Comparison of natural and artificial epidemics of take-all in sequences of winter wheat crops

Winter wheat was grown for six successive years (Expt 1) and for three successive years (Expt 2) in field experiments on different soil types. Artificial inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici cultured on autoclaved oat grains) was incorporated in the soil of some of the plots just before, or at, sowing of the first winter wheat crop. Expt 1 tested the incorporation of similar amounts of inoculum (212 kg ha^-1) at different depths. Expt 2 tested different amounts of inoculum at the same, shallow depth. Early sowing (September), late sowing (October) and spring inoculation were additional treatments, applied to the first crop only, in Expt 2. Seasonal factors apart, the disease outcome in the first year after inoculation depended on amounts and placement of applied inoculum, as well as date of sowing. Deeper inoculum resulted in less disease (Expt 1). Severe take-all was produced in Expt 2 by incorporating inoculum shallowly in sufficient quantities (400 kg ha^-1 or more). Less inoculum (200 kg ha^-1) generated less disease, especially in earlier-sown plots. Differences in disease amongst inoculum treatments were greatest in the first year and diminished subsequently, particularly where sowing had been early in the first year. In Expt 1, where first crops exposed to artificial inoculum developed moderate-to-severe disease, disease in subsequent second and/or third crops was less. In the fourth crop a second peak of disease occurred, coinciding with a first peak in sequences without added inoculum. Take-all decline (TAD) appeared to be expressed in all sequences thereafter. In Expt 2 in sequences without added inoculum, TAD occurred after a peak of disease in the second crop. Where 400 kg ha^-1 or more of inoculum were added, disease was severe in the first year and decreased progressively in successive years. Disease was less patchy in plots that received artificial inoculum. However, it remains uncertain mat severe disease caused by artificial inoculation achieved an early onset of true TAD. The infectivity of the top 12 cm of soil in the first 3 yr of Expt 1, determined by bioassay, depended on the depth of added inoculum and amount of disease in subsequent crops. However, at the time of the naturally occurring peak of disease severity (in either inoculated or non-inoculated plots) it did not predict either disease or TAD. Differences and similarities amongst epidemics developing naturally and those developing from different amounts and placement of applied inoculum have been revealed. The epidemiological implications of adding inoculum and the potential value of artificially-created epidemics of take-all in field trials are discussed.     

Competition between two somatic serotypes of Rhizobium japonicum used as double-strain inocula in varying proportions

Summary The nodulation response of soybeans (Glycine max, Mukden variety) to single-strain inocula was related to the density of suspensions. The competition between two different somatic serotypes, represented by the strains D 216 and D 344, was also found to be generally related to the ratio of inoculum strain cells in suspensions, but the strain D 216 was more successful in the root-nodule formation, accounting for 100-80 percent of the serotyped root-nodules when the ratio between cells of the strains D 216 and D 344 varied between 3:5 and 1:60.This investigation forms part of a contribution prepared by the Czechoslovak National Committee for the International Biological Programme (Section PP: Production Processes).     

Direct Delivery of Inoculum to Shoot Tissue Interferes with Genotypic Resistance to Ralstonia solanacearum in Tomato Seedlings

Employing known susceptible and resistant genotypes and pure bacterial inoculum (0.1 OD; 10⁸ CFU/ml^?1), five different inoculation methods were tried to assess the response of tomato genotypes to Ralstonia solanacearum. This included seed‐soaking inoculation, seed‐sowing followed by inoculum drenching, or at 2‐week stage through petiole‐excision inoculation, soaking of planting medium with inoculum either directly or after imparting seedling root‐injury. Seed‐based inoculations or mere inoculum drenching at 2 weeks did not induce much disease in seedlings. Petiole inoculation induced 90–100% mortality in susceptible checks but also 50–60% mortality in normally resistant genotypes within 7–10 days. Root‐injury inoculation at 2‐week seedling stage appeared the best for early and clearer distinction between resistant and susceptible lines. The observations suggest a role played by the root system in governing genotypic resistance to the pathogen. Direct shoot inoculation is to be adopted only for selecting highly resistant lines or to thin down segregating populations during resistance breeding.     

Competition Alters Temporal Dynamics of Sporulation in the Wheat Stem Rust Fungus

To investigate the effects of competition on the timing of pathogen reproduction, urediniospores of two strains of Puccinia graminis f.sp. tritici (SR22 and SR41) were inoculated onto leaves of wheat seedlings singly and in 1 : 1 mixture at three inoculum densities. On randomly sampled leaves, uredinia were counted 9 days after inoculation and urediniospores were collected and quantified every other day from the seventh to the 29th day after inoculation. Increases in inoculum density resulted in progressively smaller increases in uredinial numbers. However, total urediniospore production per leaf was not significantly affected by inoculum, and hence uredinial, density over a range of approximately 10-300 uredinia on the leaf. Total urediniospore production per uredinium generally decreased with increasing inoculum or uredinial density. At high densities, sporulation per uredinium peaked earlier in the sporulation period, had a less distinct peak, and dropped off earlier than for the lower densities. Logistic model fits to cumulative sporulation curves over time revealed that strain SR41 had a greater epidemic rate parameter (r) than SR22 at low and intermediate inoculum or uredinial densities, while SR22 had a higher r-value than SR41 at high density. Both strains also exhibited greater r-values in the presence of the other strain than when alone. Results suggest that strains may have different ecological strategies in their timing of reproduction, and that both intra- and interstrain competition can have complex effects on the temporal dynamics of sporulation in pathogen strains.     

Effect of different potting systems; inoculation time; nematode density and sources of cereal cyst nematode (Heterodera filipjevi) on juvenile penetration into wheat root system

Investigations were designed to optimize testing systems for screening wheat breeding lines for resistance to Heterodera filipjevi. The effects of: 1) plant potting systems 2) inoculum level and time of inoculation 3) and type of inoculum of H. filipjevi on detection accuracy were examined in growth chamber experiments in Turkey. The rate of nematode penetration in the highly susceptible variety Bezostaya was used as the base measurement of efficacy. The results showed that the highest level of penetration coupled with high level of germination was obtained in plastic tubes (13 cm long x 3 cm in diam.) when compared to both small flower pots (400 cm3) and smaller plastic tubes (10.2 cm long x 0.8 cm in diam.). The highest rate of nematode penetration into wheat root system was obtained by inoculating the seedlings with 1000 J2 per plant. However, inoculation with 200 J2 at sowing or 200 J2 at sowing plus an additional 200 J2 after germination improved percent penetration when compared to inoculation with 600 or 1000 J2/plant at sowing. The test on the optimum form of inoculum showed that inoculating the seedling with J2's gave the highest rate of nematode penetration over inoculum with eggs or cysts. The results of these experiments demonstrated that screening wheat for resistance can be optimized by raising the seedlings in plastic tubes and inoculating them with 400 J2.     

The effect of frit fly (Oscinella frit) control measures on the establishment of seedling ryegrass (Lolium spp.)

In four experiments from 1981 to 1983 August-sown perennial (Lolium perenne) and Italian (L. multiflorum) ryegrass were exposed to frit fly attack by oviposition on the seedlings. Responses to pesticide treatment were detected at autumn harvests. Even at low sowing rates pesticide application did not ultimately establish a better sward and, owing to a tendency towards spring reversal of autumn yield responses, even temporary returns were negligible. As frit fly numbers were unusually low the autumn response to pesticide was sufficient to suggest that frit fly is always likely to be an influential factor in ryegrass sown in early August in this area. Later sowings are less likely to be affected. The yield response was related to the numbers of adult flies present 2–7 wk after sowing. Neither grass species was consistently more affected than the other. Additional seed (compared with a sowing rate below normal commercial rates) and the inclusion of fertiliser at sowing also gave only small temporary returns and failed to establish a better sward. It is suggested that routine protection against frit fly attack is of at least equal value to the other two variables in an early August sowing.     

Identification ofRhizobium strains and evaluation of their competitiveness

Six strains ofRhizobium leguminosarum bv.viciœ, three strains ofBradyrhizobium japonicum and three strains ofRhizobium fredii were evaluated by the polymerase chain reaction (PCR). The possibility of identification of individual rhizobial strains and the way of product analysis were verified. The result of amplifications proved rich spectra along the whole length scale. Numerous identical bands could be found in related strains. Verification of the expected identity of some strains confirmed the applicability of this method for identification of individual bacterial strains of generaRhizobium andBradyrhizobium. Furthermore, competitiveness of two strains ofR. leguminosarum bv.viciœ against the native rhizobial population was evaluated in a pot experiment. When using PCR as the identification method, the presence of the strains in host plant's nodules was ascertained after inoculation by different rates of inoculum strains. With increasing the inoculum rate, the presence of inoculum strains in pea nodules also increased. On the basis of mathematical models by Amarger and Lobreu the competitiveness of the mentioned strains was estimated at certain inoculum rates. Both tested strains displayed a higher competitiveness than native rhizobia in the soil used. As they are also effective N₂ fixators (one strain being HUP⁺), one may expect successful field inoculations with them.     

Inoculum Density and Population Dynamics of Suppressive and PathogenicStreptomycesStrains and Their Relationship to Biological Control of Potato Scab

SeveralStreptomycesstrains are capable of suppressing potato scab caused byStreptomyces scabies.Although these strains have been successful in the biocontrol of potato scab in the field, little is known about how populations of pathogenicStreptomycesin the potato rhizosphere are influenced by inoculation of the suppressive strains. The effects of inoculum densities of pathogenic and suppressiveStreptomycesstrains on their respective populations on roots and in rhizosphere soil were examined during the growing season. The relationships between inoculum density or rhizosphere population densities and disease severity were also investigated. Populations of suppressiveStreptomycesstrain 93 increased significantly on roots with increasing inoculum dose. At its highest inoculum dose, the suppressive strain reached a population density greater than 10⁶CFU/g root 14 weeks after planting. The ability of the suppressive strain to increase its populations with increasing inoculum density was hindered at high inoculum doses of the pathogen, suggesting that density-dependent competitive interactions may be occurring between the two antagonists. Strain 93 was most effective at preventing scab early in the growing season (8 weeks after planting), when tubers were most susceptible to the scab disease. Population densities of the suppressive strain in soil were more highly negatively correlated with scab severity than were populations on roots, suggesting that rhizosphere soil rather than potato roots may be the primary source of inoculum of the suppressive strain for tubers.     

Persistence of introduced Bradyrhizobium japonicum strains in forming nodules in subsequent years after inoculation in Wisconsin soils

Nodulation of soybeans by indigenous and inoculum strains of Bradyrhizobium japonicum was studied in field experiments in Wisconsin from 1983 to 86. Aqueous suspensions of bacteria were applied to seeds at the time of planting at levels of 7?×?10(7)-10(10) bacteria per 2.5-cm row. The predominant indigenous serogroup was 123 in these soils. Six different inoculum strains were used (two from serocluster 123, two from serogroup 110, and one each from serogroups 122 and C1). Nodule occupants were identified using spontaneous antibiotic-resistant mutations in the inoculum strains, phage typing, and serotyping. In the 1983 experiment, the majority of nodules were formed by the inoculum strains in almost all cases (up to 100% in some cases), in two different soils containing 3.5?×?10(5) indigenous B. japonicum per gram. After 2 years without inoculation at the same two site, the inoculum strains did not form many nodules on uninoculated soybeans (less than 10% in most cases; less than 30% in all cases). In inoculation experiments carried out in 1985 and 1986, four inoculum strains were used (3 members of 123 serocluster and USDA 110str); inocula containing 10(8) bacteria per 2.5-cm row formed less than42%ofthe nodules in soils containing 1?×?10(4)-4?×?10(4)B. japonicum per gram. The major conclusions are (i) the success of inoculation in Midwestern U.S. soils is highly variable, even with members of the (highly competitive) 123 serocluster, and (ii) successful inoculation in 1 year in a Wisconsin soil does not ensure that the inoculated strain will persist in forming nodules in that field in subsequent years without further inoculation. Key words: Bradyrhizobium japonicum, strain persistence, field trials.     

Responses of soil microbial catabolic diversity to arbuscular mycorrhizal inoculation and soil disinfection

Although it is usually admitted that arbuscular mycorrhizal (AM) fungi are key components in soil bio-functioning, little is known on the response of microbial functional diversity to AM inoculation. The aims of the present study were to determine the influence of Glomus intraradices inoculum densities on plant growth and soil microflora functional diversity in autoclaved soil or non-disinfected soil. Microbial diversity of soil treatments was assessed by measuring the patterns of in situ catabolic potential of microbial communities. The soil disinfection increased sorghum growth, but lowered catabolic evenness (4.8) compared to that recorded in the non-disinfected soil (6.5). G. intraradices inoculation induced a higher plant growth in the autoclaved soil than in the non-disinfected soil. This AM effect was positively related to inoculum density. Catabolic evenness and richness were positively correlated with the number of inoculated AM propagules in the autoclaved soil, but negatively correlated in the non-disinfected soil. In addition, after soil disinfection and AM inoculation, these microbial functionality indicators had higher values than in the autoclaved or in the non-disinfected soil without AM inoculation. These results are discussed in relation to the ecological influence of AM inoculation, with selected fungal strains and their associated microflora on native soil microbial activity.     

Inoculation of pea by application of Rhizobium in the planting furrow

Summary Selected streptomycin resistant strains ofRhizobium leguminosarum suspended in nutrient broth were added to the planting furrow immediately before the sowing of pea. The nodule occupancy by a strain isolated from Risø soil (Risø la) was increased from 74 to 90%, when the inoculum rate was increased from 3.7×10⁶ to 3.7×10⁸ cells per cm row. The experimental soil contained 10³ to 10⁴ cells ofR. leguminosarum per gram. An almost inefficient strain isolated from Risø soil (SV10) was less competitive with respect to nodulation on two pea cultivars than an efficient Risø strain (SV15) and an efficient non-Risø strain (R1045). The nodule occupancy by the introduced strains varied between pea cultivars.Irrespective of the generally high nodulation by the efficient strains introduced to the soil, the pea seed yield, compared to pea nodulated by the indigenous population, was not significantly increased. Neither were two commercial inoculants, applied in rates corresponding to 3 times the recommended rate, able to increase the yield. This suggests that the indigenous populations ofR. leguminosarum were sufficient in number and nitrogen fixing capacity to ensure an optimal pea crop. However, some inoculation treatments slightly increased the seed N concentration and total N accumulation, indicating that it may be possible to select or develop bacterial strains that may increase the yield.     

Design of a novel alkaliphilic bacterial system for triggering biopolymer gels

The use of microorganisms to trigger a delayed gelling reaction with curdlan biopolymer gelant was evaluated. The gel-triggering bacteria were strict alkaliphiles isolated from a soda lake. Using the alkaliphilic isolates to trigger gel formation, gelation time was inversely proportional to inoculum concentration and could be delayed up to 12 days after inoculation. The microbially triggered polymer system was injected into cores and then gelled in situ. Treatment of cores with the system decreased brine permeability by two to four orders of magnitude. Individual strains of the alkaliphiles had distinct effects on the polymer system, with respect to both gelling time and permanence of the polymer gel. These strain-specific traits may be exploited to design gelled polymer systems with desirable performance properties. Journal of Industrial Microbiology & Biotechnology (2000) 24, 389–395. Received 12 August 1999/ Accepted in revised form 23 March 2000     

Cloning and expression of cellulase and xylanase genes in Lactobacillus plantarum

Summary Eleven cellulase genes from Gram-positive bacteria were cloned in a Lactobacillus plantarum silage inoculum. Eight of these genes were expressed as active enzymes from their original promotors and translation signals. Where tested, the enzymes produced by transformed L.plantarum had the same temperature and pH optimum as enzymes produced in the original host, or in transformed Escherichia coli. Using chloramphenicol acetyltransferase as a cell-internal marker enzyme, it could be demonstrated that at least endoglucanase D from Clostridium thermocellum was actively secreted by transformed L. plantarum. In growing L. plantarum cultures, most of the enzymes were irreversibly inactivated when the pH decreased below 4.5. If the transformed strains were to be applied as an inoculum in silage, this pH inactivation might be useful in preventing overdigestion of the crop fibre. Offprint requests to: F. Michiels     

Inoculation of <Emphasis Type="Italic">Pinus halepensis</Emphasis> Mill. with selected ectomycorrhizal fungi improves seedling establishment 2 years after planting in a degraded gypsum soil

Vegetative inoculum of Amanita ovoidea (Bull.) Link and three isolates of Suillus collinitus (Fr.) Kuntze, as well as spore inoculum of Rhizopogon roseolus (Corda) Th. M. Fr. and S. collinitus, were evaluated for the production of Pinus halepensis Mill. in nursery and for the establishment of seedlings in a degraded gypsum soil. In nursery, most of the fungi significantly improved the height of seedlings and modified the accumulation of nutrients in needles. The percentage of ectomycorrhizas (ESR) per seedling ranged from 25 to 78%, depending on the fungi. One and 2 years after planting in the field, the survival of seedlings was significantly improved by inoculation with two isolates of S. collinitus and with spores of the same fungus. Inoculation with A. ovoidea had no significant effect on seedling survival, whilst R. roseolus caused a significant mortality of seedlings. Seedling height was significantly improved by inoculation with all fungi except R. roseolus and isolate CCMA-1 of S. collinitus. One year after planting, mycorrhization of control seedlings was negligible, and percentages of ESR were under 38% for the rest of treatments. In spring of the second year, seedlings in all treatments, including the control, became highly mycorrhizal (60–77% of ESR). Low ectomycorrhizal diversity (five morphotypes described) and seasonal variation on morphotype composition were detected 2 years after plantation. From a perspective of soil restoration management under limiting environmental conditions, nursery inoculation with selected fungi can be a key advantage for tree seedlings to surmount the initial transplant stress, assuring their establishment in the field. Our results emphasise the importance of selecting compatible fungal–host species combinations for nursery inoculation and sources of inoculum adapted to the environmental conditions of the transplantation site.     

Development of a standard bacterial consortium for laboratory efficacy testing of commercial freshwater oil spill bioremediation agents

Six crude oil-degrading bacterial strains isolated from different soil and water environments were combined to create a defined consortium for use in standardized efficacy testing of commercial oil spill bioremediation agents (OSBA). The isolates were cryopreserved in individual aliquots at pre-determined cell densities, stored at −70°C, and thawed for use as standardized inocula as needed. Aliquots were prepared with precision (typically within 10% of the mean) ensuring reproducible inoculation. Five of the six strains displayed no appreciable loss of viability during cryopreservation exceeding 2.5 years, and five isolates demonstrated stable hydrocarbon-degrading phenotypes during inoculum preparation and storage. When resuscitated, the defined consortium reproducibly biodegraded Alberta Sweet Mixed Blend crude oil (typically ± 7% of the mean of triplicate cultures), as determined by quantitative gas chromatography–mass spectrometry of various analyte classes. Reproducible biodegradation was observed within a batch of inoculum in trials spanning 2.5 years, and among three batches of inoculum prepared more than 2 years apart. Biodegradation was comparable after incubation for 28 days at 10°C or 14 days at 22°C, illustrating the temperature tolerance of the bacterial consortium. The results support the use of the synthetic consortium as a reproducible, predictable inoculum to achieve standardized efficacy tests for evaluating commercial OSBA. Received 31 August 1998/ Accepted in revised form 30 November 1998     

The management of populations of vesicular-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem

A field trial was conducted at two sites in the savanna ecosystem of eastern Colombia to compare the effects of inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) ofBrachiaria dictyoneura (a tropical grass), cassava (Manihot esculenta), the tropical forage legume kudzu (Pueraria phaseoloides) andSorghum sp., and two phosphate sources. The second stage of the trial studied the effect of these pre-crop treatments on the subsequent growth, nutrition and VAM status of cowpea (Vigna unguiculata) andStylosanthes capitata in the following season, compared with both crops sown in native savanna. Inoculation significantly increased the levels of VAM and plant yields in the early growth stages of all crops during the first season, particularly with the rock phosphate (RP) source. The most significant increases were observed in the mycorrhiza-dependent cassava and kudzu crops up to 15 weeks after sowing, and were associated with increased foliar uptake of P and Mg. The effectiveness of the introduced inoculum was greater at the field site with a sandier soil. In the second season the levels of VAM in roots of cowpea andS. capitata were all increased significantly in pre-cropped plots compared with a savanna control. The increased presence of VAM was associated with significantly increased yields on plots previously sown to cassava, kudzu andSorghum sp. The data support the idea that increasing the VAMF inoculum potential of these acid-infertile soils by inoculation or pre-crops can greatly increase the rate of establishment of mycorrhiza-dependent host plants.     

Forest farming of shiitake mushrooms: An integrated evaluation of management practices

Two outdoor shiitake (Lentinula edodes) cultivation experiments, established in Missouri USA in 1999 and 2000, produced mushrooms in 2000–2005. We examined shiitake production in response to substrate species, inoculum form, inoculum strain, and inoculation timing, using total mushroom weight per log as the primary response variable with log characteristics as covariates. The significantly greater mushroom weight produced by sugar maple logs compared with white or northern red oak was attributable to the higher proportion of undiscolored wood volume in the maple logs, rather than to bark thickness or log diameter. The “wide temperature range” shiitake strain produced significantly greater yield compared with the “warm” or “cold” weather strains. Both the wide-range and warm-weather strains were stimulated to fruit by significant rain events, while the cold-weather strain was responsive to temperature. Inoculation with sawdust spawn gave significantly greater yield than colonized wooden dowels or pre-packaged “thimble” plug inoculum. The second and third full years following inoculation were the most productive.     

The reactions of susceptible and resistant tomato cultivars to strains of Verticillium albo-atrum

Three strains of Verticillium albo-atrum causing severe wilt of tomato (T), progressive (Hp ) and fluctuating (HF) wilt of hop, were inoculated through the roots of four tomato cultivars at different inoculum concentrations. Symptoms were assessed visually 42 days after inoculation, and quantitatively on the change in total leaf area compared with controls. Distribution of mycelium and tyloses was determined by sections at 2 cm intervals of root, stem and petiole. Cultivars Loran Blood and Moscow showed resistance to disease expression at all levels of inoculum concentration with the T strain. Bonny Best and Potentate were both susceptible to this strain, but whereas in Potentate, disease severity increased from mild to severe with increase in inoculum concentration, Bonny Best was severely diseased at the lowest level of inoculum. All cultivars showed some susceptibility to the HP and HF strains; the ‘resistance’ of Loran Blood and Moscow was no longer apparent and Bonny Best was most severely affected. The relative susceptibilities to the strains were HF Bonney Best > Loran Blood > Potentate > Moscow, HP Bonny Best > Loran Blood, Moscow > Potentate, T Bonny Best > Potentate > Loran Blood, Moscow. In general, vascular colonization was less in the cultivars Loran Blood and Moscow with all three fungal strains at io⁵propagules/ml level of inoculum, but this was not always correlated with an increase in disease severity. With the exception of the host-pathogen combinations Bonny Best/T, Bonny Best/HF, Potentate/T and Moscow/T, increasing the inoculum concentration to 10⁷propagules/ml increased disease severity but had little or no effect of increasing vascular colonization. In Bonny Best/T, Bonny Best/HF and Potentate/T vascular colonization was reduced with the higher level of inoculum. Moscow showed complete resistance to symptom expression and little vascular colonization with the T strain at 10⁵prop./ml. At 10⁷prop./ml resistance was maintained but there was very extensive growth of mycelium in the vessels. Tylosis resulted from an interaction of host, fungal strain and the level of inoculum and was not always correlated with the degree of vascular colonization. Contrary to previous reports the resistant varieties Loran Blood and Moscow developed acute disease symptoms after inoculation with HP and HF and these were associated with a high level of tylosis rather than mycelial growth. Tylosis and disease severity but not mycelial growth increased with higher levels of inoculum. The results suggested that susceptibility to Verticillium wilt was a complex response depending on host cultivar, fungal strain and the initial inoculum concentration. In some cultivar-pathogen combinations susceptibility was directly proportional to the amount of mycelium present in the vessels, while in others a physiological resistance mechanism independent of the degree of colonization appeared to operate. In a third category, increased disease development rather than resistance was associated with high levels of tylosis.     

Rattus norvegicus: not a model for Aeromonas-associated gastroenteritis in man

The lack of a suitable animal model of Aeromonas-associated diarrhoea has hampered investigations into Aeromonas pathogenic mechanisms. Hence, a published report that clindamycin-pretreated rats developed signs and symptoms of enteritis following intragastric inoculation of an Aeromonas strain required further investigation. Although we could demonstrate long-term colonisation (>12 days) and histological damage in this animal model with Pseudomonas aeruginosa isolated from patients with chronic diarrhoea, this was not seen with Aeromonas spp. Six Aeromonas strains, selected for their potential virulence and colonising abilities and including the strain from the original report, were either not recovered from stools or were recovered for no longer than 2 days post inoculation. Intestinal histology remained normal. Destruction of bacteria in vivo appeared to be due to immune mechanisms as inoculum strains were not 'suicidal' or unduly sensitive to low pH or clindamycin. This study was, therefore, unable to validate the clindamycin-treated rat model as a useful one for investigating the enteropathogenicity of Aeromonas species. Possible reasons for the discrepancy between our study and the original report are discussed.     

Effects of some pure and mixedFrankia strains on seedling growth in differentAlnus species

In greenhouse experiments plants of eightAlnus species, from various parts of the world, and from different taxonomic sections, were inoculated with threeFrankia strains in order to show any possible interaction. Mixtures in equal parts of theseFrankia strains were also tried. The growth of inoculated plants was significantly higher than of the controls, with one of the three strains being superior. Mixtures of strains generally provided higher growth than the best individual strain. No interaction betweenFrankia strains andAlnus species was detected in the young plants 60 days after inoculation. Three clones ofAlnus glutinosa were inoculated with the same pure cultures ofFrankia, without producing any interaction. Inoculation time was studied in one clone and one progeny ofAlnus glutinosa. The best results were obtained with the earlier inoculation (at sowing for the progeny and at transfer to soil for thein vitro-propagated clone). The results are discussed in terms of nursery practice and field experiments for selection in breeding programmes.