Plants of saline and sodic soils of the Hungarian steppe and of gypsum rock in the German Harz mountains, thus soils of high ionic strength and electric conductivity, were examined for their colonization by arbuscular mycorrhizal fungi (AMF). Roots of several plants of the saline and sodic soils such as Artemisia maritima, Aster tripolium or Plantago maritima are strongly colonized and show typical AMF structures (arbuscules, vesicles) whereas others like the members of the Chenopodiaceae, Salicornia europaea, Suaeda maritima or Camphorosma annua, are not. The vegetation of the gypsum rock is totally different, but several plants are also strongly colonized there. The number of spores in samples from the saline and sodic soils examined is rather variable, but high on average, although with an apparent low species diversity. Spore numbers in the soil adjacent to the roots of plants often, but not always, correlate with the degree of AMF colonization of the plants. As in German salt marshes [Hildebrandt et al. (2001)], the dominant AMF in the Hungarian saline and sodic soils is Glomus geosporum. All these isolates provided nearly identical restriction fragment length polymorphism (RFLP) patterns of the internal transcribed spacer (ITS) region of spore DNA amplified by polymerase chain reaction (PCR). Cloning and sequencing of several PCR products of the ITS regions indicated that ecotypes of the G. geosporum/ Glomus caledonium clade might exist at the different habitats. A phylogenetic dendrogram constructed from the ITS or 5.8S rDNA sequences was nearly identical to the one published for 18S rDNA data (Schwarzott et al. 2001). It is tempting to speculate that specific ecotypes may be particularly adapted to the peculiar saline or sodic conditions in such soils. They could have an enormous potential in conferring salt resistance to plants.

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We isolated two bacterial strains from an experimentally lead (Pb)-polluted soil in Hungary, 10 years after soil contamination. These strains represented the two most abundant cultivable bacterial groups in such soil, and we tested their influence on Trifolium pratense L. growth and on the functioning of native mycorrhizal fungi under Pb toxicity in a second Pb-spiked soil. Our results showed that bacterial strain A enhanced plant growth, nitrogen and phosphorus accumulations, nodule formation, and mycorrhizal infection, demonstrating its plant-growth-promoting activity. In addition, strain A decreased the amount of Pb absorbed by plants, when expressed on a root weight basis, because of increased root biomass due to the production of indoleacetic acid. The positive effect of strain A was not only evident after a single inoculation but also in dual inoculation with arbuscular mycorrhizal fungi. Strain A also exhibited higher tolerance than strain B when cultivated under increasing Pb levels in the spiked soil. Molecular identification unambiguously placed strain A within the genus Brevibacillus. We showed that it is important to select the most tolerant and efficient bacterial strain for co-inoculation with arbuscular mycorrhizal fungi to promote effective symbiosis and thus stimulate plant growth under adverse environmental conditions, such as heavy-metal contamination.

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Alfalfa (Medicago sativa L.) plant growth decreases when cultivated under salinity or irrigated with salty water. Inoculation with plant growth-promoting bacteria (PGPB) is a method for mitigating the harmful effects of salinity on plants growth. To investigate salt-tolerant PGPB with salt-tolerant and salt-sensitive alfalfa cultivar interactions under salinity, some physiological and agronomical aspects were investigated. The inoculated plants of alfalfa cultivars with Hartmannibacter. diazotrophicus and Pseudomonas sp. bacteria were compared with non-inoculated plants. Plants were grown in growth room and irrigated with tap water until 6-7 weeks, and then, salinity stress imposed by irrigating with tap water (control), 10 dS m −1 and 20 dS m −1 NaCl. Salinity reduced relative water content (RWC), membrane stability index (MSI), K + , photosynthesis rate (Pn) and stomatal conductance (gs), leaf number, height, and dry weight, and increased sodium in all cultivars. Inoculation of cultivars with both PGPB mitigated the negative effects of salinity on plants growth by increasing the root length and weight, nodule number, chlorophyll pigments, RWC, MSI, Pn, and gs. Chlorophyll pigments, plant height and leaf number, Na + , K + /Na + , and nodule number improved more pronounced through inoculating with Pseudomonas sp., whereas K + , carotenoids, and RWC improved more pronounced through H. diazotrophicus under salinity. The results showed inoculation with two bacteria improved growth performance in salt-tolerant and salt-sensitive cultivars under 10 dS m −1 , but at high salinity (20 dS m −1), inoculation was successful only in salt-tolerant alfalfa cultivars.