Water stress in cucumber cotyledons infected withXanthomonas campestris pv.cucurbitae

Xanthomonas compestris pv.cucurbitae strain 62 was isolated from diseased cucumber seedlings grown in an open field in Egypt and identified in this study. Inoculation of cucumber seedlings with this strain resulted in reduction of relative water content (RWC) and increase in free proline content of infected cotyledons. RWC was found to be decreased by the increase of disease severity. The reverse was true for free proline content which was found to be increased by the increase of disease severity. These results indicate that water stress increased in direct proportion to the disease severity. Highly significant increase in free proline content was found to occur in organs of cucumber seedlings inoculated with strain 62 and showing disease symptoms on cotyledons only. This implied that water stress was not limited to symptomatic cotyledons but extended to the whole seedling.     

干旱胁迫下覆膜和接种微生物对玉米生长与水分利用效率的影响

针对西北干旱半干旱地区土壤贫瘠与水分缺乏的问题,利用微生物与作物形成互惠互利的共生关系,本研究设置两个水分梯度:干旱胁迫(供试土壤最大持水量的35%)和正常水分(供试土壤最大持水量的75%),两个覆膜方式:无覆膜(NM)和覆膜(FM),4个接种微生物水平:单接AM真菌(AM)、单接解磷细菌(PSB)、联合接种AM真菌与解磷细菌(AM+PSB)以及对照(CK),研究不同水分和覆膜条件下4个接种微生物对玉米生长特性、地上养分吸收与水分利用效率的影响.结果表明: 与正常水分处理相比,干旱胁迫能够显著提高接种AM真菌处理的侵染率,但正常水分处理下土壤根外菌丝密度、总球囊霉素(T-GRSP)与易提取球囊霉素(EE-GRSP)含量明显提高.干旱胁迫下,单接AM真菌处理的促生作用和菌根效应表现最好,能够提高玉米生物量、水分利用效率和土壤有机碳含量,促进土壤N、P、K的吸收与运输,从而增加玉米地上部分N、P、K吸收量;而正常水分下,联合接种AM+PSB处理表现要好于单接AM和PSB处理,且其与覆膜的互作效果最好.相关分析结果表明,玉米生物量、叶片SPAD值和地上部分N、P、K吸收量均与土壤根外菌丝密度呈显著正相关,玉米水分利用效率与其呈显著负相关.     

Use of Agrobacterium expressing green fluorescent protein to evaluate colonization of sonication-assisted Agrobacterium-mediated transformation-treated soybean cotyledons

Colonization and infection of soybean cotyledons by Agrobacterium tumefaciens and subsequent elimination of bacteria from cotyledons were monitored using bacteria expressing green fluorescent protein (GFP). GFP provided a quick, non-destructive method to evaluate, in real time, Agrobacterium colonization of cotyledon surfaces as well as infection of internal cells. GFP was first detected 7 h following inoculation of the cotyledon. By 36 h, GFP expression was very intense, and was limited to the adaxial surface of the cotyledon. Expression of GFP also served as a useful indicator of successful elimination of the bacterium from plant tissue following antibiotic treatment.     

Arbuscular mycorrhizal fungi influence water relations, gas exchange, abscisic acid and growth of micropropagated chile ancho pepper (Capsicum annuum) plantlets during acclimatization and post-acclimatization

Little is known about the role of arbuscular mycorrhiza fungi (AMF) on physiological changes of micropropagated plantlets during acclimatization and post-acclimatization. Using chile ancho pepper (Capsicum annuum L. cv. San Luis), measurements were made of water relations, gas exchange, abscisic acid (ABA), plantlet growth and AMF development. Plantlets had low photosynthetic rates (A) and poor initial growth during acclimatization. Relative water content (RWC) decreased during the first days after transfer from tissue culture containers to ex vitro conditions. Consequently, transpiration rates (E) and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional and able to respond ex vitro to partial desiccation--thus avoiding excessive leaf dehydration and plant death. Colonization by AMF occurred within 3 days after inoculation. Colonized plantlets had lower leaf ABA and higher RWC than noncolonized (NonAMF) plantlets during peak plant dehydration (6 days after plant transfer)--and a higher A and gs as early as days 5 and 7. During post-acclimatization [after day 8, when RWC increased and stabilized], A increased in all plantlets; however, more dramatic changes occurred with AMF plantlets. Within 48 days, 45% of the roots sampled of inoculated plantlets were colonized and had extensive arbuscule development. At this time, AMF plantlets also had greater E, A, leaf chlorophyll, leaf elemental N, P and K, leaf dry biomass and leaf area, fruit production and differences in carbon partitioning [lower root/shoot ratio and higher leaf area ratio] compared with NonAMF plantlets. Rapid AMF colonization enhanced physiological adjustments, which helped plantlets recover rapidly during acclimatization and obtain greater growth during post-acclimatization.     

Stimulation of the ionic transport system in Brassica napus by a plant growth-promoting rhizobacterium (Achromobacter sp.)

A plant growth-promoting rhizobacterium belonging to the genus Achromobacter was isolated from the oil-seed-rape (Brassica napus) root. Growth promotion bioassays were performed with oilseed rape seedlings in a growth chamber in test tubes containing attapulgite and mineral nutrient solution, containing NO3- as N source. The presence of this Achromobacter strain increased shoot and root dry weight by 22-33% and 6-21%, respectively. Inoculation of young seedlings with the Achromobacter bacteria induced a 100% improvement in NO3- uptake by the whole root system. Observations on the seminal root of seedlings 20 h after inoculation showed that there was an enhancement of both the number and the length of root hairs, compared to non-inoculated seedlings. Electrophysiological measurements of NO3- net flux with ion-selective microelectrodes showed that inoculation resulted in a specific increase of net nitrate flux in a root zone morphologically similar in inoculated and non-inoculated plants. The root area increased due to root hair stimulation by the Achromobacter bacteria, which might have contributed to the improvement of NO3- uptake by the whole root system, together with the enhancement of specific NO3- uptake rate. Moreover, inoculated plants showed increased potassium net influx and proton net efflux. Overall, the data presented suggest that the inoculation of oilseed-rape with the bacteria Achromobacter affects the mineral uptake.     

Arbuscular mycorrhizal symbiosis alleviates drought stress imposed on Knautia arvensis plants in serpentine soil

Background and Aims

Plants growing on serpentine bedrock have to cope with the unique soil chemistry and often also low water-holding capacity. As plant-soil interactions are substantially modified by arbuscular mycorrhizal (AM) symbiosis, we hypothesise that drought tolerance of serpentine plants is enhanced by AM fungi (AMF).

Methods

We conducted a pot experiment combining four levels of drought stress and three AMF inoculation treatments, using serpentine Knautia arvensis (Dipsacaceae) plants as a model.

Results

AMF inoculation improved plant growth and increased phosphorus uptake. The diminishing water supply caused a gradual decrease in plant growth, accompanied by increasing concentrations of drought stress markers (proline, abscisic acid) in root tissues. Mycorrhizal growth dependence and phosphorus uptake benefit increased with drought intensity, and the alleviating effect of AMF on plant drought stress was also indicated by lower proline accumulation.

Conclusions

We documented the role of AM symbiosis in plant drought tolerance under serpentine conditions. However, the potential of AMF to alleviate drought stress was limited beyond a certain threshold, as indicated by a steep decline in mycorrhizal growth dependence and phosphorus uptake benefit and a concomitant rise in proline concentrations in the roots of mycorrhizal plants at the highest drought intensity.     

Arbuscular mycorrhizal symbiosis regulates the physiological responses,ion distribution and relevant gene expression to trigger salt stress tolerance in pistachio

Mycorrhizal symbiosis is generally considered effective in ameliorating plant tolerance to abiotic stress by altering gene expression, and evaluation of genes involved in ion homeostasis and nutrient uptake. This study aimed to use arbuscular mycorrhizal fungus (AMF) to alleviate salinity stress and analyse relevant gene expression in pistachio plants under No/NaCl stress in greenhouse conditions. Arbuscular mycorrhizal symbiosis was used to study the physiological responses, ion distribution and relevant gene expression in pistachio plants under salinity stress. After four months of symbiosis, mycorrhizal root colonization showed a significant reduction in all tested parameters under salt stress treatment compared to non-saline treatment. Salinity affected the morphological traits, and decreased the nutrient content including N, P, Mg and Fe as well as K/Na and Ca/Na ratios, relative water content (RWC), membrane stability index (MSI), and increased the concentration of K, Ca and Na nutrient, glycine betaine, ROS and MDA. Inoculation of seedlings with AMF mitigated the negative effects of salinity on plant growth as indicated by increasing the root colonization, morphological traits, glycine betaine, RWC and MSI. Specifically, under salinity stress, shoot and root dry weight, P and Fe nutrient content, K/Na and Ca/Na ratio of AMF plants were increased by 53.2, 48.6, 71.6, 60.2, 87.5, and 80.1% respectively, in contrast to those of the NMF plants. The contents of Na, O^2•− and MDA in AMF plants were significantly decreased by 66.8, 36.8, and 23.1%, respectively at 250 mM NaCl. Moreover, salinity markedly increased SOS1, CCX2 and SKOR genes expression and the inoculation with AMF modulated these genes expression; however, NRT2.4, PHO1 and PIP2.4 gene expressions were increased by salinity and AMF. It could be concluded that inoculation of AMF with Rhizophagus irregularis conferred a larger endurance towards soil salinity in pistachio plants and stimulate the nutrient uptake and ionic homeostasis maintenance, superior RWC and osmoprotection, toxic ion partitioning, maintaining membrane integrity and the ion-relevant genes expression.     

Enhanced secondary metabolite (tanshinone) production of <Emphasis Type="Italic">Salvia miltiorrhiza</Emphasis> hairy roots in a novel root–bacteria coculture process

Salvia miltiorrhiza Bunge (Lamiaceae) hairy root cultures were inoculated (at 0.02 and 0.2% v/v) and co-cultured with Bacillus cereus bacteria. The root biomass growth was inhibited significantly by the bacteria inoculated to the root culture on the first day (day 0) but not by the bacteria inoculated on days 14 or 21 (in a 28-day overall period). On the other hand, the growth of the bacteria in the hairy root culture was also strongly inhibited by the hairy roots, partially because of the antibacterial activity of the secondary compounds produced by the roots. Most interestingly, the tanshinone production was promoted by the inoculation of bacteria at any of these days but more significantly by an earlier bacteria inoculation. With 0.2% bacteria inoculated on day 0, for example, the total tanshinone content of roots was increased by more than 12-fold (from 0.20 to 2.67 mg g⁻¹ dry weight), and the volumetric tanshinone yield increased by more than sixfold (from 1.40 to 10.4 mg l⁻¹). The tanshinone production was also stimulated by bacterial water extract and bacterial culture supernatant but less significantly than by the inoculation of live bacteria. The results suggest that the stimulation of tanshinone production by live bacteria in the root cultures may be attributed to the elicitor compounds originating from the bacteria, and the hairy root–bacteria coculture may be an effective strategy for improving secondary metabolite production in plant tissue cultures.     

The role of aquaporin RWC3 in drought avoidance in rice

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.     

Enzymes regulating the accumulation of active oxygen species during the hypersensitive reaction of bean to Pseudomonas syringae pv. phaseolicola

Changes in the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7) and catalase (CAT; EC 1.11.1.6) which regulate the persistence of active oxygen species (AOS) were examined in leaves of bean (Phaseolus vulgaris L. cv. Tendergreen) undergoing compatible and incompatible interactions to race 6 and race 3 strains, respectively, of the halo-blight bacterium Pseudomonas syringae pv. phaseolicola. Resistance of cv. Tendergreen to race 3 is determined by the R3 gene and was expressed by a hypersensitive reaction (HR) which was associated with a rapid increase in lipid peroxidation between 8 and 12 h after inoculation. Five main isoforms of SOD were resolved by native polyacrylamidegel electrophoresis (PAGE). Major changes were found in the activities of the cytosolic Cu, Zn-SOD3 and Cu, ZnSOD5 isoforms, which increased by 6 h after inoculation with race 3, and the possibly peroxisomal MnSOD2 isoform, which decreased rapidly in tissue undergoing the HR. Three further minor isoforms of SOD showed a strong increase in activity during the HR. A low level of extracellular SOD activity was also resolved; two isoforms, one of which increased dramatically in activity during the HR, were detected within intercellular fluids recovered from inoculation sites. Fewer changes in SOD activities were found during the compatible interaction to race 6, and they did not occur until 16 h after inoculation. In tissue around infiltration sites, no decrease in the activity of Mn-SOD2 was observed but slight increases in some other isoforms were found. Four groups of POD isoforms were detected in both 3,3-diaminobenzidine/H₂O₂-and o-dianisidine/H₂O₂-stained PAGE gels. Significant changes in activity were again associated with development of the HR. In particular, by 2 h after inoculation, increases in POD3a, b and c isoforms were detected within total soluble extracts and also in POD3c within intercellular fluids (no other isoform was found in the apoplasm). By contrast, POD1 and POD2 activities generally declined following inoculation. The principal change in activity in tissues surrounding infiltration sites was an increase in POD3 isoforms following inoculation with race 3. Measurements of total activity showed a decrease in CAT activity as early as 2 h after inoculation, followed by a recovery after 8 h and a further decrease as infiltrated tissue collapsed during the HR. A more-gradual decline in CAT activity was observed at sites undergoing the compatible interaction and also in tissue surrounding inoculation sites. The spatial and temporal changes detected in activities of CAT and isoforms of SOD and POD clearly demonstrate the complexity and potential subtlety of control of the production and persistence of AOS in bean following microbial challenge. The generation of AOS through HR-specific, early increases in extra-cellular POD and SOD isoforms is discussed.This work was supported in part by the scientific Research Foundaation (OTKA F 5082), the foundation for Hungarian science, a british council scolership to A.L.A and the U.K. Agricultural and food Reaserch council.     

Salicylic acid mediated by the oxidative burst is a key molecule in local and systemic responses of cotton challenged by an avirulent race of Xanthomonas campestris pv malvacearum

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(.-)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mM. Infiltration of 2 mM SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2. 5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(.-)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(.-). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons.     

Association between N2-fixing bacteria and pearl millet plants: Responses,mechanisms and persistence

Responses to inoculation with N₂-fixing bacteria were studied in relation to genotypic differences in pearl millet, effect of nitrogen levels, and FYM additions in India. In some experiments, inoculation increased mean grain yield up to 33% over the uninoculated control, whereas in the remaining 11 experiments there was no significant increase. Increased grain yields, >10% over the uninoculated controls were observed in 46% of the experiments withAzospirillum lipoferum (18.7% average increase) and withAzotobacter chroococcum (13.6% average increase). Yield increases were nil or reduced in three experiments withAzos. lipoferum and four experiments withAztb. chroococcum. In two experiments continued inoculation for two or three years resulted in increased grain, plant biomass yield, and N uptake. Interactions of bacterial cultures with cultivars or years were not observed. The counts of the inoculated strains increased two to three-fold when inoculation was continued for three years. Repeated inoculations increased the mean cumulative N uptake from season 1 to season 3 by 19 kg ha^–1. Repeated inoculations withAztb. chroococcum andAzos. lipoferum increased mean grain yield of a succeeding crop by 14.4% and 9.8%, respectively, over the uninoculated control. Inoculation increased the efficiency of N-assimilation by pearl millet. Marginal increase in nitrogenase activity, associated with the inoculated plants was observed during later stages of plant growth. Increased leaf nitrate reductase activity (NRA) was observed after inoculation with these bacteria. The responses to inoculation are mainly attributable to increased plant N assimilation which could be the effect of growth promoting substances secreated by the bacteria; and thus the contribution from BNF may be small.CRISAT, journal article 732.     

Impact of soil sterilization and irrigation intervals on P and K acquisition by mycorrhizal onion (<Emphasis Type="Italic">Allium cepa</Emphasis>)

Drought is a world-spread problem seriously influencing crop production. Arbuscular mycorrhizal (AM) association and soil microorganisms can help plant growth under water stress condition by improvement of its nutrient and water uptake. In this experiment, onion plants (Allium cepa L. cv. Red Azar Shahr) were inoculated with three AM fungi species (Glomus versiforme, G. intraradices, G. etunicatum) or left un-inoculated as non-mycorrhizal plants, in a sterile or non-sterile sandy loam soil. Plants were irrigated at 7, 9 or 11-day intervals to keep the soil moisture content to field capacity at the irrigation time. Mycorrhizal root colonization decreased (p < 0.05) with an increase in irrigation interval, and the highest root colonization was achieved at 7-day irrigated onions in symbiosis with G. versiforme. Phosphorus content in plant tissue was significantly increased in mycorrhizal than non-mycorrhizal onions. Plants inoculated with G. versiforme at 9-day interval treatment had the highest leaf P content, while the lowest P was observed in non-mycorrhizal plants at all irrigation intervals. Onions inoculated by G. versiforme or G. etunicatum at 9-day irrigation interval had the highest K content. Results revealed that the inoculation of onion plant with G. versiforme or G. etunicatum and increasing irrigation interval up to 9 days, could improve P and K uptake.     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

Technical approaches to inoculate micropropagated sugar cane plants were Acetobacter diazotrophicus

Micropropagated plantlets of sugar cane were inoculated with the N2-fixing bacterium Acetobacter diazotrophicus. Various modifications on the basic plant culture medium MS were made for the plant/bacteria association. The protocol required the inoculation of the bacteria at the end of the rooting period in a medium without hormones or vitamins, and with the concentration of sugar and mineral nutrients reduced by a factor of 10. Individual plants were inoculated with A. diazotrophicus and maintained under the appropriate light and temperature condition used for micropropagation up to 7 days. The system favored the infection and the establishment of the bacteria within the plant tissue. Bacteria colonized the plant tissue and accumulated in inter-cellular cavities and the region of lateral root emergence and also colonizes the xylem vessels. The inoculated plantlets were subsequently transferred to the acclimatization phase and after 30 days it was possible to isolate the bacteria from plant tissue. This protocol permitted studies of infection and comparison among strains.     

Comparative analysis of induction pattern of programmed cell death and defense-related responses during hypersensitive cell death and development of bacterial necrotic leaf spots in eggplant

Pseudomonas cichorii causes necrotic leaf spots (NLS), while Pseudomonas syringae pv. tabaci induces a hypersensitive response (HR) in eggplant. P. cichorii induced cell death at 9 h after inoculation (HAI), reaching a maximum of around 24–30 HAI. On the other hand, cell death was induced 6 HAI with P. syringae pv. tabaci, reaching a maximum of around 12–18 HAI. Superoxide generation was observed in eggplant inoculated with both bacteria. DNA fragmentation, cytochrome c release into the cytosol and expression of defense-related genes such as PR-1 and hsr203J was also induced by inoculation with both bacteria, but these plant reactions were more rapidly induced in eggplant inoculated with P. syringae pv. tabaci rather than those with P. cichorii. Lipid peroxidation and induction of lipoxygenase (LOX) was drastically induced in eggplant inoculated with P. syringae pv. tabaci compared to P. cichorii-inoculated eggplant. Pharmacological studies showed that induction of the cell death, and the NLS or the HR in response to both bacteria was commonly associated with de novo protein synthesis, reactive oxygen species and caspase III-like protease. Interestingly, involvement of lipid peroxidation, LOX, serine protease, and DNase differed between induction of NLS and HR. These results suggest that programmed cell death might be closely associated not only with the HR but also NLS. However, there may be differences not only in the induction kinetics and level of plant responses but also in the infection-related responses between HR and NLS.     

Agrobacterium tumefaciens-mediated transformation of Pinus pinea L. cotyledons: an assessment of factors influencing the efficiency of uidA gene transfer

 This study is the first report of a protocol for transfer and expression of foreign chimeric genes into cotyledons excised from Pinus pinea L. embryos. Agrobacterium tumefaciens EHA105 harbouring the plasmid p35SGUSint was more infective than LBA4404 or C58 GV3850, as determined by the percentage of cotyledons showing uidA expression. Factors which significantly affected the T-DNA transfer included: (1) preinduction and concentration of bacteria, (2) days of coculture and (3) the wounding procedure applied. More efficient transfer of the uidA gene was achieved growing the bacteria in YEP medium at pH 7, infecting the cotyledons according to the sonication-assisted Agrobacterium-mediated transformation procedure with a bacterial density of 1 (OD_600 nm) for 5 min, and coculture for 72 h. Using this protocol, 49.7% of the cotyledons showed a diffuse blue staining 7 days after infection. However, all were necrotic 30 days after inoculation. Since a decrease in bacterial density to 0.01 allowed the recovery of about 4% of cotyledons forming buds 1 month after inoculation, we conclude that the high mortality associated with the infection may be related to the hypersensitive response of the plant to bacterial infection. Received: 19 October 1998 / Revision received: 18 February 1999 / Accepted: 24 February 1999     

Arbuscular mycorrhizal fungi and biochar improves drought tolerance in chickpea

Arbuscular mycorrhizal fungi (AMF) inoculation and biochar amendment has been reported to improve growth of several crop plants however their role in stress amelioration individually as well as in combination has not been worked out. This experiment was conducted to evaluate the application of AMF and biochar on the performance of chickpea under drought stress. The treatments included the individual as well as combined treatment of AMF and biochar to drought stressed and normal chickpea plants. Plants inoculation improved growth in terms of shoot and root length, leaf area and number of branches which was observed to show a steep decline due to drought stress. Drought declined the AMF colonization potential though biochar amendment ameliorated the negative effects of drought significantly by improving the spore population, number of mycelium, vesicle and arbuscules and the percentage of colonization as well. Increased chlorophyll synthesis in biochar and AMF treated plants was obvious, which lead to significant enhancement in the net photosynthetic efficiency. Drought stress also declined the relative water content (RWC) and membrane stability index (MSI), while treatment of biochar and AMF either individually or in combination mitigated the deleterious effects to considerable extent and caused a significant enhancement in RWC and MSI under normal conditions. Amendments with biochar and AMF inoculation increased the nitrogen fixation attributes including the number and weight of nodules, leghemoglobin content and activity of nitrate reductase enzyme leading to greater uptake and assimilation of nitrogen in them when compared to drought stressed plants. Drought stressed chickpea plants exhibited considerable reduction in uptake of nitrogen and phosphorous which was ameliorated by biochar and AMF treatments. It could be suggested that increase in growth and physiological attributes in chickpea due to biochar amendments and AMF inoculation under drought stress were plausibly due to their involvement in nitrogen and phosphorous uptake, chlorophyll synthesis and photosynthesis.     

Influence of potassium solubilizing microorganism (Bacillus mucilaginosus) and waste mica on potassium uptake dynamics by sudan grass (Sorghum vulgare Pers.) grown under two Alfisols

The main aim of this research was to study the dynamics of K release from waste mica inoculated with potassium solubilizing microorganism (Bacillus mucilaginosus) and to investigate its effectiveness as potassic-fertilizer using sudan grass (Sorghum vulgare Pers.) var Sudanensis as test crop grown under two Alfisols. Results revealed that application of mica significantly enhanced biomass yield, uptake and per cent K recoveries by sudan grass than control (no-K). Biomass yield, uptake and per cent K recoveries increased further when mica was inoculated with bacterial strain in both the soils than uninoculated mica. Alfisol from Hazaribag recorded higher yield, uptake and K recoveries than Alfisol from Bhubaneswar. The dynamics of K in soils indicated that K was released from mica to water-soluble and exchangeable pools of K due to inoculation of mica with Bacillus mucilaginosus in both the soils. Significantly greater amounts of water-soluble, exchangeable and non-exchangeable K were maintained in Alfisol from Hazaribag than Bhubaneswar. Release kinetics of K showed significant release of K from mica treated with bacterial strain. Significant correlation between biomass yield, K uptake by sudan grass and different pools of K in soils were observed. X-ray diffraction analysis indicates greater dissolution of mica due to inoculation of Bacillus mucilaginosus strain in both the soils. Thus, bio-intervention of waste mica could be an alternative and viable technology to solubilize insoluble K into plant available pool and used efficiently as a source of K-fertilizer for sustaining crop production and maintaining soil potassium.