<Emphasis Type="Italic">In vitro</Emphasis> propagation of <Emphasis Type="Italic">Zingiber petiolatum</Emphasis> (Holttum)

Summary We describe an in vitro propagation protocol for Zingiber petiolatum (Holttum), I. Theilade, a rare species from the southern part of Thailand. Fruits were surface-sterilized and seeds germinated on Murashige and Skoog medium (MS) medium supplemented with 3% sucrose. Three-month-old seedlings were used as initial plant material for in vitro propagation. Terminal buds of the plants were inoculated on MS medium containing 6-benzylaminopurine (BA; 2.2–35.5 μM) alone or in combination with 1-naphthaleneacetic acid (0.5 μM). Eight weeks after inoculation, the cultures were transferred to MS medium without plant growth regulators for 4wk. The cultures transferred from MS medium with 17.8 μM BA revealed the highest shoot induction rate of 6.1±0.7 shoots per explant. Rooting was spontaneously achieved in MS medium without plant growth regulators. Rooted plants were successfully transplanted to soil.     

The potential of <Emphasis Type="Italic">Rhizobium</Emphasis> strains for biological control of <Emphasis Type="Italic">Orobanche crenata</Emphasis>

Orobanche crenata Forsk is a chlorophyll lacking holoparasite that subsists on the roots of plants and causes significant damage to the culture of leguminous plants and, in particular, to peas (Pisum sativum L.). Here, we investigated the potential of Rhizobium strains for biological control of Orobanche crenata using a commercial pea cultivar (Douce de province) and different Rhizobium strains. Firstly, benefit of bacterial inoculation on plant growth and efficiency in N-incorporation were demonstrated with four isolates, P.SOM, P.1001, P.Mat.95 and P.1236. After five Rhizobium strains (three efficient: P.SOM, P.1236, P.Mat.95 and two not efficient: P.OM1.92, P.MleTem.92) were investigated for their ability to control Orobanche crenata using pot and Petri dish experiments. Inoculation of peas with two (P.SOM and P.1236) of the five strains induced a significant decrease in O. crenata seed germination and in the number of tubercles on pea roots. Furthermore, other symptoms, including the non-penetration of the germinated seeds into pea roots followed by radicle browning and death of the parasites, were observed in the presence of these inoculated pea plants. The hypothesis that roots secrete toxic compounds related to Rhizobium inoculation is discussed.     

Ectopic expression of <Emphasis Type="Italic">Dahlia merckii</Emphasis> defensin <Emphasis Type="Italic">DmAMP</Emphasis>1 improves papaya resistance to <Emphasis Type="Italic">Phytophthora palmivora</Emphasis> by reducing pathogen vigor

Phytophthora spp., some of the more important casual agents of plant diseases, are responsible for heavy economic losses worldwide. Plant defensins have been introduced as transgenes into a range of species to increase host resistance to pathogens to which they were originally susceptible. However, the effectiveness and mechanism of interaction of the defensins with Phytophthora spp. have not been clearly characterized in planta. In this study, we expressed the Dahlia merckii defensin, DmAMP1, in papaya (Carica papaya L.), a plant highly susceptible to a root, stem, and fruit rot disease caused by Phytophthora palmivora. Extracts of total leaf proteins from transformed plants inhibited growth of Phytophthora in vitro and discs cut from the leaves of transformed plants inhibited growth of Phytophthora in a bioassay. Results from our greenhouse inoculation experiments demonstrate that expressing the DmAMP1 gene in papaya plants increased resistance against P. palmivora and that this increased resistance was associated with reduced hyphae growth of P. palmivora at the infection sites. The inhibitory effects of DmAMP1 expression in papaya suggest this approach has good potential to impart transgenic resistance against Phytophthora in papaya.     

Bacterial Cr(VI) Reduction Concurrently Improves Sunflower (<Emphasis Type="Italic">Helianthus Annuus</Emphasis> L.) Growth

Four Cr(VI)-reducing bacterial strains (Ochrobactrum intermedium, CrT-2, CrT-3 and CrT-4) previously isolated from chromium-contaminated sites were inoculated on to seeds of sunflower (Helianthus annuus var SF-187), which were germinated and grown along with non-inoculated controls with chromate salts (300 μg CrCl₃ or K₂CrO₄ ml⁻¹). Severe reduction (20%) in seed germination was observed in Cr(VI) stress. Plant height decreased (36%) with Cr(VI) when compared with chromium-free control, while O. intermedium inoculation resulted a 20% increment in this parameter as compared to non-inoculated chromium-free control. CrT-3 inoculation resulted a 69% increment in auxin content as compared to non-inoculated control. O. intermedium caused 30% decrease in chromium uptake in sunflower plant roots under Cr(VI) stress as compared to chromium-free control plants.     

Electrofusion of protoplasts from <Emphasis Type="Italic">Solanum tuberosum</Emphasis>, <Emphasis Type="Italic">S. bulbocastanum</Emphasis> and <Emphasis Type="Italic">S. pinnatisectum</Emphasis>

This paper discusses a number of experiments performed, involving the fusion by an electric field of mesophyll protoplasts from Solanum tuberosum cv. Bintje, S. tuberosum dihaploid clones 243, 299 and the wild tuberous disease-resistant species S. bulbocastanum and S. pinnatisectum. Three fusion experiments (S. bulbocastanum + S. tuberosum dihaploid 243, S. pinnatisectum + S. tuberosum cv. Bintje and S. pinnatisectum + S. tuberosum dihaploid 299) yielded 542 calli, the 52 ones of which produced shoots. Obtained regenerants were estimated by the flow-cytometry (FC) and RAPD analysis to determine hybrid plants.The utilisation of the FC as a useful method for detecting somatic hybrids is also discussed in this paper. The combination S. bulbocastanum + S. tuberosum dihaploid 243 led to the creation of eight somatic hybrids, the combination S. pinnatisectum + S. tuberosum cv. Bintje yielded four somatic hybrids and the combination S. pinnatisectum + S. tuberosum dihaploid 299 resulted in no hybrid regenerants. Morphology in vitro, growth vigour and production of tuber-like structures were evaluated in hybrid plants. Plants were transferred in vivo for further estimation (acclimatization, habitus evaluation and tuberization ability).     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Biocontrol of <Emphasis Type="Italic">Pythium</Emphasis> damping-off in cucumber by arbuscular mycorrhiza-associated bacteria from the genus <Emphasis Type="Italic">Paenibacillus</Emphasis>

The Pythium biocontrol features of 17 Paenibacillus strains, all previously isolated from the rhizosphere, hyphosphere or bulk soil from mycorrhizal and non-mycorrhizal cucumber plants, were examined using a cucumber seedling emergence bioassay. Thirteen strains – four strains of Paenibacillus polymyxa, eight strains of P. macerans and one strain of Paenibacillus sp. – significantly increased the percentage of seedling emergence of seeds inoculated with agar plugs of Pythium aphanidermatum FC42. Overall, the efficacy of Pythium biocontrol did not seem to differ between isolates of Paenibacillus originating from either mycorrhizal or non-mycorrhizal systems. No strains significantly reduced the damping-off incidence caused by the aggressive isolate Pythium sp. B5. Two strains of P. macerans not only reduced the incidence of pre-emergence damping-off by 73%, but they also counteracted the plant growth-depressing effect of P. aphanidermatum FC42, so that 68–82% of the emerged seedlings remained healthy 7 days after sowing. Two strains of P. macerans and one strain of P. polymyxa also significantly increased the percentage of seedling emergence following inoculation with approximately 10⁵ zoospores of P. aphanidermatum FC42. There was no significant difference between the dry weight of three selected bacteria-inoculated and -uninoculated plants in the absence of Pythium; however, the dry weight of bacteria-inoculated plants was significantly higher than that of the uninoculated control plants with bacteria in the presence of P. aphanidermatum FC42.     

<Emphasis Type="Italic">Agrobacterium-</Emphasis>mediated transformation of gypsophila (<Emphasis Type="Italic">Gypsophila paniculata</Emphasis> L.)

As a major contributor to the flower market, Gypsophila paniculata is an important target for the breeding of new varieties. However, gypsophila breeding is strongly hampered by the sterility of this species’ genotypes and the lack of a genetic-transformation procedure for this genus. Here we describe the establishment of a transformation procedure for gypsophila (Gypsophila paniculata L.) based on Agrobacterium inoculation of highly regenerative stem segments. The transformation procedure employs stem explants derived from GA₃-pretreated mother plants and a two-step selection scheme. The GA₃ treatment was crucial for obtaining high gene-transfer frequencies (75–90% GUS-expressing explants out of total inoculated explants), as shown using three different gypsophila varieties. An overall transformation efficiency of five GUS-expressing shoots per 100 stem explants was demonstrated for cv. Arbel. The applicability of the transformation system to gypsophila was further reinforced by the generation of transgenic plants expressing Agrobacterium rhizogenes rolC driven by a CaMV 35S promoter. Transgenic gypsophila plantlets exhibited extensive rooting and branching, traits that could be beneficial to the ornamental industry.     

Biocontrol of <Emphasis Type="Italic">Meloidogyne javanica</Emphasis> by <Emphasis Type="Italic">Rhizobium</Emphasis> and plant growth-promoting rhizobacteria on lentil

Biocontrol of the root-knot nematode Meloidogyne javanica was studied on lentil using plant growth-promoting rhizobacteria (PGPR) namely Pseudomonas putida, P. alcaligenes, Paenibacillus polymyxa and Bacillus pumilus and root nodule bacterium Rhizobium sp. Pseudomonas putida caused greater inhibitory effect on the hatching and penetration of M. javanica followed by P. alcaligenes, P. polymyxa and B. pumilus. Inoculation of any PGPR species alone or together with Rhizobium increased plant growth both in M. javanica-inoculated and -uninoculated plants. Inoculation of Rhizobum caused greater increase in plant growth than caused by any species of plant growth-promoting rhizobacteria in nematode-inoculated plants. Among PGPR, P. putida caused greater increase in plant growth and higher reduction in galling and nematode multiplication followed by P. alcaligenes, P. polymyxa and B. pumilus. Combined use of Rhizobium with any species of PGPR caused higher reduction in galling and nematode multiplication than their individual inoculation. Use of Rhizobium plus P. putida caused maximum reduction in galling and nematode multiplication followed by Rhizobium plus P. alcaligens. Pseudomonas putida caused greater root colonization and siderophore production followed by P. alcaligenes, P. polymyxa and B. pumilus. Analysis of the protein bands of these four species by SDS-PAGE revealed that P. putida had a different protein band profile compared to the protein profiles of P. alcaligenes, P. polymyxa and B. pumilus. However, the protein profiles of P. acaligenes, P. polymyxa and B. pumilus were similar.     

Host-related variability in arbuscular mycorrhizal fungal structures in roots of <Emphasis Type="Italic">Hedera rhombea</Emphasis>, <Emphasis Type="Italic">Rubus parvifolius</Emphasis>, and <Emphasis Type="Italic">Rosa multiflora</Emphasis> under controlled conditions

The arbuscular mycorrhizal (AM) morphology of three host plant species inoculated with single and mixed fungal culture and the distribution of AM fungal species in roots of the hosts treated with a mixed culture of AM fungi were determined. The aim was to investigate the effect of host plants and AM fungi on AM morphology of coexisting plant species. Noncolonized rooted cuttings of Hedera rhombea (Miq) Bean, Rubus parvifolius L., and Rosa multiflora Thunb. were inoculated with five fungal species as single and mixed culture inocula. The fungal species used were Gigaspora rosea and Scutellospora erythropa, previously isolated from H. rhombea; Acaulospora longula and Glomus etunicatum from R. parvifolius; and Glomus claroideum from both plant species. A few hyphal and arbusculate coils were seen in the mixed culture-inoculated roots of R. parvifolius; all fungal treatments produced this Paris-type AM in H. rhombea and Arum-type AM in R. parvifolius, and R. multiflora indicates that AM morphology is strongly controlled by the identity of the host plants used in this study. AM fungal rDNA was extracted separately from roots of each replicate plant species inoculated with the mixed fungal culture, amplified, cloned, sequenced, and analyzed to determine the AM fungal species and their respective proportions in roots of each plant species. Glomus etunicatum and G. claroideum of the family Glomaceae generally occurred more frequently in R. parvifolius and R. multiflora, which form Arum-types, whereas S. erythropa, of the family Gigasporaceae, was the most frequently detected species in H. rhombea, which produced Paris-type AM. Although the genotype of the plant species used appears to determine the AM morphologies formed, there was preferential association between the hosts and AM fungal inoculants.     

Synthesis and establishment of <Emphasis Type="Italic">Tuber melanosporum</Emphasis> Vitt. ectomycorrhizae on two <Emphasis Type="Italic">Nothofagus</Emphasis> species in Chile

Axenically germinated seedlings of two species of Southern beech (Nothofagus obliqua, N. glauca) from Chile were inoculated with spores of the Périgord black truffle (Tuber melanosporum). Ectomycorrhizal development was monitored for 6 months in the greenhouse and compared to the performance of the natural host species Quercus ilex and Quercus robur. Seedling survival and mycorrhization showed major differences in both Nothofagus species: T. melanosporum readily formed ectomycorrhizae with seedlings of N. obliqua, although at a lower rate than with Q. ilex but at a proportion very similar to Q. robur; survival and colonization rates were high, and seedling growth was not visibly affected by the high soil pH required by T. melanosporum. In contrast, more than 50% of N. glauca seedlings died after inoculation, and mycorrhiza formation was very sparse. In both species, no colonization by adventive ectomycorrhizal fungi could be observed, whereas both species of Quercus showed minor colonization by another fungus, probably Inocybe or Hebeloma. Our results show that it is possible to infect N. obliqua with the Périgord black truffle under greenhouse conditions, which opens up the possibility of cultivating this truffle as a secondary crop during reforestation with N. obliqua in Chile.     

Heterologous expression of <Emphasis Type="Italic">Vitreoscilla</Emphasis> haemoglobin in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis>)

The vhb gene encoding Vitreoscilla haemoglobin (VHb) was transferred to barley with the aim of studying the role of oxygen availability in germination and growth. Previous findings indicate that VHb expression improves the efficiency of energy generation during oxygen-limited growth, and germination is known to be an energy demanding growth stage during which the embryos also suffer from oxygen deficiency. When subjected to oxygen deficiency, the roots of vhb-expressing barley plants showed a smaller increase in alcohol dehydrogenase (ADH) activity than those of the control plants. This indicates that VHb plants experienced less severe oxygen deficiency than the control plants, possibly due to the ability of VHb to substitute ADH for recycling NADH and maintaining glycolysis. In contrast to previous findings, we found that constitutive vhb expression did not improve the germination rate of barley kernels in any of the conditions studied. In some cases, vhb expression even slowed down germination slightly. VHb production also appeared to restrict root formation in young seedlings. The adverse effects of VHb on germination and root growth may be related to its ability to scavenge nitric oxide (NO), an important signal molecule in both seed germination and root formation. Because NO has both cytotoxic and stimulating properties, the effect of vhb expression in plants may depend on the level and role of endogenous NO in the conditions studied. VHb production also affected the levels of endogenous barley haemoglobin, which may explain the relatively moderate effects of VHb in this study.     

Expression of the <Emphasis Type="Italic">Vicia faba VfPIP1</Emphasis> gene in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> plants improves their drought resistance

Plant aquaporins are believed to facilitate water transport across cell membranes. However, the relationship between aquaporins and drought resistance in plants remains unclear. VfPIP1, a putative aquaporin gene, was isolated from Vicia faba leaf epidermis, and its expression was induced by abscisic acid (ABA). Our results indicated that the VfPIP1 protein was localized in the plasma membrane, and its expression in V. faba was induced by 20% polyethylene glycol 6000. To further understand the function of VfPIP1, we obtained VfPIP1-expressing transgenic Arabidopsis thaliana plants under the control of the CaMV35S promoter. As compared to the wild-type control plants, the transgenic plants exhibited a faster growth rate, a lower transpiration rate, and greater drought tolerance. In addition, the stomata of the transgenic plants closed significantly faster than those of the control plants under ABA or dark treatment. These results suggest that VfPIP1 expression may improve drought resistance of the transgenic plants by promoting stomatal closure under drought stress.     

Priming,signaling, and protein production associated with induced resistance by <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> KPS46

Bacillus amyloliquefaciens KPS46 is a rhizobacterium that induces systemic protection in soybean (Glycine max L.) against several diseases and enhances plant growth. In this study, treatment of soybean seed with KPS46 provided protection to leaves from bacterial pustule, caused by Xanthomonas axonopodis pv. glycines (Xag). KPS46 treatment also increased phenolic content and β-1,3-glucanase and peroxidase activity levels in leaves over non-treated plants. Differential expression of these traits was more rapid and pronounced when KPS46 treated plants were infected with Xag, this pattern indicating priming. Also associated with induced resistance by KPS46 was increased production of salicylic acid (SA) and jasmonic acid (JA) in soybean leaves, suggesting both SA- and JA-dependent signaling pathways are systemically triggered by KPS46 seed treatment. When KPS46 was applied to Arabidopsis roots, however, resistance against Pseudomonas syringae pv. tomato (Pst) was induced only in host genotypes with intact jasmonate, ethylene, and auxin sensitivity. Thus, induced resistance against Pst by KPS46 was SA independent and JA/ethylene dependent. Proteins induced in soybean leaves by KPS46 seed treatment and by the seed treatment in combination with pathogen inoculation were determined by proteomic analysis. Among 20 proteins upregulated in KPS46-treated plants, compared with non-treated plants, only three were defense related. In plants that received both KPS46 treatment and inoculation with Xag, nine of the 20 upregulated protein, as compared with proteins produced Xag inoculated plants having no KPS46 treatment, were defense related. This pattern of increased induction of defense-related proteins following pathogen infection of KPS46 treated plants supported priming by KPS46. Aside from proteins with defense-related function, most of the proteins induced by KPS46 were involved in metabolism and energy conversion, reflecting the strong direct positive effect that KPS46 has on soybean growth.     

<Emphasis Type="Italic">Colletotrichum gloeosporioides</Emphasis> can Overgrow <Emphasis Type="Italic">Colletotrichum kahawae</Emphasis> on Green Coffee Berries First Inoculated with <Emphasis Type="Italic">C. kahawae</Emphasis>

Colletotrichum gloeosporioides is a weak pathogen of coffee that infects ripe berries at dark red stage causing necrotic lesions, but only penetrates up to the second superficial layers of the pericarp at the rose and pink stages. C. kahawae, the causal agent of coffee berry disease (CBD) and responsible for 70–80% of crop loss, infects berries at any stage of development. When green berries are first inoculated with C. kahawae and then at 2, 72 or 96 h later with C. gloeosporioides, the necrotic lesions were significantly larger than in the controls, and were much more evident when the berries were incubated at the optimum growth temperature of 28 °C for C. gloeosporioides. Isolations from the lesions induced by the first inoculations with C. kahawae followed by inoculation with C. gloeosporioides revealed that all or most of the time the recovered isolates of the latter. Thus, C. gloeosporioides can overwhelm C. kahawae under conditions of higher environmental temperature and humidity and may enhance the CBD infection process under field conditions.     

Nutritional suitability and ecological relevance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis> as foodplants for the cabbage butterfly, <Emphasis Type="Italic">Pieris rapae</Emphasis>

The thale cress, Arabidopsis thaliana, is considered to be an important model species in studying a suite of evolutionary processes. However, the species has been criticized on the basis of its comparatively small size at maturity (and consequent limitations in the amount of available biomass for herbivores) and on the duration and timing of its life cycle in nature. In the laboratory, we studied interactions between A. thaliana and the cabbage butterfly, Pieris rapae, in order to determine if plants are able to support the complete development of the herbivore. Plants were grown in pots from seedlings in densities of one, two, or four per pot. In each treatment, one, two, or five newly hatched larvae of P. rapae were placed on fully developed rosettes of A. thaliana. In a separate experiment, the same densities of P. rapae larvae were reared from hatching on single mature cabbage (Brassica oleracea) plants. Pupal fresh mass and survival of P. rapae declined with larval density when reared on A. thaliana but not on B. oleracea. However, irrespective of larval density and plant number, some P. rapae were always able to complete development on A. thaliana plants. A comparison of the dry mass of plants in different treatments with controls (= no larvae) revealed that A. thaliana partially compensated for plant damage when larval densities of P. rapae were low. By contrast, single cress plants with 5 larvae generally suffered extensive damage, whereas damage to B. oleracea plants was negligible. Rosettes of plants that were monitored in spring, when A. thaliana naturally grows, were not attacked by any insect herbivores, but there was often extensive damage from pulmonates (slugs and snails). Heavily damaged plants flowered less successfully than lightly damaged plants. Small numbers of generalist plant-parasitic nematodes were also recovered in roots and root soil. By contrast, plants monitored in a sewn summer plot were heavily attacked by insect herbivores, primarily flea beetles (Phyllotreta spp.). These results reveal that, in natural populations of A. thaliana, there is a strong phenological mismatch between the plant and most of its potential specialist insect herbivores (and their natural enemies). However, as the plant is clearly susceptible to attack from non-insect generalist invertebrate herbivores early in the season, these may be much more suitable for studies on direct defense strategies in A. thaliana.     

Induction of pathogenesis-related proteins during biocontrol of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> with <Emphasis Type="Italic">Pseudomonas aureofaciens</Emphasis> in soybean (<Emphasis Type="Italic">Glycine max</Emphasis> L. Merr.) plants

To investigate the biocontrol effectiveness of the antibiotic producing bacterium, Pseudomonas aureofaciens 63–28 against the phytopathogen Rhizoctonia solani AG-4 on Petri plates and in soybean roots, growth response and induction of PR-proteins were estimated after inoculation with P. aureofaciens 63–28 (P), with R. solani AG-4 (R), or with P. aureofaciens 63–28 + R. solani AG-4 (P + R). P. aureofaciens 63–28 showed strong antifungal activity against R. solani AG-4 pathogens in Petri plates. Treatment with P. aureofaciens 63–28 alone increased the emergence rate, shoot fresh weight, shoot dry weight and root fresh weight at 7 days after inoculation, when compared to R. solani AG-4; P + R treatment showed similar effects. Peroxidase (POD) and β-1,3-glucanase activity of P. aureofaciens 63–28 treated roots increased by 41.1 and 49.9%, respectively, compared to control roots. POD was 26% greater in P + R treated roots than R. solani treated roots. Two POD isozymes (59 and 27 kDa) were strongly induced in P + R treated roots. The apparent molecular weight of chitinase from treated roots, as determined through SDS-PAGE separation and comparison with standards, was about 29 kDa. Five β-1,3-glucanase isozymes (80, 70, 50, 46 and 19 kDa) were observed in all treatments. These results suggest that inoculation of soybean plants with P. aureofaciens 63–28 elevates plant growth inhibition by R. solani AG-4 and activates PR-proteins, potentially through induction of systemic resistance mechanisms.     

Induction of streptomycin-resistant plantlets in <Emphasis Type="Italic">Solanum surattense</Emphasis> through <Emphasis Type="Italic">in vitro</Emphasis> mutagenesis

The species Solanum surattense Burm.f. has importance in ayurvedic medicine and also as vegetable. Streptomycin-resistant plantlets were induced showing chloroplast encoded mutants in S. surattense from mutagenised (ethyl methane sulphonate and gamma-rays) cotyledon explants. Chloroplast encoded – streptomycin resistant – shoots were developed from green (unbleached) sectors of the cotyledons. The streptomycin-resistant plants were similar to parental plants in morphology and ploidy level (2n=2x=24). Reciprocal crosses between streptomycin-resistant and the original streptomycin sensitive plants have shown the non-Mendelian transmission under the control of chloroplast – DNA. These antibiotic resistant plants are useful in designing biochemical selection schemes aimed at somatic hybrid/cybrid recovery in S. surattense.     

The Use of <Emphasis Type="Italic">Bradyrhizobium</Emphasis> to Enhance Growth and Yield of Soybean in Calcareous Soil in Uzbekistan

In this work the effect of inoculation with Bradyrhizobium japonicum S2492 on soybean (Glycine max (L) Merr) growth, nodulation and yield in nitrogen-deficient soil of Uzbekistan was studied. The field experiments were carried out in Tashkent Province of Uzbekistan in a randomized complete block design with four replicates of each treatment. The results revealed positive effects on growth, nodule number and yields of soybean after inoculation with B. japonicum S2492. The yield of soybean varieties was 48% higher for inoculated than for uninoculated plants. The effect of the inoculation was specific for variety but not for growth type. The protein and oil contents of seeds also increased after inoculation. It was concluded that B. japonicum S2492 can be considered as a biofertilizer for increasing the productivity of soybean in nitrogen-deficient soils in Uzbekistan.     

Mercury Tolerance of Thermophilic <Emphasis Type="Italic">Bacillus</Emphasis> sp. and <Emphasis Type="Italic">Ureibacillus</Emphasis> sp

Although resistance of microorganisms to Hg(II) salts has been widely investigated and resistant strains have been reported from many eubacterial genera, there are few reports of mercuric ion resistance in extremophilic microorganisms. Moderately thermophilic mercury resistant bacteria were selected by growth at 62 °C on Luria agar containing HgCl₂. Sequence analysis of 16S rRNA genes of two isolates showed the closest matches to be with Bacillus pallidus and Ureibacillus thermosphaericus. Minimum inhibitory concentration (MIC) values for HgCl₂ were 80 μg/ml and 30 μg/ml for these isolates, respectively, compared to 10 μg/ml for B. pallidus H12 DSM3670, a mercury-sensitive control. The best-characterised mercury-resistant Bacillus strain, B. cereus RC607, had an MIC of 60 μg/ml. The new isolates had negligible mercuric reductase activity but removed Hg from the medium by the formation of a black precipitate, identified as HgS by X-ray powder diffraction analysis. No volatile H₂S was detected in the headspace of cultures in the absence or presence of Hg²⁺, and it is suggested that a new mechanism of Hg tolerance, based on the production of non-volatile thiol species, may have potential for decontamination of solutions containing Hg²⁺ without production of toxic volatile H₂S.