Long-term stability of a biofilter treating dimethyl sulphide

 The biofiltration of dimethyl sulphide (Me₂S) and other volatile sulphur compounds results in the accumulation of the metabolite sulphuric acid in the carrier material. Regeneration of an acidified (pH 4.7), Hyphomicrobium-MS3-inoculated compost biofilter degrading Me₂S was not possible by trickling tap water (days 0–28) or a KH₂PO₄/K₂HPO₄ buffer solution (1.26 g PO^3- ₄ l^-1, pH 7) (days 29–47) over the bioreactor at a superficial liquid flow rate of 34 lm^-2 day^-1. Since the protons produced displaced nutrient cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH⁺ ₄) from the cation-exchange sites on the compost material, 95% of the SO^2- ₄ was leached as the corresponding sulphate salts and not as sulphuric acid. Concomitantly, the pH of the compost material decreased from 4.7 to 3.9 over the 47 days rinsing period. Moreover, the rinsing procedure resulted in the leaching of essential microbial nutrients from the compost material, such as NH⁺ ₄ (22.3% wash-out over the 47-day rinsing period) and PO^3- ₄ (39.3% washout over the 28-day tap-water rinsing period). However, mixing limestone powder into the Me₂S-degrading compost biofilter was a successful approach to controlling the pH in the optimal range for the inoculum Hyphomicrobium MS3 (pH 6–7). A stoichiometric neutralisation reaction (molar ratio CaCO₃/H₂SO₄=1.1) was observed between the CaCO₃ added and the metabolite of the Me₂S degradation, while high elimination capacities (above 100 g Me₂S m^-3 day^-1) were obtained over a prolonged (more than 100 days) period. Received: 1 December 1995/Received revision: 26 April 1995 Accepted: 29 April 1996     

Influence of the water content and water activity on styrene degradation by Exophiala jeanselmei in biofilters

 The performance at low water availability of styrene-degrading biofilters with the fungus Exophiala jeanselmei growing on perlite, the inert support, was investigated. E. jeanselmei degrades styrene at a water activity of 0.91–1. In biofilters, the styrene elimination capacity at a water activity of 0.91 is 5% of the maximal elimination capacity of 79 g m^-3 h^-1 (water activity 1). Application of dry air results in a rapid loss of styrene degradation activity, even at 40%–60% (w/w) water in the filter bed and at a water activity of 1. Humidification of the gas and an additional supply of water to the filter bed are necessary to maintain a high and stable styrene elimination capacity. Received: 7 August 1995 / Received revision: 29 January 1996 / Accepted: 5 February 1996     

Sulfated extracellular polysaccharide production by the halophilic cyanobacterium Aphanocapsa halophytia immobilized on light-diffusing optical fibers

 The cyanobacterium, Aphanocapsa halo-phytia MN-11, was immobilized in calcium alginate gel and coated on light-diffusing optical fibers (LDOF) for sulfated extracellular polysaccharide production. Results indicated that sulfated extracellular polysaccharide production depends on the number of immobilized cells and the light intensity. In addition, the production rate reached 116.0 mg (mg dry cells)^-1 day^-1 when the cells that were immobilized on LDOF were incubated under a light intensity of 1380 cd sr m^-2 at a cell concentration of 1.0×10⁸ cells/cm³ gel. Cells immobilized on LDOF produced about ten times more sulfated extracellular polysaccharide than those immobilized in calcium alginate beads only (11.7 mg(mg dry cells)^-1day^-1). Received: 31 March 1995/Revised last revision 12 June 1995/Accepted 26 July 1995     

Isobutyraldehyde as a competitor of the dimethyl sulfide degrading activity in biofilters

Upon inoculation with Hyphomicrobium MS3, theelimination capacity of a lab-scale biofilter for theodorant dimethyl sulfide (Me₂S) can be stronglyincreased from less than 10 to more than 35 and 1000 gm^-3d^-1 using wood bark and compost as acarrier material, respectively. However, uponsupplementation of isobutyraldehyde (IBA) as a secondgaseous substrate, sequential degradation profiles of IBAand Me₂S in physically separated sections wereobserved in the Hyphomicrobium MS3-inoculatedwood bark and compost biofilters. Contrary to this, thebiofiltration efficiency for Me₂S remainedunaffected upon the supplementation of toluene as asecond gaseous substrate. Batch experiments with theliquid Hyphomicrobium MS3 culture confirmed thecompetitive effect of IBA on the Me₂S degradingactivity: in the presence of both compounds, Hyphomicrobium MS3 preferred degradation of thecarbonyl compound. In technical terms, this means thatthe complete purification of a waste gas stream containingboth IBA and Me₂S should be performed usingsufficiently high or bistage HyphomicrobiumMS3-inoculated biofilters. Design criteria have to beconceived in this respect.     

Dolomite limits acidification of a biofilter degrading dimethyl sulphide

The applicability of dolomite particlesto control acidificationin a Hyphomicrobium MS3inoculated biofilter removingdimethyl sulphide (Me₂S) wasstudied. While direct inoculationof the dolomite particles with theliquid microbial culture was notsuccessful, start-up ofMe₂S-degradation in thebiofilter was observed when thedolomite particles were mixed with33% (wt/wt) of Hyphomicrobium MS3-inoculatedcompost or wood bark material.Under optimal conditions, anelimination capacity (EC) of 1680~g Me₂S m^-3 d^-1 wasobtained for the compost/dolomitebiofilter. Contrary to a wood barkor compost biofilter, no reductionin activity due to acidificationwas observed in these biofiltersover a 235 day period because ofthe micro environmentneutralisation of the microbialmetabolite H₂SO₄ with thecarbonate in the dolomite material.However, performance of thebiofilter decreased when themoisture content of the mixedcompost/dolomite material droppedbelow 15%. Next to this, nutrientlimitation resulted in a gradualdecrease of the EC andsupplementation of a nitrogensource was a prerequisite to obtaina long-term high EC (> 250 gMe₂S m^-3 d^-1) forMe₂S. In relation to thisnitrogen supplementation, it wasobserved that stable ECs forMe₂S were obtained when thisnutrient was dosed to the biofilterat a Me₂S-C/NH₄Cl-Nratio of about 10.Abbreviations:DW – dry weight,EC – elimination capacity,Me₂S – dimethyl sulphide,OL – organic loading rate,VS - volatile solids     

Transition rate kinetics from ethanol oxidation to glucose utilisation within a structured model of baker’s yeast

 The transition rate kinetics from ethanol oxidation to glucose utilisation, within a structured model of baker’s yeast, described previously, were experimentally identified. The shift in metabolism has been assessed through glucose pulses during batch growth on ethanol. The influence of glucose concentration (between 0.25 g l^-1 and 0.90 g l^-1) and initial biomass concentration (between 0.61 g l^-1 and 1.44 g l^-1) on the transition rate was determined. The transition rate can not be described by a first-order saturation-type kinetics with respect to glucose only. A corrective term, which takes into account biomass concentration should be included. Received: 28 April 1995/Received revision: 6 July 1995/Accepted: 22 August 1995     

Uptake of lactose and continuous lactic acid fermentation by entrapped non-growing Lactobacillus helveticus in whey permeate

 Continuous production of lactic acid from lactose has been carried out in a stirred-tank reactor with non-growing Lactobacillus helveticus entrapped in calcium alginate beads. A considerably longer operation half-life was obtained in a continuously operated reactor than in a batch-operated reactor. It is possible to simulate the action of entrapped non-growing cells on the basis of information from diffusion and kinetic experiments with suspended free cells. The simulation fit the experimental data over a broad range of substrate concentrations if the specific lactic acid production rate, q _P, was used as a variable parameter in the model. The dynamic mathematical model used is divided into three parts: the reactor model, which describes the mass balance in a continuously operated stirred-tank reactor with immobilized biomass, the mass-transfer model including both external diffusion and internal mass transfer, and the kinetic model for uptake of substrate on the basis of a Michaelis-Menten-type mechanism. From kinetic data obtained for free biomass experiments it was found, with the use of non-linear parameter estimation techniques, that the conversion rate of lactose by L. helveticus followed a Michaelis-Menten-type mechanism with K _S at half-saturation=0.22±0.01 g/l. The maximum specific lactose uptake rate for growing cells, q _S,max, varied between 4.32±0.02 g lactose g cells^-1 h^-1 and 4.89 ±0.02 g lactose g cells^-1 h^-1. The initial specific lactose uptake rate for non-growing cells, q _S,0, was found to be approximately 40% of the maximum specific lactose uptake rate for growing cells. Received: 4 October 1995/Received last revision: 23 April 1996/Accepted: 29 April 1996     

Shake-flask culture of Laccaria laccata,an ectomycorrhizal basidiomycete

 Large-scale exploitation of the potential benefits of ectomycorrhizal fungi in improving plantation yields means that fermentation techniques for these fungi will be required. Starting with a base performance on a rich, complex medium, the effect of variations in some physicochemical culture parameters on biomass yield was studied. It was possible to reduce the amount of phosphate salts (to 1/9th) and other ingredients (to 1/3rd) in the medium. A shaking speed of either 100 rpm or 200 rpm in an orbital incubator was satisfactory and biomass yield responded to an increase in carbon substrate (glucose, from 10 g l^-1 and 20 g l^-1) though Y _x/s declined. An increase in inoculum size shortened culture time but decreased biomass yield. The upper limit of the incubation temperature was between 25°C and 30°C. Biomass yields were about 12 g l^-1 dry weight (Y _x/s=0.63) when 20 g l^-1 glucose was supplied, and about 7 g l^-1 (Y _x/s=0.74) when 10 g l^-1 glucose was supplied. Received: 9 October 1995/Accepted: 4 December 1995     

Picophytoplankton biomass, community structure and productivity in the Great Astrolabe Lagoon, Fiji

 Phytoplankton biomass, community structure and productivity of the Great Astrolabe lagoon and surrounding ocean were studied using measurements of chlorophyll concentration and carbon uptake. The contribution of picophytoplankton to biomass, productivity and community structure was estimated by size fractionation, ¹⁴C-incubation and flow cytometry analysis. Picoplankton red fluorescence was demonstrated to be a proxy for chlorophyll <3 μm. Consequently, the percentage contribution to chl a<3 μm from each picoplankton group could be calculated using regression estimated values of ψ _i (fg chl a per unit of red fluorescence). In the lagoon, average chlorophyll concentration was 0.8 mg m^-3 with 45% of phytoplankton <3 μm. Primary production reached 1.3 g C m^-2 day^-1 with 53% due to phytoplankton <3 μm. Synechococcus was the most abundant group at all stations, followed by Prochlorococcus and picoeukaryotes. At all stations, Prochlorococcus represented less than 4% of the chl a <3 μm, Synechococcus between 85 and 95%, and Picoeukaryotes between 5 and 10%. In the upper 40 m of surrounding oceanic waters, phytoplankton biomass was dominated by the >3 μm size fraction. In deeper water, the <1 μm size fraction dominated. Prochlorococcus was the most abundant picoplankton group and their contributions to the chlorophyll a<3 μm were close to that of the picoeukaryotes (50% each). Accepted: 27 May 1999     

Effect of ferrous iron concentration on the catalytic activity of immobilized cells of Thiobacillus ferrooxidans

 The kinetics of continuous oxidation of ferrous iron by immobilized cells of Thiobacillus ferrooxidans was studied in a packed-bed bioreactor. Polyurethane foam biomass support particles were used as carriers for cell immobilization. Effects of ferrous iron concentration and its volumetric loading on the kinetics of the reaction were investigated. Media containing different concentrations of ferrous iron in the range 5–20 kg m^-3 were tested. For each medium the kinetics of the reaction at different volumetric loadings of ferrous iron, at a constant temperature of 30^°C, were determined. With media containing 5 kg m^-3 and 10 kg m^-3 Fe²⁺, the fastest oxidation rates of 34.25 kg m^-3 h^-1 and 32 kg m^-3 h^-1 were achieved at a dilution rate of around 6 h^-1, which represents a residence time of 10 min. Employing a higher concentration of ferrous iron (20 kg m^-3) in the medium resulted in lower oxidation rates, with a maximum value of 10 kg m^-3 h^-1, indicating an inhibitory effect of ferrous iron on growth and activity of T. ferrooxidans. The reliable performance of the bioreactor during the course of the experiments confirmed the suitability of polyurethane foam biomass support particles as carriers for T. ferrooxidans immobilization. Received: 5 December 1995/Received revision: 21 April 1996/Accepted: 29 April 1996     

Microbial treatment of a styrene-contaminated air stream in a biofilter with high elimination capacities

A styrene-utilizing mixed microbial culture was isolated and utilized in a biofilter for the biological treatment of a contaminated air stream. Biofilter media consisted of composted wood bark and yard waste. The biofilters were acclimated at 120 s residence time and further evaluated at 60 and 30 s gas residence times. The biofilters received organic loading rates of up to 350 g/m³ h. The styrene volumetric removal rate was a function of the organic loading rate and increased with increasing loading rates. Average volumetric removal rates of 69–118 g/m³ h observed in our studies were higher than reported values for styrene biofilters. Average styrene removal efficiencies ranged from 65% to 75% (maximum 100%). Axial analysis of styrene concentration along the column indicated that the bulk of the styrene removal occurred in the first section of the biofilter. Analyses of the media indicated that the moisture content of the first section (50–55% w/w) was significantly lower than in the second and third sections (65–70% w/w). The pressure drops across the biofilter were low due to the high concentration of large media particles. The total pressure drops were 1–3, 4–6, and 10–16 mm for the 120-, 60-, and 30-s residence time periods, respectively. Journal of Industrial Microbiology & Biotechnology (2001) 26, 196–202. Received 04 March 2000/ Accepted in revised form 25 January 2001     

Degradation of pyrene by Mycobacterium flavescens

 A strain of Mycobacterium flavescens was isolated from polluted sediments. It was capable of utilizing pyrene as a sole source of carbon and energy. When pyrene was supplied as a suspension at 50 μg/ml, the generation time was 9.6 h and the rate of pyrene utilization was 0.56 μg ml^-1 day^-1. In addition to pyrene, the strain could mineralize phenanthrene (17.7%) and fluoranthene (17.9%), but failed to mineralize naphthalene, chrysene, anthracene, fluorene, acenaphthene and benzo[a]pyrene, as determined by recovery of radiolabeled CO₂ in incubations conducted for 2 weeks under growth conditions. Metabolites produced during growth on pyrene were detected and characterized by HPLC and GC-MS. The product of initial ring oxidation, 4,5-dihydroxy-4,5-dihydropyrene was identified, as well as ring-fission products including 4-phenanthroic acid, phthalic acid, and 4,5-phenanthrenedioic acid. Received: 3 October 1995/Received last revision: 1 April 1996/Accepted: 15 April 1996     

Cell-free extract(s) of Pseudomonas putida catalyzes the conversion of cyanides,cyanates, thiocyanates,formamide, and cyanide-containing mine waters into ammonia

 Our isolate, Pseudomonas putida, is known to be capable of utilizing cyanides as the sole source of carbon (C) and nitrogen (N) both in the form of free cells and cells immobilized in calcium alginate. In the present study, the cell-free extract(s) were prepared from the cells of P. putida grown in the presence of sodium cyanide. The ability of enzyme(s) to convert cyanides, cyanates, thiocyanates, formamide and cyanide-containing mine waters into ammonia (NH₃) was studied at pH 7.5 and pH 9.5. The kinetic analysis of cyanide and formamide conversion into NH₃ at pH 7.5 and pH 9.5 by the cell-free extract(s) of P. putida was also studied. The K _m and V _max values for cyanide/formamide were found to be 4.3/8 mM and 142/227 μmol NH₃ released mg protein^-1 min^-1 respectively at pH 7.5 and 5/16.67 mM and 181/434 μmol NH₃ released mg protein^-1 h^-1 respectively at pH 9.5. The study thus concludes that the cell-free extract(s) of P. putida is able to metabolize not only cyanides, cyanates, thiocyanates, and formamide but also cyanide-containing mine waters to NH₃. Received: 10 April 1995/Received revision: 24 July 1995/Accepted: 22 August 1995     

Nitrogen and energy requirements of the short-tailed fruit bat (Carollia perspicillata): fruit bats are not nitrogen constrained

 Nitrogen (N) and energy (E) requirements were measured in adult Carollia perspicillata which were fed on four experimental diets. Bats ate 1.3–1.8 times their body mass ⋅ day^-1 and ingested 1339.5–1941.4 kJ ⋅ kg^-0.75 ⋅ day^-1. Despite a rapid transit time, dry matter digestibility and metabolizable E coefficient were high (83.3% and 82.4%, respectively), but true N digestibility was low (67.0%). Mass change was not correlated with E intake, indicating that bats adjusted their metabolic rate to maintain constant mass. Bats were able to maintain constant mass with digestible E intake as low as 1168.7 kJ ⋅ kg^-0.75 ⋅ day^-1 or 58.6 kJ ⋅ . Metabolic fecal N and endogenous urinary N losses were 0.87 mg N ⋅ g^-1 dry matter intake and 172.5 mg N ⋅ kg^-0.75 ⋅ day^-1, respectively, and bats required 442 mg N ⋅ kg^-0.75 ⋅ day^-1 (total nitrogen) or 292.8 mg N ⋅ kg^-0.75 ⋅ day^-1 (truly digestible nitrogen) for N balance. Based on E and N requirements and digestibilities, it was calculated that non-reproductive fruit bats were able to meet their N requirements without resorting to folivory and without over-ingesting energy. It was demonstrated that low metabolic fecal requirements allowed bats to survive on low-N diets. Accepted: 23 June 1996     

Complete degradation of tetrachloroethene by combining anaerobic dechlorinating and aerobic methanotrophic enrichment cultures

 Degradation of tetrachloroethene (perchloroethylene, PCE) was investigated by combining the metabolic abilities of anaerobic bacteria, capable of reductive dechlorination of PCE, with those of aerobic methanotrophic bacteria, capable of co-metabolic degradation of the less-chlorinated ethenes formed by reductive dechlorination of PCE. Anaerobic communities reductively dechlorinating PCE, trichloroethene (TCE) and dichloroethenes were enriched from various sources. The maximum rates of dechlorination observed for various chloroethenes in these batch enrichments were: PCE to TCE (341 μmol l^-1 day^-1), TCE to cis-dichloroethene (159 μmol l^-1 day^-1), cis-dichloroethene to chloroethene (99 μmol l^-1 day^-1) and trans-dichloroethene to chloroethene (22 μmol l^-1 day^-1). A mixture of these enrichments was inoculated into an anoxic fixed-bed upflow column. In this column PCE was converted mainly into cis-1, 2-dichloroethene, small amounts of TCE and chloroethene, and chloride. Enrichments of aerobic methanotrophic bacteria were grown in an oxic fixed-bed downflow column. Less-chlorinated ethenes, formed in the anoxic column, were further metabolized in this oxic methanotrophic column. On the basis of analysis of chloride production and the disappearance of chlorinated ethenes it was demonstrated that complete degradation of PCE was possible by combining these two columns. Operation of the two-column system under various process conditions indicated that the sensitivity of the methanotrophic bacteria to chlorinated intermediates represented the bottle-neck in the sequential anoxic/oxic degradation process of PCE. Received: 24 October 1994 / Received revision: 20 January 1995 / Accepted: 23 January 1995     

Toluene degradation in a polyurethane biofilter at high loading

In the present study, toluene elimination in the polyurethane (PU) biofilter during long-term (145 day) operation was characterized, and assessed the effects of changing the inlet loading and space velocity (SV). A very high elimination capacity of 3.7 kg·m⁻³·h⁻¹ was obtained at an inlet loading of 4.0 kg·m^–3·h⁻¹ (inlet toluene concentration of 900 ppmv at a SV of 1,040 h⁻¹). Backwashing with irrigation and compressed air allowed maintenance of a pressure drop of < 80 mm H₂O·m⁻¹-filter at an SV of 830 h⁻¹ and an elimination efficiency of > 90% during the 145 day of operation. In conclusion, the PU biofilter can overcome the problems of clogging caused by excess biomass growth and of low treatment capacities of conventional biofilters.     

Toluene vapour removal in a laboratory-scale biofilter

A bench-scale biofilter with a 0.5-m high filter bed, inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, was used to study toluene removal from a synthetic waste air stream. Different sets of continuous tests were conducted at influent toluene concentrations ranging over 0.1–4.0 g m⁻³ and at superficial gas velocities ranging over 17.8–255 m h⁻¹. The maximum volumetric toluene removal rate for the biofilter (242 g m⁻³ h⁻¹) was obtained at a superficial gas velocity of 127.5 m h⁻¹ (corresponding to a residence time of 28 s) and a toluene inlet concentration of 4.0 g m⁻³. Under these operating conditions, toluene removal efficiency was only 0.238, which suggested that effective operation required higher residence times. Removal efficiencies higher than 0.9 were achieved at organic loads less than 113.7 g m⁻³ h⁻¹. A macro-kinetic study, performed using concentration profiles along the bioreactor, revealed this process was limited by diffusion at organic loads less than 100 g m⁻³ h⁻¹ and by biological reaction beyond this threshold. Received: 10 October 1999 / Received revision: 15 February 2000 / Accepted: 18 February 2000     

Effect of temperature and various nitrogen sources on L(+)-lactic acid production by Lactobacillus casei

 Two homofermentative strains, Lactobacillus casei NRRL B-441 and Lactobacillus casei subsp. rhamnosus NRRL B-445 were selected for further study from 17 lactic acid bacterial strains screened for lactic acid production. The effect of temperature on lactic acid production with the selected strains was investigated by adapting both strains to four different temperatures. The production of L(+)-lactic acid by both strains was most efficient at 37°C, although with L. casei the highest lactic acid concentration was obtained at 41°C. The maximal volumetric productivity with L. casei was 4.1 g l^-1 h^-1 and with L. casei subsp. rhamnosus 3.5 g l^-1 h^-1. The composition of the medium was studied in order to replace the costly yeast extract with less expensive sources of nitrogen and amino acids. From 11 different nitrogen sources investigated at 37°C, barley malt sprouts (88 g l^-1 lactic acid in 66 h) and grass extract (74 g l^-1 lactic acid in 73 h) were the best economic alternatives. The effect of different combinations of yeast extract, peptone and malt sprouts was further studied by using statistical experimental design, and an empirical second-order polynomial model was constructed on the basis of the results. With the right combination most of the yeast extract could be substituted by barley malt sprouts for efficient lactic acid production. A method for extraction of nutrients and growth factors from malt sprouts is also described. Received: 25 September 1995/Accepted: 24 October 1995     

Use of an industrial effluent as a carbon source for denitrification of a high-strength wastewater

Denitrification of a high-strength synthetic wastewater (150 g NO^- ₃ l^-1) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand l^-1). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of 9.54 g NO^- ₃ l^-1 day^-1 (2.19 g N as NO^- ₃ l^-1 day^-1) with good specific reduction rates: 32.6 mg and 35.2 mg N as NO _x  g volatile suspended solids h^-1, calculated on a single day, for the two-step and the one-step process respectively. Dissimilatory nitrate reduction to ammonium did not occur, even in the one-step process. Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996     

Genetic variation for in vitro sesame pollen germination and tube growth

  In vitro pollen germination and tube length studies are valuable in elucidating mechanisms (germination capacity and rate, tube growth rate) possibly associated with genetic differences in male transmission. On each of two collection dates, the percentage germination and tube length of the binucleate pollen grains from five diverse sesame (Sesamum indicum L.) genotypes were determined at eight times (30, 60, 90, 120, 150, 180, 240, 300 min) after inoculation on a semisolid medium containing 10% (100 g l^-1) sucrose (C₁₂H₂₂O₁₁), 0.4% (4 g l^-1) purified agar (Fisher Lot 914409), 0.1% (1 g l^-1) calcium nitrate [Ca(NO₃)₂ ⋅ 4H₂O] and 0.01% (100 mg l^-1) boric acid (H₃BO₃). Before heating, the pH of the medium was adjusted to 7.0 with a 0.1 N potassium hydroxide (KOH) solution. Over the five genotypes, 5% germination was found 30 min after inoculation and a maximum of 37% germination 120 min after inoculation with no significant changes thereafter. As indicated by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which germination was initiated and maximum germination attained. Over all five genotypes, the tube length was 91 μm 30 min after inoculation, reaching a maximum of 1000 μm 300 min after inoculation. As shown by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which tube length was observed and the maximum tube length was attained. Little or no relationship between percent germination and tube length was observed among the genotypes. For both percent germination and tube length, the statistical significance of collection date and its interactions with genotype and time after inoculation indicated that environment in the form of collection date was also an influencing factor. These results indicated that genetic differences among genotypes were present for in vitro germination capacity, germination rate and tube growth rate and that these factors singly or in combination could alter male transmission of genetic elements. Received: 5 February 1997 / Accepted: 23 June 1997