independent of growth temperature. Succinate-2,4-dichlorophenol-indophenol reductase showed a change in activation energy around 41 degrees C only with cells grown at 60 degrees C. Differences in the responses of cells grown at different temperatures were identified on the basis of changes from sigmoidal to hyperbolic kinetics for light saturation of proton extrusion. Moreover, the thermostability of proton extrusion was maximal when assayed at the corresponding growth temperatures. In any case, thermostability was lowest at the 65 and 68 degrees C assay temperatures. Differential scanning calorimetry with membranes revealed irreversible heat uptake from about 60 to 72 degrees C. The results are discussed in light of the activation energy for the specific growth rate, which is lowest at temperatures from 40 degrees C to the optimum at 60 degrees C.     

Effects of temperature and food quality on life-history parameters in Parameletus chelifer and P. minor (Ephemeroptera): a laboratory study

SUMMARY. 1. Growth rate of Parameletus minor was greatest between 10.8 and 19.8°C, survival rate peaked at 5.9°C, developmental time was shortest at 14.6°C, and adult size and fecundity reached maximum values between 5.9 and 10.8°C. Growth rate of P. chelifer was greatest between 14.6 and 19.8°C, survival rate peaked at 5.9°C, and developmental time was shortest at 14.6°C. A large adult size was found at 10.8°C, and highest fecundity between 10.8 and 14.6°C.
2. Food quality significantly affected growth rate, developmental time, adult size and fecundity of both species. Both P. chelifer and P minor attained highest growth rate, largest adult size and highest fecundity when the C/N ratio of food was 5.95. Developmental time was shortest at a C/N ratio between 5.95 and 12.8.
3. Nymphs of P. chelifer had a higher temperature 'optimum' for growth than nymphs of P. minor . Growth rate of nymphs of P. chelifer reared on detritus from a seasonal stream (C/N ratio 12.8) was about 3 times that of nymphs reared on detritus from a river margin (C/N ratio 20.9). The corresponding growth rate difference for nymphs of P. minor was only about 1.5.
4. When all life-history parameters are taken into consideration, P. chelifer had a higher temperature 'optimum' than P. minor .     

Energetics of Bacillus stearothermophilus growth: molar growth yield and temperature effects on growth efficiency.

The major growth yield of a prototrophic strain of Bacillus stearothermophilus under aerobic conditions on salts medium containing ammonium nitrate as the nitrogen source and glucose or succinate as the carbon source was maximal at the lowest growth temperature employed and decreased steadily as the temperature was raised. The temperature optima for growth yield and for growth rate were thus different. The molar growth yield values of the thermophile, especially at the lower growth temperatures, were similar to those reported for aerobically grown mesophilic bacteria, both on glucose and on succinate. At the higher growth temperatures, a lower proportion of glucose carbon was incorporated into cells and a correspondingly greater proportion was left incompletely utilized in the medium, mostly as acetate. This suggests a greater inefficiency in the coordination of the nonoxidative and oxidative phases of glucose metabolism at the gigher temperatures. Another factor causing a decreased cell yield at higher temperatures was possibly an uncoupling of energy production from respiration. The rates of respiration by intact cells of the thermophile on glucose and on succinate followed the Arrhenius relationship from 55 C to 20 C, which is some 20 C below the minimal growth temperature of the organism. The Arrhenius constant was 17.1 kcal/mol for glucose oxidation and 13.5 kcal/mol for succinate oxidation. These results are comparable to those reported for some mesophiles, and they suggest that the inability of the thermophile to grow at temperatures below about 41 C is not due to an abnormally high temperature coefficient for the uptake and oxidation of the carbon source.     

Isolation and identification of an allelopathic substance from peel of Citrus junos

The inhibitory effect of Citrus junos peel on plant growth using lettuce (Lactuca sativa L.) as a bioassay material was investigated, since the powder of the peel had been found to inhibit growth of weeds. Basic, neutral and acidic fractions were separated from the aqueous fraction obtained from the methanol extract of C. junos peel. All fractions inhibited the growth of lettuce seedlings, but by far the greatest inhibition was observed with the neutral fraction. Thus, the latter was further purified and an allelopathically active substance was isolated. The structure of the substance was determined from high-resolution MS and 1H and 13C NMR spectral data as abscisic acid-beta-D-glucopyranosyl ester (ABA-GE). ABA-GE inhibited hypocotyl and root growth of lettuce seedlings at concentrations greater than 0.3 microM, and the concentrations for 50% inhibition of hypocotyl and root growth were 2.3 and 1.4 microM, respectively. The effectiveness of ABA-GE on inhibition of growth and the occurrence of ABA-GE in the peel itself suggested that ABA-GE may play an important role in the allelopathic potential of C. junos peel. The peel may be potentially useful for weed management in a field setting.     

The effect of combined heat and ultrasound on multicellular tumour spheroids

The effect of combined ultrasound and heat treatments on Chinese hamster multicellular spheroids of varying size was investigated using growth rate, single cell survival and ultrastructural damage as endpoints. Ultrasonic irradiation at 37 degrees C had no effect on the growth rate of 200-730 microns spheroids. Similarly there was no effect on the growth rate of 350 microns spheroids when irradiated during a 60 min exposure to 41.5 degrees C. However, spheroids of 200-700 mm diameter showed growth delay when held at 43 degrees C for 1 h. The effect was enhanced with concomitant ultrasound irradiation but was not dependent on spheroid size. When 200 and 400 microns spheroids held at 43 degrees C for 60 min were irradiated with different ultrasonic intensities a dose-dependent decrease in surviving fraction and a dose-dependent increase in growth delay was obtained. When surviving fraction was plotted as a function of growth delay a good correlation was obtained, suggesting that the combination of heat and ultrasound irradiation does not produce cytostasis in the surviving cells of either 200 or 400 microns spheroids. At the ultrastructural level increased cytoplasmic vacuolation was the only result of ultrasonic irradiation at 37 degrees C. Exposure to 43 degrees C for 60 min was required to elicit thermal damage. This took the form of membrane evagination at the spheroid surface, vacuolation of the cytoplasm, grouping of organelles around the periphery of the nucleus, and fragmentation of the nucleolus. These effects were enhanced with concomitant ultrasonic irradiation but other features were also noted, viz. disaggregation of polyribosomes, dilation of the rough endoplasmic reticulum and blebbing of the nuclear membrane. Damage was independent of spheroid size. These results are in agreement with previous data obtained from single-cell studies. Indicating that there is a non-thermal, non-cavitational component to the cell killing in multicellular spheroids resulting from combined heat and ultrasound treatment.     

Influence of culture media and environmental factors on mycelial growth and pycnidial production of Sphaeropsis pyriputrescens

Sphaeropsis pyriputrescens, the causal agent of Sphaeropsis rot of pears and apples, is a recently described species. In this study the effects of culture media, temperature, water potential, pH and light on mycelial growth and pycnidial production of S. pyriputrescens were evaluated. Apple juice agar and pear juice agar were most suitable for mycelial growth of all six isolates tested. Cornmeal agar was not suitable for either mycelial growth or pycnidial production. The fungus grew from -3 to 25 C, with optimum growth at 20 C and no growth at 30 C. The fungus grew at water potential as low as -5.6 MPa on potassium chloride-amended potato-dextrose agar (PDA). Hyphal extension was not observed at -7.3 MPa after 10 d incubation, but growth resumed when the inoculum plugs were placed on PDA. The fungus grew at pH 3.3-6.3 and optimum growth was at pH 3.3-4.2. No mycelial growth was observed at pH above 7.2 after 10 d incubation, but growth resumed when the inoculum plugs were transferred onto PDA. Regardless of medium tested, few pycnidia formed at 20 C in the dark. Pycnidial production was enhanced significantly by fluorescent light, but continuous light appeared to reduce pycnidial production, depending on the medium. Oatmeal agar (OMA) was most suitable for production of pycnidia and conidia. Pycnidia that formed on 3 wk old OMA cultures at 20 C under 12 h light/12 h dark produced abundant conidia, and the technique is recommended for inoculum production.