Respiration and microflora of the rhizosphere soil of wheat influenced by foliar application of urea

The numbers of micromycetes and bacteria were investigated with respect to oxygen consumption in the rhizosphere soil of wheat and in non-rhizosphere soil. Plants after foliar application of urea (2 % solution) and non-treated plants were cultivated in degraded chernozem and garden soil in a green-house. Changes in oxygen consumption by the suspensions of rhizosphere and non-rhizosphere soils corresponded to changes in the number of bacteria designated as the rhizosphere effect (R/S). Values of R/S depended on the presence of organic substrates. Changes in oxygen consumption by the soil suspension from the rhizosphere of wheat occurring due to foliar application of urea corresponded to changes in the amount of microflora. The results obtained are discussed with respect to a possible utilization of the data to follow metabolic activity of soils in a natural environment (in situ) determined according to oxygen consumption by a soil suspension, and to assess changes in the microflora of rhizosphere and non-rhizosphere soil.     

Response of two tomato cultivars to field-applied proline under irrigation with saline water: Growth,chlorophyll fluorescence and nutritional aspects

The response of tomato (Solanum lycopersicum L.) to abiotic stress has been widely investigated. Recent physiological studies focus on the use of osmoprotectants to ameliorate stress damage, but experiments at a field level are scarce. Two tomato cultivars were used for an experiment with saline water (6.57 dS m^?1) and subsurface drip irrigation (SDI) in a silty clay soil. Rio Grande is a salinity-tolerant cultivar, while Heinz-2274 is the salt-sensitive cultivar. Exogenous application of proline was done by foliar spray at two concentrations (10 and 20 mg L^?1) during the flowering stage. Control plants were treated with saline water without proline. Proline at the lower concentration (10 mg L^?1) increased dry mass of different plant organs (leaves, stems, and roots) and it improved various chlorophyll a fluorescence parameters compared with controls. Regarding mineral nutrition, K⁺ and P were higher in different organs, while low accumulation of Na⁺ occurred. However, Mg²⁺ was very high in all tissues of Rio Grande at the higher concentration of proline applied. Thus, the foliar spray of proline at 10 mg L^?1 increased the tolerance of both cultivars. The growth of aboveground biomass of Heinz-2274 was enhanced by 63.5%, while Rio Grande improved only by 38.9%.     

Paclobutrazol Improved the Reproductive Growth and the Quality of Seed Oil of Jatropha curcas

Jatropha curcas was treated by soil drench paclobutrazol (PBZ) (0, 2, and 3 g m^?1 of canopy diameter) and foliar spray PBZ (0, 500, 800, and 1,200 ppm). The results showed that PBZ treatments greatly retarded vegetative growth and improved reproductive growth. The lengths of new branches were greatly decreased, whereas the number of fruits per inflorescence, fruit-bearing branches per tree, and total fruit load per tree were increased. Only the 2-g soil drench and the 1,200-ppm foliar PBZ spray significantly increased fruit load. The 2-g soil drench PBZ treatment resulted in a decrease in seed S and Cu contents of J. curcas, whereas Mn and B were greatly or moderately increased. A higher dose (3-g soil drench PBZ) reversed the improvement in reproductive growth and alleviated the negative effects on element contents in seeds compared with the 2-g soil drench PBZ. Finally, soil drench PBZ treatments significantly improved seed oil content and oil quality by reducing the oil acid value, increasing stearic acid and oleic acid contents, and reducing palmitic acid and linoleic acid content. The optimum drench dose was below 2 g m^?1 of canopy diameter. The optimum foliar spray concentration of PBZ was not determined in this study but our results suggest that it is higher than 1,200 ppm.     

Plant growth promoting bacteria from Crocus sativus rhizosphere

Present study deals with the isolation of rhizobacteria and selection of plant growth promoting bacteria from Crocus sativus (Saffron) rhizosphere during its flowering period (October–November). Bacterial load was compared between rhizosphere and bulk soil by counting CFU/gm of roots and soil respectively, and was found to be ~40 times more in rhizosphere. In total 100 bacterial isolates were selected randomly from rhizosphere and bulk soil (50 each) and screened for in-vitro and in vivo plant growth promoting properties. The randomly isolated bacteria were identified by microscopy, biochemical tests and sequence homology of V1–V3 region of 16S rRNA gene. Polyphasic identification categorized Saffron rhizobacteria and bulk soil bacteria into sixteen different bacterial species with Bacillus aryabhattai (WRF5-rhizosphere; WBF3, WBF4A and WBF4B-bulk soil) common to both rhizosphere as well as bulk soil. Pseudomonas sp. in rhizosphere and Bacillus and Brevibacterium sp. in the bulk soil were the predominant genera respectively. The isolated rhizobacteria were screened for plant growth promotion activity like phosphate solubilization, siderophore and indole acetic acid production. 50 % produced siderophore and 33 % were able to solubilize phosphate whereas all the rhizobacterial isolates produced indole acetic acid. The six potential PGPR showing in vitro activities were used in pot trial to check their efficacy in vivo. These bacteria consortia demonstrated in vivo PGP activity and can be used as PGPR in Saffron as biofertilizers.This is the first report on the isolation of rhizobacteria from the Saffron rhizosphere, screening for plant growth promoting bacteria and their effect on the growth of Saffron plant.     

Exogenous salicylic acid stimulates physiological and biochemical changes to improve growth, yield and active constituents of fennel essential oil

Fennel (Foeniculum vulgare Mill) is a high-value medicinal and essential oil bearing plant used extensively in pharmaceutical, food and cosmetic industries. A pot experiment was carried out in the natural conditions of net house to resolve whether the foliar application of salicylic acid (SA) might enhance the growth, yield and essential oil production of fennel. Plants were sprayed three times with SA. The first spray was carried out at 40?days after sowing (DAS); the second and third sprays were applied one and 2?weeks later, the plants were sprayed with deionised water (control) and different concentrations of SA (10^?5, 10^?4 and 10^?3?M). The foliar spray of SA at 10^?4?M significantly enhanced the vegetative growth (shoot and root lengths, fresh and dry weights), physiological and biochemical characteristics (chl ??a??, chl ??b??, total chlorophyll and carotenoids contents, nitrate reductase activity, carbonic anhydrase activity, leaf-N, -P and -K contents), yield characteristics (number of umbels and fruits, 1,000-seed weight and seed yield) and essential oil yield of fennel. GLC analysis revealed the significant increase in the components of essential oil, viz. trans-anethole (80.4?C84.7?%), methyl chavicol (2.3?C2.5?%) and fenchone (5.6?C7.9?%). It was concluded that foliar spray of SA at 10^?4?M might be employed for enhancing the plant growth as well as yield and quality of essential oil of fennel.     

Deciphering bacterial community variation during soil and leaf treatments with biologicals and biofertilizers to control huanglongbing in citrus trees

The aim of the current study was to gain a clearer understanding of the bacteria involved in different treatments to control huanglongbing in citrus trees. The treatments included additions in soil or on leaf. In soil, there were two treatments, one was addition of biofertilizer mainly consisting of Brevibacillus laterosporus, and another one was the addition of burnt lime. On leaf treatment, a plant immunity inducer, Atailing spray, which is a fermented fungal protein product, was used. Besides, there was an integrative treatment including the above additions both in soil and on leaf. The control treatments had no addition. The growth of infected citrus plants was significantly improved by these treatments. We sampled soil under crown circumference, rhizosphere soil and roots, stems and leaves of the citrus trees. Sequencing of the 16S rDNA marker using Illumina methods was applied to determine the bacterial community composition of the samples. The results showed that in the soil samples under crown circumference, treatments increased the relative abundance of the genera Bradyrhizobium and Norank_f__Acidobacteriaceae__Subgroup_1_ compared with the control. In the rhizosphere soil samples, treatments increased the relative abundance of the genus Burkholderia–Paraburkholderia compared with the control. Atailing spray influenced the relative abundance of the bacterial genus norank_f__Acidobacteriaceae__Subgroup_1_ in the rhizosphere soil, as well as Pseudomonas in citrus leaves. Furthermore, 6 months after the treatments, the relative abundance of Actinobacteria and Bacilli at the class level was significantly increased in citrus plant leaves in the group treated with Atailing spray, biofertilizer and burnt lime. Overall, certain bacteria were stimulated by treatments, and the leaf‐associated bacterial communities had important indicators for the health of the citrus endophytic environment. These results provided a theoretical foundation for the development of biological approaches for huanglongbing treatment.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Carotenoid inhibitors reduce strigolactone production and Striga hermonthica infection in rice

The strigolactones are internal and rhizosphere signalling molecules in plants that are biosynthesised through carotenoid cleavage. They are secreted by host roots into the rhizosphere where they signal host-presence to the symbiotic arbuscular mycrorrhizal (AM) fungi and the parasitic plants of the Orobanche, Phelipanche and Striga genera. The seeds of these parasitic plants germinate after perceiving these signalling molecules. After attachment to the host root, the parasite negatively affects the host plant by withdrawing water, nutrients and assimilates through a direct connection with the host xylem. In many areas of the world these parasites are a threat to agriculture but so far very limited success has been achieved to minimize losses due to these parasitic weeds. Considering the carotenoid origin of the strigolactones, in the present study we investigated the possibilities to reduce strigolactone production in the roots of plants by blocking carotenoid biosynthesis using carotenoid inhibitors. Hereto the carotenoid inhibitors fluridone, norflurazon, clomazone and amitrole were applied to rice either through irrigation or through foliar spray. Irrigation application of all carotenoid inhibitors and spray application of amitrole significantly decreased strigolactone production, Striga hermonthica germination and Striga infection, also in concentrations too low to affect growth and development of the host plant. Hence, we demonstrate that the application of carotenoid inhibitors to plants can affect S. hermonthica germination and attachment indirectly by reducing the strigolactone concentration in the rhizosphere. This finding is useful for further studies on the relevance of the strigolactones in rhizosphere signalling. Since these inhibitors are available and accessible, they may represent an efficient technology for farmers, including poor subsistence farmers in the African continent, to control these harmful parasitic weeds.     

Stimulation of in vitro morphogenesis,antioxidant activity and over expression of kaurenoic acid 13-hydroxylase gene in Stevia rebaudiana Bertoni by chlorocholine chloride

Phytoconstituents from medicinal plants are considered as important source of raw materials of drugs for pharmaceutical industries. Biotechnology has become an inevitable approach in the area of research and development of medicinal plants for many decades. The present work has been carried out to ascertain the role of chlorocholine chloride (CCC) on in vitro morphogenesis, antioxidant activity and expression level of kaurenoic acid 13-hydroxylase (KA13H) gene in Stevia rebaudiana. To fulfill these purposes chlorocholine chloride was applied in the Murashige and Skoog (Physiol Plant 15(3):473–497, 1962) medium in combination with other plant growth regulators such as 1-naphthalene acetic acid, kinetin and thidiazuron. Chlorocholine chloride was found to contribute significant role on in vitro morphogenesis of S. rebaudiana as evidenced by the formation of embryogenic calli and increase in callusing and microshooting efficiency of explant, i.e., cotyledonary leaf. Moreover, antioxidant enzyme activity as well as ascorbic acid content of the calli and leaves was also stimulated after application of chlorocholine chloride. Q-PCR amplification using gene-specific primers revealed that CCC also promoted the expression level of KA13H gene in S. rebaudiana leaves. The overall study highlighted the promising role of chlorocholine chloride on regeneration efficiency of cotyledonary leaf, significant promotion in antioxidant potential and expression of KA13H gene in S. rebaudiana.     

普洱地区茶叶内生细菌与根际土壤细菌群落结构分析

[目的]茶叶内生细菌、根际土壤细菌在普洱茶的发酵中起着重要的作用,还可以促进茶树生长,诱导茶树抗病性.研究其群落结构组成及相互关系可为微生物资源开发利用提供理论依据.[方法]本研究以普洱地区茶树叶片和根际土壤为材料,采用高通量测序技术,对茶叶及根际土壤细菌的16S核糖体RNA基因(16S rRNA)进行测序,比较分析茶...     

不同甜叶菊品种叶中绿原酸类成分的比较研究

该文以14个扦插培育的甜叶菊品种叶为材料,从8种不同型号的树脂中筛选出一种合适的大孔吸附树脂对甜叶菊叶中绿原酸类成分进行纯化前处理,采用HPLC法对不同甜叶菊品种叶中所含绿原酸类成分进行比较分析。结果表明:(1)在8种不同型号的树脂中,XAD~(-1)6对甜叶菊叶中绿原酸类成分吸附-解析性能最佳。(2)经优化,上样液浓度1.20 mg·mL~(-1)、样品溶液pH 3、解析液乙醇体积分数70%时XAD~(-1)6树脂对甜叶菊叶中绿原酸类成分具有较好的纯化效果。(3) HPLC检测分析表明,在14个品种中共检测出新绿原酸、绿原酸、隐绿原酸、异绿原酸B、异绿原酸A、异绿原酸C六种绿原酸类成分,其中主要成分均为异绿原酸A、绿原酸、异绿原酸C,而在品种3、5、13、14中没有检测出异绿原酸B。(4) 14个品种中6个绿原酸类成分的含量分别为异绿原酸A 20.55~54.3 mg·g~(-1)、绿原酸17.96~32.93 mg·g~(-1)、异绿原酸C 4.15~19.49 mg·g~(-1)、新原酸0.61~4.61 mg·g~(-1)、隐绿原酸0.52~3.11 mg·g~(-1)、异绿原酸B 0.0~3.17 mg·g~(-1),6种绿原酸类成分总量为43.9~97.8 mg·g~(-1)。可见,不同品种甜叶菊叶中绿原酸类成分含量有明显差异,富含绿原酸类成分的甜叶菊品种可用于开发获取绿原酸类物质。     

Enhanced biomass and steviol glycosides in <Emphasis Type="Italic">Stevia rebaudiana</Emphasis> treated with phosphate-solubilizing bacteria and rock phosphate

Biofertilizers offer alternative means to promoting cultivation of medicinal plants less dependent on chemical fertilizers. Present study was aimed at evaluating the potential of phosphate-solubilizing bacteria (PSB) Burkholderia gladioli MTCC 10216, B. gladioli MTCC 10217, Enterobacter aerogenes MTCC 10208 and Serratia marcescens MTCC 10238 for utilizing Mussoorie rock phosphate (MRP) to enhance plant growth, and stevioside (ST) and rebaudioside-A (R-A) contents of Stevia rebaudiana. The solubilization of MRP by PSB strains varied from 1.4 to 15.2 μg ml⁻¹, with the highest solubilization by Enterobacter aerogenes 10208. The PSB treatment increased the growth and ST and R-A contents of plants. Plant growth and stevioside contents were more pronounced with plants treated with a mixture of strains and grown in MRP amended soil compared to the unamended soil. The increment in shoot length (47.8%), root length (17.4%), leaf dry weight (164%), stem dry weight (116%), total shoot biomass (136%) resulted in enhanced productivity of ST (291%) and R-A (575%) in plants inoculated with mixture of PSB as compared to the uninoculated plants. The soils of PSB treated plants contained more available P than the soils of uninoculated plants (increase of 86–576%). PSB inoculated plants also recorded higher P content (64–273% increase) compared to uninoculated plants. The PSB strains differed in the extent of rhizosphere colonization, carbon source utilization pattern and whole cell fatty acids methyl esters composition.     

Microbial changes in clover rhizosphere after foliar and soil application of cobalt

Application of cobalt(II) nitrate to the leaves of red clover (Trifolium pratense L.) resulted in a pronounced increase of dry weight and the number of root nodules. Counts of bacteria in the rhizosphere, content of ammonia and production of carbon dioxide m rhizosphere soil were also higher, whereas the content of nitrates decreased Differences m the counts of bacteria, aotmomycetes, Azotobaoter, anaerobic bacteria and cellulose decomposing bacteria m the rhizosphere of control and treated plants were not directly related to the way of application of cobalt. GeneraPenicillium, Fusarium andTrichoderma predominated among fungi. The relative occurrence of pemcillia was higher after the application of cobalt, the incidence of fusaria was lower. The effects of foliar and soil application of cobalt on rhizosphere microflora were not identical.     

Sulphur application improves the growth, seed yield and oil quality of canola

Sulphur (S) nutrition is very important for harvesting potential seed and oil yield of rapeseed. This study evaluated response of foliage applied thiourea on the performance of two canola cultivars Shiralee and Dunkeld. Sulphur was applied to soil (40 kg ha^?1) or foliage (500 and 1,000 mg L^?1) at rosette, bud initiation and flowering stages using elemental S or thiourea as source, respectively; no S application was taken as control. Among all the treatments, soil application of S improved the crop growth, yield and oil quality in both cultivars and was followed by foliar application of thiourea at 1,000 mg L^?1 compared with no application. Soil applied S and foliar thiourea (1,000 mg L^?1) delayed the flowering and maturity. Soil and foliar applied S significantly improved leaf area index, crop growth rate, net assimilation rate and chlorophyll contents. Plant height, number of branches, siliqua per plant, seed number per siliqua, 1,000-seed weight, biological and seed yield were also increased by soil applied S and foliage applied thiourea (1,000 mg L^?1). Nonetheless, improvement in harvest index, seed oil, protein and glucosinolate contents was only observed from foliage applied thiourea (1,000 mg L^?1). Response of cv. Shiralee to sulphur application was better than cv. Dunkeld. In conclusion, foliar applied thiourea (1,000 mg L^?1) can have potential to improve growth, yield and oil quality in canola and can be economically viable and attractive alternative source.     

Foliar Paclobutrazol Application Suppresses Olive Tree Growth While Promoting Fruit Set

In some agricultural practices, application of plant growth regulators is very useful as an efficient means to modulate olive tree vigour to optimize fruit production. However, the physiological mechanisms underlying these effects are still poorly understood. Here, we evaluated the effectiveness of paclobutrazol, chlormequat and prohexadione on the modulation of vegetative growth and fruit set, with a special emphasis on the underlying effects exerted by phytohormones, in one-year-old olive trees (Olea europea cv. Arbosana). Paclobutrazol and chlormequat were tested using both foliar spraying and soil irrigation, while prohexadione was applied by foliar spraying only, and all treatments were compared to a control. Among treatments, paclobutrazol and chlormequat were the most effective in promoting vegetative growth retardation, when applied through foliar spray. Growth retardation by foliar application of paclobutrazol was associated with proline accumulation and reduced gibberellin contents in leaves. Furthermore, hormonal profiling revealed that not only all treatments were effective in reducing the endogenous contents of gibberellins, but also that the entire hormonal profiling was altered upon treatments. It is concluded that (i) various plant growth regulators can be effectively used to control olive tree growth, and (ii) paclobutrazol seems to be more efficient on vegetative growth retardation than the other tested treatments, being foliar application more effective than soil treatment.

     

持续干旱对樱桃根际土壤细菌数量及结构多样性影响

以1年生吉塞拉实生容器苗为试材,采用绿色荧光蛋白基因标记技术,研究了干旱胁迫(连续干旱0、7、14、21、28 d和35 d)对樱桃根际促生细菌YT3的标记菌YT3-gfp数量的影响,同时结合平板计数法和末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism,T-RFLP)技术,研究了干旱对樱桃土壤中的微生物数量及细菌群落结构多样性影响。结果表明:樱桃根际土壤中的YT3-gfp数量是非根际土壤中的8.75—28.77倍,随着持续干旱强度的增加,YT3-gfp的数量先增加后减小。干旱对根际土壤中YT3-gfp数量的影响大于对非根际土壤的影响,分别在持续干旱至第21天和28天时,YT3-gfp的数量达到最大值。随着持续干旱强度的增加,根际土壤中细菌和放线菌数量先增加后减小,而真菌的数量一直减少。此外,持续干旱至第21天或28天时,樱桃根际土壤具有最高的丰富度指数、多样性指数和最低的优势度指数。基于T-RFLP的主成分分析结果显示持续干旱14—35 d时,其细菌群落结构成为一个相对独立的群,群落结构趋于多样性;而持续干旱7 d和42 d构成另外两个相对独立的群,群落结构趋于简单。以上分析可知,干旱对土壤微生物影响显著,一定强度的干旱可提高细菌和放线菌数量,提高细菌群落结构多样性,适当干旱对维持根际土壤细菌群落结构多样性是有益的。     

Fate of the Biological Control Agent Pseudomonas aureofaciens TX-1 after Application to Turfgrass

The fate and impact of Pseudomonas aureofaciens TX-1 following application as a biocontrol agent for fungi in turfgrass were studied. The organism was applied with a modified irrigation system by using a preparation containing 1 × 10⁶ P. aureofaciens TX-1 CFU ml⁻¹ about 100 times between May and August. We examined the impact of this repeated introduction of P. aureofaciens TX-1 (which is known to produce the antimicrobial compound phenazine-1-carboxylic acid) on the indigenous microbial community of the turfgrass system and on establishment of introduced bacteria in the soil system. A PCR primer-DNA hybridization probe combination was developed to accurately monitor the fate of P. aureofaciens TX-1 following application in irrigation water. To assess the impact of frequent P. aureofaciens TX-1 applications on the indigenous bacterial community, turfgrass canopy, thatch, and rhizosphere samples were obtained during the growing season from control and treated plots and subjected to DNA extraction procedures and denaturing gradient gel electrophoresis (DGGE). PCR amplification and hybridization of extracted DNA with the P. aureofaciens TX-1-specific primer-probe combination revealed that P. aureofaciens TX-1 not only became established in the rhizosphere and thatch but also was capable of overwintering. Separation of PCR-amplified partial 16S rRNA genes by DGGE showed that the repeated application of P. aureofaciens TX-1 in irrigation water resulted in transient displacement of a leaf surface bacterial community member. There was no obvious alteration of any dominant members of the thatch and rhizosphere microbial communities.     

Prey Range Characterization, Ribotyping, and Diversity of Soil and Rhizosphere Bdellovibrio spp. Isolated on Phytopathogenic Bacteria

Thirty new Bdellovibrio strains were isolated from an agricultural soil and from the rhizosphere of plants grown in that soil. Using a combined molecular and culture-based approach, we found that the soil bdellovibrios included subpopulations of organisms that differed from rhizosphere bdellovibrios. Thirteen soil and seven common bean rhizosphere Bdellovibrio strains were isolated when Pseudomonas corrugata was used as prey; seven and two soil strains were isolated when Erwinia carotovora subsp. carotovora and Agrobacterium tumefaciens, respectively, were used as prey; and one tomato rhizosphere strain was isolated when A. tumefaciens was used as prey. In soil and in the rhizosphere, depending on the prey cells used, the concentrations of bdellovibrios were between 3 × 10² to 6 × 10³ and 2.8 × 10² to 2.3 × 10⁴ PFU g⁻¹. A prey range analysis of five soil and rhizosphere Bdellovibrio isolates performed with 22 substrate species, most of which were plant-pathogenic and plant growth-enhancing bacteria, revealed unique utilization patterns and differences between closely related prey cells. An approximately 830-bp fragment of the 16S rRNA genes of all of the Bdellovibrio strains used was obtained by PCR amplification by using a Bdellovibrio-specific primer combination. Soil and common bean rhizosphere strains produced two and one restriction patterns for this PCR product, respectively. The 16S rRNA genes of three soil isolates and three root-associated isolates were sequenced. One soil isolate belonged to the Bdellovibrio stolpii-Bdellovibrio starrii clade, while all of the other isolates clustered with Bdellovibrio bacteriovorus and formed two distantly related, heterogeneous groups.     

Isolation of phytase-producing bacteria from Himalayan soils and their effect on growth and phosphorus uptake of Indian mustard (Brassica juncea)

Phytase-producing bacteria (PPB) is being investigated as plant growth promoting rhizobacteria (PGPR) to improve the phosphorus (P) nutrition and growth of plants grown in soil with high phytate content. Phytate is dominant organic P forms in many soils and must be hydrolyzed to be available for plants. Indian mustard (Brassica juncea) is a plant with economic importance in agriculture and phytoremediation, therefore biotechnological tools to improve growth and environmental stress tolerance are needed. In this study, we isolated and characterized PPB from Himalayan soils and evaluated their effect on growth and P uptake by B. juncea under greenhouse conditions. Sixty five PPB were isolated and based on phytate hydrolysis, three efficient PPB were chosen and identified as Acromobacter sp. PB-01, Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13. Selected PPB showed ability to grow at wide range of pH, temperature and salt concentrations as well as to harbour diverse PGPR activities, such as: solubilization of insoluble Ca-phosphate (193–642 μg ml^?1), production of phytohormone indole acetic acid (5–39 μg ml^?1) and siderophore. Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13 showed 50 and 70 % inhibition of phytopathogen Rhizoctonia solani, respectively. Greenhouse potting assay also showed that the bacterization of B. juncea seeds with Tetrathiobacter sp. PB-03 and Bacillus sp. PB-13 significantly increased the biomass and P content in 30 days old seedlings. This study reveals the potential of PPB as PGPR to improve the growth of B. juncea.     

The effect of applied sulphur on the growth, grain yield and control of powdery mildew in spring wheat

During the years 1998 and 1999, two field experiments were conducted at the University of Wales, Aberystwyth, UK, to test the effects of soil‐ and foliar‐applied sulphur (S) in spring wheat. S was applied at 0, 20, 40, 60 kg ha^?1 in 1998 and at 60 kg ha^?1 in 1999, using CaSO₄ as a source for the soil application and micronised S (Thiovit, 80%), with and without an organosilicone adjuvant, as a source for the foliar application. Senescence was retarded and grain yield was increased in 1998, following application of foliar S in conjunction with the organosilicone adjuvant. Application of foliar S was associated with a reduction in the level of mildew (Erysiphe graminis) recorded on the upper leaves and ears of the canopy. In 1999, grain yield was unaffected by treatments. A low level of mildew in the crop, particularly on the ears, is thought to be the reason for the lack of response in spite of the fact that senescence was retarded with foliar S application. A combined application of foliar S and commercial fungicide (cyproconazole) to the crop appeared to be more effective at controlling mildew than either S or fungicide applied alone. The study shows that there may be a role for S in a low‐input/organic wheat production system, where there is a need to reduce artificial inputs.