Anti-transpiration and anti-growth activities of xylem sap were studied for maize, sunflower, cotton and castor bean, which were subjected to several stress treatments: soil drying, flooding and salinity. All samples of xylem sap showed an increased concentration of proteins when plants were either soil-dried, salt-treated or flooded. The protein transportation flux in xylem sap, i.e. the product of protein concentration and volume flux, was also increased as a result. Electrophoresis using SDS–PAGE analysis showed that xylem proteins were of variable size. When samples of xylem sap were used to feed detached leaves or shoots in a bioassay system for their anti-transpiration and anti-growth activities, such xylem proteins in their original concentrations apparently showed neither direct inhibition nor enhanced effects of ABA. All samples of xylem sap from plants subjected to different stresses showed anti-transpiration and anti-growth activities that could be fully accounted for by their ABA concentration. In cases where such activities were more than could be explained by the ABA concentrations, filtration with a 0·20 μm microfilter removed the discrepancies.

Improving the drought resistance of high yielding rice (Oryza sativa L.) varieties for upland areas is a goal of rice breeders since upland rice relies exclusively on rainfall for water and is generally low yielding. Identifying quantitative trait loci (QTLs) which confer drought resistance promises to speed this goal. We have previously described the use of 82 restriction fragment length polymorphism (RFLP) markers in the genetic mapping of root growth characteristics that are potentially involved in drought resistance in a population of 178 F2 plants derived from a cross of two drought resistant upland varieties, Azucena and Bala. Here we report the characterization and QTL mapping of three other mechanisms of drought resistance, leaf rolling, stomatal behaviour and early flowering, in this population. When the youngest fully expanded leaf was excised from 12 rice varieties, ‘IR20’ and ‘Bala’ were identified as slow at rolling. Although ‘Azucena’ rolled its leaves much faster than ‘Bala’ upon excision, stomatal resistance rose more rapidly in ‘Bala’, resulting in a lower rate of water loss. By assessing leaf rolling and stomatal resistance in the F2 population, it was possible to identify QTLs for these traits. A QTL for slow leaf rolling from ‘Bala’ was found on chromosome 1. Two QTLs associated with resting stomatal conductance were found on chromosomes 3 and 12. QTLs for the rate of stomatal closure were found on chromosomes 3 and 7. In addition, it was possible to map QTLs associated with the days to heading which were found on chromosomes 3, 8 and 10. These results identify markers of potential value to breeders and are discussed in the context of previously reported data for heading date QTLs in rice and for stomatal conductance QTLs in maize.

The components of leghaemoglobin (Lb) from twelve different Pisum sativum L. cvs and three near-isogenic foliar mutants were investigated by anion-exchange high-performance liquid chromatography (HPLC). Five different Lb component profiles could be found. The number of components varied from four to six dependent on cultivar used. An Lb pattern composed of four Lb components could be detected in thirteen P. sativum cultivars and lines. Ten of them showed an identical profile. In nodules of each cultivar, the two known major components, LbI and LbV, but also LbIV, could be detected. Additionally, cultivar-specific Lb components could be identified, each representing up to 10% of total Lb. One of these components, LbIII, has been described previously, but three new Lb components (LbII, LbVI, and LbVII) were found. The presence of all Lb components detected by HPLC was confirmed by analytical isoelectric focusing. Further, it was shown that age-dependent changes in the relative concentrations of LbI and LbV are common in P. sativum and that these variations are independent of breeding lines and cultivars.

A strain of non-pathogenic Fusarium oxysporum Schlecht. emend. Snyd. & Hans. has been selected for its capacity to reduce the incidence of Fusarium wilt of tomato. Among the possible modes of action of this strain, competition with the pathogen for the colonization of the root surface and tissues has been proposed. In order to study the pattern of root colonization, young Lycopersicon esculentum Miller (tomato) plants grown in a nutrient solution were inoculated by a suspension of F. oxysporum microconidia and processed at time-intervals for microscopic observations. The fungal strain was transformed with the Gus reporter gene to facilitate the observations. Within 24 h of inoculation the root surface was colonized by a dense network of hyphae, with the exception of the apex, which was colonized only after 48 h. A few hyphae were observed penetrating into the epidermis, leading to the internal colonization of the root cortex. This colonization was always discontinuous, since defence reactions of the plant limited the extension of the fungus. The barrier formed by thickenings and coilings of the cell walls and hypertrophied cells was most frequently observed in the external cortex and, sometimes, deeper in the internal cortex, close to the vessels which were never colonized. Typical defence reactions such as wall appositions, intercellular plugging and intracellular osmiophilic deposits, were frequently observed. This is the first report, based on microscopic observations, of the capacity of a non-pathogenic strain of F. oxysporum to colonize roots of tomato.

High levels of soil aluminium place serious constraints on wheat production on acidic soils, especially in the tropical areas of Africa and South America. Conventional plant breeding has improved the tolerance of the wheat crop, but available genetic variation is limited. The wild relatives of wheat provide a valuable gene pool for the introduction of further genetic variation. One wild species, Aegilops uniaristata Vis. (2n=2x=14,NN), is being utilized as a new source of tolerance. Of the addition lines of individual N genome chromosomes of A. uniaristata to wheat (Triticum aestivum L.) which have been established and characterized, chromosome 3N has been shown to confer tolerance to wheat. The three substitution lines in which 3N replaces the homoeologous wheat chromosomes, 3A, 3B or 3D, have also been produced. Growing plants to maturity in a low pH/high Al hydroponics system confirmed that chromosome 3N conferred tolerance to the substitution lines as well as to the addition line. By manipulating the genetic control of homoeologous chromosome pairing, chromosome 3N is being recombined with its wheat homoeologues in order to introduce a smaller alien segment which carries the gene(s) for tolerance but not the agronomically unacceptable brittle rachis gene also carried on chromosome 3N.

Actinomycetes isolated from carrot rhizosphere were screened for their in vitro and in vivo antagonism to Pythium coloratum Vaartaja, a causal agent of cavity-spot disease of carrots (Daucus carota L.). Forty-five streptomycete and non-streptomycete actinomycete isolates were screened for in vitro antagonism in a carrot bioassay. Of these, seven which reduced or prevented lesion formation were identified using cultural, morphological, physiological, biochemical and cell wall characteristics as Streptomyces janthinus, S. cinerochromogenes, Streptoverticillium netropsis, Actinomadura rubra, Actinoplanes philippinensis, Micromonospora carbonaceae, and Streptosporangium albidum. All seven isolates tested produced non-volatile antifungal metabolites, but failed to produce inhibitory volatile compounds. Actinoplanes philippinensis and M. carbonacea grew epiphytically on the hyphae and oospores of P. coloratum. The external surface of the oospores of the pathogen was heavily colonized by both hyperparasites, their hyphae were found to coil tightly around the oospore wall, and frequently caused cytoplasmic collapse of oospores. Sporangia of A. philippinensis were often seen to emerge from the colonized hyphae and oospores of P. coloratum. None of the other actinomycete isolates showed hyperparasitism.

All seven isolates significantly reduced the incidence of cavity spot in soil artificially infested with the pathogen in the glasshouse. Streptomyces janthinus and Strepto. albidum were the most effective in reducing the disease in inoculated plants. In addition, all the actinomycetes species except Ac. rubra and M. carbonacea, in the presence or absence of the pathogen, significantly (P<0·05) increased mean fresh root weight compared to the treatment which included P. coloratum only. This study shows that these actinomycetes have considerable potential for future use as biocontrol agents of cavity spot under natural field conditions. This is the first report of cavity-spot disease of carrots being controlled by microbial antagonists, and is the first report of non-streptomycete actinomycetes to control a Pythium disease.

We examined the importance of seed size in the early establishment of seedlings of four cotyledonous species restricted to nutrient-impoverished soils in south-western Australia. Experimentally removing cotyledons from seedlings increased mortality and reduced root-penetration, growth rate and final weight of plants after 12 wk, in proportion to seed size. The impact of removal of the cotyledons was least in the smallest-seeded, Eucalyptus loxophleba Benth., grown in the more fertile of two soils, and greatest in the largest-seeded, Hakea psilorrhyncha R. M. Barker, whose growth was otherwise unaffected by soil type. In the smallest-seeded species, cotyledon content of most mineral nutrients increased over time, especially in the more fertile soil, while chlorophyll content showed some decrease by the end of the experiment. In the other species, most nutrients (especially N, P, K and Cu in the less fertile soil) were translocated from the cotyledons to the growing plant, and chlorophyll content declined markedly. The translocated N, P, K, Mg and Cu in these species made up a substantial part of the total plant content by 12 wk after germination, while total Ca and Fe tended to increase in the cotyledons via substantial soil uptake. The results indicate, contrary to reports for some other species, that the cotyledons have an important nutritional function in the early establishment of seedlings in these species. The results also show that, in the larger-seeded species, young seedlings rely to a greater extent on nutrient support from the cotyledons than from the soil. We propose that large seeds might be an adaptation for enhancing establishment in nutrient-poor soils.

The growth of the grass Brachypodium pinnatum (L.) Beauv. in Dutch nutrient-poor chalk grasslands increases with enhanced nitrogen supply, whereas other grass species also require an enhanced phosphorus supply for a similar response (e.g. Dactylis glomerata L.), or are competitively suppressed at any increase in nutrient supply (e.g. Briza media L.). We investigated whether this interspecific variation in response to N and P supply is caused by differences in P productivity (PP), i.e. the instantaneous rate of biomass production per unit of P present in the plant. We hypothesized that PP is highest in Brachypodium pinnatum, in contrast to N productivity which is known to be the highest in Dactylis glomerata. Phosphorus productivity and its components were studied using a growth analysis with four exponential P addition rates of 0·03, 0·06, 0·09 and 0·11/0·15 mg P mg−1 P d−1.

Although Brachypodium pinnatum allocated more P to its leaf blades, it had a lower P productivity at high N and low P supply than did Dactylis glomerata. This was associated with a higher productivity per unit leaf P in Dactylis glomerata. Across all species and treatments, leaf PP showed a distinct negative correlation with P concentration per leaf area, regardless whether the variation in area-based leaf P concentration was caused by variation in leaf thickness, leaf tissue mass density or mass-based P concentration. A possible explanation for this would be a positive correlation between leaf chlorophyll concentration and P concentration, leading at high concentrations to shading within the leaf and to a low photosynthetic rate per unit leaf P. We conclude that a high PP is determined by the ability of a plant to distribute its P over a large leaf area, rather than by greater allocation of P to the leaves. Interspecific relationships for P productivity are similar to those known for N productivity.

IAA production by the ectomycorrhizal fungus Paxillus involutus grown in pure culture was investigated by testing IAA accumulation or IAA-synthesizing activity. All the Paxillus involutus strains studied released indole compounds either when incubated with 0·5 mm tryptophan or in its absence. HPLC analyses of indole compounds all yielded two main peaks identified by reference to controls as being IAA and indole-3-carboxylic acid and a small peak of indole-3-aldehyde. Mass spectrometry unequivocally confirmed IAA production in the culture filtrates and in the incubation solution used to study in vitro IAA-synthesizing activity. The IAA-synthesizing activity was found to vary widely, from 7·6 to 137·4 nmol IAA h−1 g−1 f. wt, between strains. The mycorrhizal activity of these strains with seedlings of Pinus sylvestris cultured under aseptic conditions was tested. Fungal strains that were characterized in pure culture conditions by high IAA-synthesizing activity induced more fine roots and significantly higher numbers of mycorrhizas than strains which showed a low activity of IAA synthesizing enzymes. The increased ectomycorrhiza formation was generally accompanied by an increased growth of seedlings.

Drought strongly affects cereal yield in several regions of the world. Plant growth and plant water status in response to soil water deficit play an important role in tolerance to drought and in yield stability. In order to investigate the relationship between plant growth and water relations, 187 barley (Hordeum vulgare L.) recombinant inbred lines from a cross between two Mediterranean varieties, Tadmor and Er/Apm, were studied in a growth chamber for RWC, number of leaves on the main tiller (NL), number of tillers (NT) and total shoot fresh and dry biomass (TSFM and TSDM). Measurements were made at the beginning of tillering on well watered plants and at a soil moisture content of 14% of field capacity. A negative phenotypic correlation between RWC and growth parameters was obtained in both treatments. Under water stress, a negative genetic correlation was also found between the same characters. QTLs involved in RWC, NL and TSFM variation were positioned on a RFLP-RAPD genetic map. Different DNA regions involved in constitutive and water stress responses were detected. In the stress treatment, one region on chromosome 1 was involved in RWC and NL variation giving a genetic basis to the phenotypic correlations found. Separated map positions were also found for RWC and NL. Epistatic interactions between several QTLs and between QTLs and other markers were detected only in the water stress treatment, suggesting that some chromosomal regions might be involved in the regulation of the expression of the traits under water stress. This work suggested that even if some parameters are strongly correlated, finding QTLs for only one trait is not sufficient to detect all the candidate regions which might be involved in the control of the correlated traits. The results of localization and co-localization of QTLs are physiologically interpreted.

Nine different clones of six species of Salix (Salix cordata Muhlenb. non Michaux, S. fragilis L., S. caprea L., S. cinerea L., S. burjatica Nazarov. and S. viminalis L.) and one hybrid (S.×calodendron Wimm.) were exposed to heavy metals in solution culture in an attempt to increase innate metal resistance. Resistance was estimated using comparative root measurements, and metal uptake was also studied. The first experiment entailed pretreatments with background nutrient solution, or 0·25 and 0·50 mg Cu l−1 amendments, and re-exposure to each of the same concentrations. In a second experiment clones were exposed to sub-toxic concentrations of single metals (0·15 mg Cu l−1, 0·15 mg Cd l−1 or 2·5 mg Zn l−1) and dual-combination treatments (0·075 mg Cu l−1+0·075 mg Cd l−1, 0·075 mg Cu l−1+1·25 mg Zn l−1 or 0·075 mg Cd l−1+1·25 mg Zn l−1)1 with concentrations gradually raised 10-fold over 128 d. Plants tested in the first experiment, following pre-exposure to Cu, were no more resistant to subsequent exposure to this metal. In the second experiment, gradual cumulative doses resulted in reduced phytotoxicity and increased resistance, most notably to Cd. There appeared to be an inverse relationship between metal uptake and resistance. Copper uptake was restricted to the roots, whereas Cd and Zn were more evenly distributed throughout the plant. Exposure to dual combinations of metals resulted in several interaction effects on uptake: increased root-bound Cu in all combinations, and the increase in uptake of both Cd and Zn into the root tissues when supplied with Cu. The implications of these results for the use of willows in phytoremediation programmes are discussed.

Birch cuttings (Betula pendula Roth) were grown in a sand-culture system with two concentrations (0·05, HF and 0·005%, LF) of fertilizer containing macronutrients and micronutrients, and were exposed to 90/40 nl l−1 O3 (day/night) and <3 nl l−1 O3 (control) for one growing season in the field fumigation chambers at Birmensdorf (Switzerland). Leaves of different ages were analysed for gas exchange, contents of chlorophyll, protein, and for metabolites as well as enzyme activities of carbohydrate metabolism.

Ozone reduced net photosynthesis and chlorophyll contents in mature leaves of both fertilization treatments, whereas that of protein was only reduced in high-fertilized plants (HF). However, net photosynthesis, chlorophyll, and protein increased in young leaves of low-fertilized plants (LF). The effects of ozone on enzyme activities of carbohydrate metabolism were most pronounced in leaves of LF plants. Specific activities of the sucrose-cleaving enzymes, sucrose synthase and alkaline invertase, were induced, whereas acid invertase was unchanged. Extractable activity of sucrose phosphate synthase, which is a key enzyme of sucrose synthesis, was reduced. Levels of fructose 2,6-bisphosphate, an inhibitor of sucrose synthesis, were increased in leaves of O3/LF plants, but reduced in O3/HF plants. In addition, activities of enzymes involved in starch metabolism, ADP-glucose pyrophosphorylase and starch phosphorylase, were lowered in ozone-treated samples and the ratio of ATP[ratio ]ADP was increased.

It is concluded that chronic ozone exposure leads to an inhibition of sucrose synthesis and favours sucrose degradation. This effect is modulated by the nutrient status of the plants, indicating higher O3 tolerance in HF plants. Furthermore, as the metabolic responses in the ozone-treated samples resemble very closely those observed under end-product inhibition of photosynthesis, we assume that the O3 effect is mainly due to reduced photosynthate export.

A common feature of many pollutant exposure studies is that data from these experiments often consist of either plant biomass or yield, and the response to the pollutant is usually based on a simple comparison of means determined at the end of each growing season. This type of data is now being used to quantify critical levels for different types of vegetation. Such an approach is, however, inappropriate for the relatively short-term exposure studies with trees since, due to their longevity, it is not possible to determine a final yield. Instead these studies should be regarded as a type of intervention experiment in which only a small part of the life cycle of the tree is investigated. Moreover, critical levels as they are now defined focus on the cumulative exposure to ozone concentrations over time. Hence, any analysis of the effects of ozone on the growth of trees should similarly focus on the behaviour of growth functions over time and not on a comparison of biomass at the end of a growing season or experiment.

Here we report on the statistical analysis of a longitudinal study, where the term ‘longitudinal’ refers to the analysis of repeated measurements over time, and which was used to investigate relative differences in the growth of Sitka spruce and Norway spruce seedlings during three summers' exposure to ozone over three (Norway) or four (Sitka) growing seasons. Measurements of total seedling height and stem diameter were made at frequent intervals over the period of the experiment and the above-ground growth of individual trees (as log d2h) analysed for each growing season using a statistical model of the form: m(t)=a+b(t−t0). No statistically significant differences in the growth of Norway spruce were observed after three summers of ozone exposure. The growth of Sitka spruce was, however, reduced by ozone during the third growing season and in the following year, even in the absence of the pollutant.

For the Sitka spruce, the fitted model was used to calculate the time at which a 10% reduction in growth had occurred in the ozone-exposed trees. In combination with ozone AOT40 indices for the relevant growing seasons, this was then used to determine a critical level of 21·3 ppm-h for this species. Since the growth of the Norway spruce was unaffected by exposure to ozone it was not possible to calculate a critical level other than to surmise that it is in excess of 30 ppm-h.

Variation for K+ and Na+ accumulation at low salinities in hydroponic (water) culture were observed in shoots of different wheat species. Greater discrimination (in favour of K+ and against Na+ accumulation) was shown by hexaploid bread wheat (Triticum aestivum L.) than by tetraploid durum wheat (T. turgidum L.). Since Aegilops tauschii Cosson (A. squarrosa L.), the source of the D genome in bread wheat, also exhibited high discrimination between K+ and Na+, it was concluded that the character resided in the D genome. Studies of aneuploid bread wheat lines and disomic substitution lines of D genome chromosomes for their A and B genome homoeologues in durum wheat cv. Langdon revealed that the trait was controlled by the long arm of chromosome 4D. Since the aneuploid and disomic substitution lines showed better relative salt tolerance than durum wheat, but had lower yield potentials, we recombined chromosome 4D with chromosome 4B in a tetraploid wheat background using a homoeologous pairing mutant. This produced families of 4D/4B recombinant lines, some of which exhibited the enhanced K+/Na+ discrimination trait. RFLP analysis confirmed that the trait was controlled by a single gene (Kna1) which was completely linked to five markers on the distal third of the long arm of 4D. A second cycle of homoeologous recombination was employed to remove the distal 4D genetic material from the recombined Kna1 4B/4D chromosome and to map Kna1 in greater detail. By this strategy, Kna1 was mapped within a short 2 cM region. Genetic analysis of K+[ratio ]Na+ ratios showed very high LOD scores in this region for plants grown in solution culture, but lower values for plants grown in the field.

In general, recombinant lines which exhibited the enhanced K+/Na+ trait were slightly more tolerant of salinity in the field and in sand culture than recombinants lacking the trait. There was, however, considerable variation between individual lines. Ion discrimination and relative tolerance were also higher in a Kna1 recombinant (line no. R3) than in a kna1 recombinant (line no. R165) in sodic conditions. In these two lines the enhanced K+/Na+ discrimination trait did not alter responses to low potassium or calcium supply.

Longleaf pine (Pinus palustris Mill.) seedlings were exposed to two concentrations of atmospheric CO2 (365 or 720 μmol mol−1) and two levels of N (0·02 or 0·20 mg N g−1 soil yr−1) within open-top chambers for 20 months. Seedlings were adequately watered for 19 wk to ensure seedling establishment, after which two water-stress treatments (target values −0·5 or −1·5 MPa xylem pressure potential) were implemented. Fine-root samples were collected in July and November 1993, and in March and November 1994. Ectomycorrhizal and non-mycorrhizal short roots per unit length of fine root were quantified. The percentage of ectomycorrhizal short roots and numbers of ectomycorrhizas per unit root length were higher for seedlings grown with elevated CO2, low N and adequate water. Interactions among main treatment variables demonstrated higher percentages of ectomycorrhizal short roots, fine root length per seedling, and total numbers of ectomycorrhizas per seedling for plants grown with high CO2 (compared with ambient) or adequate water (compared with water stress) only under high N conditions. Increased fine-root length and ectomycorrhizal colonization under elevated CO2 resulted in higher (almost double) numbers of ectomycorrhizas per seedling at each sampling.

Seedlings of Pseudotsuga menziesii (Mirb.) Franco, Pinus ponderosa Dougl. ex Laws, Arbutus menziesii Pursh., and cuttings of Arctostaphylos uva-ursi (L.) Spreng were grown in monoculture and in conifer-hardwood dual-culture combinations in the glasshouse and inoculated with spore slurries of six Rhizopogon species. The primary objectives were to assess and compare the pattern of host specificity between symbionts and to study the influence of co-cultured plants on ectomycorrhiza development. The Rhizopogon spp. ranged from genus-specific to multiple-host compatible. In monoculture, four Rhizopogon sp. (R. ellenae Smith, R. occidentalis Zeller & Dodge, R. smithii Hosford and R. subcaerulescens Smith) formed ectomycorrhizas with Pinus ponderosa, and two Rhizopogon sp. (R. parksii Smith and R. vinicolor Smith) formed ectomycorrhizas with Pseudotsuga menziesii. None of the fungi tested developed ectomycorrhizas on Arbutus menziesii or Arctostaphylos uva-ursi in monoculture. In dual culture, three of the four Rhizopogon species (R. ellenae, R. occidentalis and R. subcaerulescens) that formed ectomycorrhizas on Pinus ponderosa, formed some ectomycorrhizas on Arbutus menziesii and Arctostaphylos uva-ursi. Rhizopogon parksii and R. vinicolor only formed ectomycorrhizas on Pseudotsuga menziesii.

Two families of Helianthus lines, T− (low desiccation rate) and T+ (low desiccation rate), with contrasting osmotic adjustment (OA), obtained from a divergent selection programme, were compared for several morphological traits, ecophysiological parameters and molecular markers. The physiological analysis in a glasshouse experiment showed that the two families were identical in irrigated conditions except for a single trait, relative water loss (RWL: water loss rate of excised leaves). RWL could be used for these genotypes as a physiological marker of OA. A molecular analysis of the two contrasting lines, using differential screening of cDNA libraries, led to the isolation of three specific cDNAs, one of which, DRS26, showed high sequence homology with a mammalian amino-acid transporter. Subsequent RFLP and STS studies, using DRS26 and RAPD bulked analysis, enabled the identification of putative molecular markers of RWL and OA in T−[ratio ]T+ sunflower.

Interspecific C transfer was studied in laboratory microcosms containing pairs of 6-month-old Betula papyrifera Marsh. and Pseudotsuga menziesii (Mirb.) Franco seedlings growing in individual, root-restrictive (28 μm pore size) pouches filled with field soil. Interspecific transfer was examined by reciprocal labelling of seedlings with 13CO2(gas) and 14CO2(gas). At the time of labelling, the root zones of ectomycorrhizal (EM) B. papyrifera and P. menziesii were interconnected by an extensive network of EM mycelium. Carbon transferred through EM connections was distinguished from that through soil pathways by comparing microcosms where interconnecting hyphae were left intact vs. those where they were severed immediately before labelling.

Transfer was bidirectional, and represented 5% of total isotope uptake by both B. papyrifera and P. menziesii together. P. menziesii received on average 50% more 14C and 66% more 13C from paper birch than vice versa, however, differences between species were not statistically significant. Neither net nor bidirectional transfer differed between severing treatments, leaving in question the relative importance of EM hyphae versus soil transfer pathways. The tendency for P. menziesii to receive more isotope than B. papyrifera corresponded with a 10-fold greater net photosynthetic rate per seedling and two-fold greater foliar N concentration of B. papyrifera than P. menziesii.

Genetic diversity, population genetic structure and gene flow in Calluna vulgaris (L.) Hull were assessed by means of seven allozyme loci scored in 18 populations from the South-Western area of the species' range. Genetic diversity was lower (HT=0·20) than reported for long-lived widespread species but was characterized by a high number of alleles per locus (5·60 at the species level) of which more than 70% were rare. More than 95% of genetic variation was found at the intrapopulation level (GST=0·047). High levels of past gene flow were inferred, based on the allozyme data (Nm=5·2 from GST, Nm=10·2 from the ‘private allele’ method). Calluna vulgaris exhibited several geographic patterns of genetic variation. Both cluster analysis, constructed with various genetic distances and principal components analysis showed that Spanish and Pyrenean populations were clearly different from those collected in the Massif Central and Belgium. Also, a trend for decreasing genetic diversity towards Northern populations was detected. These patterns might be related to the post-glacial history of Calluna. In addition, it is shown that isolation by distance has played a role in the geographic shaping of genetic variation in this species.

The identity of individual ectomycorrhizas, root colonization patterns and early growth responses of interconnected Scots pine (Pinus sylvestris L.) seedlings were investigated following interactions between local genets of Suillus bovinus (L. ex Fr.) O. Kuntze (SBK4b and SBK5b) and S. variegatus (Swartz ex Fr.) O. Kuntze (SVK3b) and different host–genotype combinations. Three equidistant 39-d-old seedlings, in pots that contained sterile N-limited nursery soil, were each inoculated with one of the three genets in the multiple inoculation treatment (MIT). Single inoculation treatments (SITs), involving inoculation of only one seedling in the triad with one of the three genets, and a similarly configured uninoculated treatment (UIT), were also prepared for comparative analysis. All seedling roots in the inoculated treatments, except for one SIT/SBK4b combination, hosted large numbers (>150) of Suillus-type ectomycorrhizas after 23–25 wk growth without additional fertilization. Esterase (EST) isozyme analysis of individual ectomycorrhizas from all SIT and MIT combinations enabled efficient interspecific and intraspecific typing of fungal (genet) colonization (89 and 72%, respectively) and identification of host genotype variation (Z locus polymorphism) at a lower rate (51%). Species, but not S. bovinus genet, typing within randomly sampled individual ectomycorrhizas from selected SITs was successful (50–70%) following PCR/RFLP analysis of diagnostic sequences of fungal rRNA genes. In the SITs, only the inoculated fungal genet was detected in ectomycorrhizas on all three seedlings. Roots were predominantly colonized by SBK4b in one, and SBK5b in three, of the MIT combinations, although ectomycorrhizas of the former genet were detected at low frequencies on nearly all seedlings. In the remaining MIT combination, both SBK4b and SVK3b were found to co-dominate as ectomycorrhizas on the seedling roots. Small numbers of the latter genet were detected in ectomycorrhizas of two SBK5b-dominated MIT combinations. However, no significant trends in host-mycorrhiza interactions were detected using a log–linear analysis. Compared with the UIT, significant positive mycorrhizal plant growth responses, particularly increased needle length, were recorded in all the heavily colonized seedlings in most SIT and all MIT combinations. Intermediate seedling growth was restricted to the one SIT/SBK4b combination where seedlings supported limited numbers of ectomycorrhizas. The general host-fungal colonization patterns observed provide further below-ground evidence supporting genet interactions previously detected through sporocarp population analyses in young Scots pine reforestation sites.