Seasonal dynamics of the association between sweet potato and vesicular-arbuscular mycorrhizal fungi

To better understand the behavior of selected vesicular-arbuscular mycorrhizal (VAM) isolates in the field, we documented the growth of roots, root hairs, and VAM colonization of inoculated and noninoculated sweet potato plants (Ipomea batatas (L.) Lam. cv White Star) over a growing season. We also determined the seasonal dynamics of P and Zn uptake, and shoot and storage-root growth. Shoot cuttings were inoculated with an isolate of either Glomus etunicatum Becker and Gerdemann or Acaulospora rugosa Mortan, or were not inoculated, and were harvested 2, 4, 8, 13, 20, and 27 weeks after planting (WAP). At each harvest, roots were sampled at 0 to 30, 30 to 60, and 60 to 90 cm depths and at 0, 23, 83, and 116 cm from the base of the shoot. At the end of the study, the roots of three non-inoculated plants were sampled by soil horizon. Inoculation had no affect on shoot growth or total shoot uptake of P and Zn; shoot dry mass and P and Z content increased rapidly up to 20 WAP, while shoot length continued to increase through 27 WAP. Shoot-P concentration of plants inoculated with A. rugosa at 2 and 8 WAP were higher than the noninoculated plants, while shoot-Zn concentration was not affected by inoculation. Storage-root yields of inoculated plants were higher than yields for noninoculated plants. Root length density, and percentage of root length with root hairs and VAM colonization were highest and most dynamic near the base of the plant. Percentage of root length colonization by VAM fungi was highest in the E2 horizon, intermediate in the Bh horizon, and lowest in the Ap horizon. Percentage of root length with root hairs had the opposite pattern. Intensive measurements of root characteristics close to the base of the plant, and shoot P-content and concentration during the period of rapid yield production, provided the most useful data for evaluating the activity of effective isolates.Published as Florida Agricultural Experimental Station Journal Series No. R-02576     

Effect of Temperature of the Culture Medium on Growth and Nitrogen Fixation of Inoculated Legumes and Rhizobia

Two pea (Pisum sativum L.) cultivars and a kidney bean (Phaseolus vulgaris L.) cultivars were grown in water cultures at different diurnal temperatures (15, 20, 24, 27, 30°C) or at 10°C night temperature combined with various day temperatures (20, 24, 27, 33 or 35°C) in the root medium. The inoculated plants were, more sensitive to the extreme temperatures than the plants supplied with combined nitrogen (KNO₃). The middle-European pea cv. Violetta was adapted to somewhat higher root temperatures than the northern one cv. Torsdag II, the latter showing better growth at lower temperatures, when the plants were inoculated with the same Finnish Rhizobinm strain (HA1). Especially at optimum day temperatures the nitrogen fixation and consequently the dry weights of the inoculated plants were greatly increased when the night temperature was lowered. The optimum temperature for the growth of free-living Rhizobium strains (HA1 and H43) for peus was found to be 25°C and that of a strain (P103) for beans somewhat higher. Effective nitrogen fixation by nodulated legumes without a supply of combined nitrogen is achieved only when the optimum temperature range for root function is very close to the optimum for the rhizobia.     

Dual inoculation of Fusarium oxysporum endophytes in banana: effect on plant colonization,growth and control of the root burrowing nematode and the banana weevil

The burrowing nematode (Radopholus similis (Cobb) Thorne) and the banana weevil (Cosmopolites sordidus Germar, Coleoptera: Curculionidae) are major pests of banana (Musa spp.) in the Lake Victoria basin region of Uganda. Among biological options to control the two pests is the use of non-pathogenic Fusarium oxysporum Schltdl.: Fries endophytes of banana. We investigated the ability of endophytic F. oxysporum isolates Emb2.4o and V5w2 to control the banana weevil and the burrowing nematode, alone and in combination. Plant colonization by the endophytes was determined by inoculating their chemical-resistant mutants separately and in combination, onto banana roots. Plant growth promotion was determined by measuring plant height, girth, number of live roots and fresh root weight at harvest, and control of the nematode and weevil was determined by challenging endophyte-inoculated plants with the pests 8 weeks after endophyte inoculation. Endophytic root colonization was highest in plants inoculated with both endophytes, compared with those inoculated with only one of the endophytes. Root colonization was better for isolate V5w2 than Emb2.4o. Dually inoculated plants showed a significant increase in height, girth, fresh root weight and number of functional roots following nematode challenge. Nematode numbers in roots were reduced 12 weeks after challenge of 8-week-old endophyte-inoculated plants. Significant reductions in weevil damage were observed in the rhizome periphery, inner and outer rhizomes, compared with endophyte non-inoculated controls. We conclude that dual inoculation of bananas with endophytic isolates Emb2.4o and V5w2 increases root colonization by the endophytes, reduces nematode numbers and weevil damage, and enhances plant growth in the presence of nematode infestation.     

Induced Resistance in the Biocontrol of Pythium aphanidermatum by Pseudomonas spp. on Cucumber

Plants of Cucumis sativus cv. Corona were grown in rockwool, with the root systems split into two separate pots. B pots were treated with water or a cell suspension of Pseudomonas corrugata isolate 13 or P. fluorescens biovar C isolate 15, two rhizosphere isolates effective as biocontrol agents against Pythium aphanidermatum. The P pot was treated with water or a suspension of zoospores of P. aphanidermatum applied at the same time (simultaneous treatment) or 1 week after B pot treatments. Most of the bacterial treatments reduced disease incidence and disease severity. Simultaneous treatment with isolate 15 increased shoot dry weight, leaf area, and number of fruit of inoculated plants in one trial. Some treatments with isolate 13 or 15 also increased root volume or root dry weight in B or P pots, compared to the inoculated plants where the B pot was treated with water only (Pythium control). Lower population densities of P. aphanidermatum in P pots were detected in some treatments to which bacteria were applied to the B pot, but only in the early stages of the experiment. This is the first report of systemic-induced resistance against a root pathogen in cucumber obtained by application of Pseudomonas spp. to a root system spatially separated from the pathogen-inoculated root.     

Differences in the effects of three arbuscular mycorrhizal fungal strains on P and Pb accumulation by maize plants

The effect of arbuscular mycorrhizal (AM) fungi on the accumulation and transport of lead was studied in a pot experiment on maize plants grown in anthropogenically-polluted substrate. The plants remained uninoculated or were inoculated with different Glomus intraradices isolates, either indigenous to the polluted substrate used or reference from non-polluted soil. A considerably lower tolerance to the conditions of polluted substrate was observed for the reference isolate that showed significantly lower frequency of root colonisation as well as arbuscule and vesicule abundance. Plants inoculated with the reference isolate also had significantly lower shoot P concentrations than plants inoculated with the isolate from polluted substrate. Nevertheless, inoculation with either indigenous or reference G. intraradices isolate resulted in higher shoot and root biomass and inoculated plants showed lower Pb concentrations in their shoots than uninoculated plants, regardless of differences in root colonisation. Root biomass of maize plants was divided according to AM-induced colouration into brightly yellow segments intensively colonised by AM fungus and non-colonised or only slightly colonised whitish ones. Intensively colonised segments of the isolate from polluted substrate contained significantly higher concentrations of phosphorus and lead than non-colonised ones, which suggest significant participation of fungal structures in element accumulation. Responsible Editor: Peter Christie.     

Aggressiveness and Damage Potential of Central American and Caribbean Populations of Radopholus spp. in Banana

Monoxenic cultures of burrowing nematode populations extracted from banana roots from Belize, Guatemala, Honduras, and Costa Rica were established on carrot discs. Cultures of Radopholus spp. were also obtained from Florida, Puerto Rico, Dominican Republic, and Ivory Coast. The aggressiveness (defined as reproductive fitness and root necrosis) of these populations was evaluated by inoculating banana plants (Musa AAA, cv. Grande Naine) with 200 nematodes/plant. Banana plants produced by tissue culture were grown in 0.4-liter styrofoam cups, containing a 1:1 mix of a coarse and a fine sand, at ca. 27 °C and 80% RH. Banana plants were acclimated and allowed to grow for 4 weeks prior to inoculation. Plant height, fresh shoot and root weights, root necrosis, and nematode population densities were determined 8 weeks after inoculation. Burrowing-nematode populations varied in aggressiveness, and their reproductive fitness was generally related to damage reported in the field. Plant height and fresh shoot and root weight did not reflect damage caused by nematodes under our experimental conditions. Necrosis of primary roots was closely related to the reproductive fitness of the nematode populations. Variation in aggressiveness among nematode populations followed a similar trend in the two susceptible hosts tested, Grande Naine and Pisang mas. All nematode populations had a low reproductive factor (Rf ≤2.5) in the resistant host except for the Ivory Coast population which had a moderate reproductive factor (Rf ≤ 5) on Pisang Jari Buaya. This is the first report of a burrowing nematode population parasitizing this important source of resistance to R. similis.     

Pathological Reaction of Crested Wheatgrass Cultivars to Four Meloidogyne chitwoodi Populations

Meloidogyne chitwoodi populations from Tulelake, California; Ft. Hall, Idaho; Beryl, Utah; and Prosser, Washington, significantly (P < 0.05) reduced dry shoot weights of crested wheatgrass (Agropyron cristatum L., Gaertn. and A. desertorum, Fisch. ex Link, Schult.) cultivars Hycrest, Fairway, and Nordan in experiments conducted in a greenhouse and growth chamber. Shoot growth depression, root galling, and nematode reproduction indices were greatest (P < 0.05) on plants inoculated with 5,000 eggs/plant. Nematode populations from Tulelake, Ft. Hall, and Beryl significantly (P < 0.05) reduced the growth of the three grass cultivars at 15, 20, 25, and 30 C; the greatest reductions occurred at 20 and 25 C. There were significant differences in the virulence of the nematode populations at high (30 C) and low (15 C) soil temperatures. At 15 C, plant growth was reduced more by the Beryl and Tulelake than by the Ft. Hall population; whereas at 30 C, the Ft. Hall population was more virulent than the Beryl and Tulelake populations. Root galling and nematode reproduction were greater on plants inoculated with Beryl and Tulelake populations at 15 C than on plants inoculated with the Ft. Hall population, while the Ft. Hall population had the most pronounced effects at 30 C.     

Arbuscular mycorrhizal fungi enhance root cadmium and copper accumulation in the roots of the salt marsh plant Aster tripolium L.

It is known that vegetation plays an important role in the retention of heavy metals in salt marshes by taking up and accumulating the metals. In this study, we investigated whether arbuscular mycorrhizal fungi (AMF) increase Cd and Cu uptake and accumulation in the root system of the salt marsh species Aster tripolium L., and whether indigenous AMF isolated from polluted salt marshes have higher capacity to resist and alleviate metal stress in A. tripolium than isolates of the same species originated from non-polluted sites. Plants inoculated with Glomus geosporum, either isolated from a polluted salt marsh site (PL isolate) or from a non-polluted site (NP isolate), and non-mycorrhizal (NM) plants were compared in a pot experiment at four different Cd and Cu concentrations. Cd had no effect in root colonization, whereas high concentrations of Cu decreased colonization level in plants inoculated with the NP isolate. AM colonization did not increase plant dry weight or P concentration but influenced root Cd and Cu concentrations. Inoculation with PL and NP isolates enhanced root Cd and Cu concentrations, especially at highest metal addition levels, as compared to NM plants, without increasing shoot Cd and Cu concentrations. There was no evidence of intraspecific variation in the effects between AMF isolated from polluted and non-polluted sites, since there were no differences between plants inoculated with PL or NP isolate in any of the tested plant variables. The results of this study showed that AMF enhance metal accumulation in the root system of A. tripolium, suggesting a contribution of AMF to the sink of metals within vegetation in the salt marshes.     

Effect of low temperatures on mortality and oviposition in conjunction with climate mapping to predict spread of the root weevil Diaprepes abbreviatus and introduced natural enemies

The tropical root weevil, Diaprepes abbreviatus (L.), has been a pest of citrus and ornamental plants since its introduction into Lake County, FL, in 1964. Since then, it has colonized the Florida peninsula to the south of its point of introduction but has not expanded its range to the north. A lower threshold for oviposition by D. abbreviatus was estimated as 14.9 degrees C. Eggs were highly susceptible to cold, with 95% mortality (LTime95) occurring in 4.2 d at 12 degrees C. Relative susceptibility of life stages to cold was eggs > pupae > larvae > adults. Archived weather data from Florida were examined to guide a mapping exercise using the lower developmental threshold for larvae (12 degrees C) and the lower threshold for oviposition (15 degrees C) as critical temperatures for mapping the distribution of D. abbreviatus and the potential for establishment of egg parasitoids. Probability maps using the last 10 yr of weather data examined the frequency of at least 10, 15, 20, 25, or 30 d per winter when soil temperature was 相似文献   

Yellow leaf spot of cashew: A case of molybdenum deficiency

Summary Rooted cuttings ofSeverinia buxifolia were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungusGlomus intraradices or provided an inoculum filtrate (non-VAM plants) and grown in one of seven media combinations of fired montmorillonite clay (FMC) and Canadian peatmoss (CP) at ratios of 100%, 80%, 67%, 50%, 33%, 20%, or 0% FMC. Mycorrhizal infection increased with higher proportions of FMC, but the growth of both VAM and non-VAM plants was reduced with increased FMC amendment. The growth benefit (top and root fresh-dry weights) conferred by mycorrhizal infection was greater at higher levels of FMC in the media. Improved phosphorus uptake by inoculated severinia plants appeared at least partially responsible for increased growth compared to non-VAM plants under conditions of high soluble salts and pH associated with high FMC composition. Florida Agr. Expt. Sta. Journal Series No. 6319.     

Increased Growth and Yield of Hydroponically Grown Greenhouse Tomato Plants Inoculated with Arbuscular Mycorrhizal Fungi and Fusarium oxysporum f. sp. radicis-lycopersici

The arbuscular mycorrhizal fungi Glomus monosporum, G. vesiculiferum, G. deserticola, G. intraradices, G. mosseae, and two unidentified species were tested to determine their effect on plant growth and fruit production of tomato (Lycopersicon esculentum Mill.) cv. Trust inoculated with Fusarium oxysporum f. sp. radicis-lycopersici (FORL) under near-commercial greenhouse conditions. Inoculation with G. monosporum and G. mosseae significantly increased fruit yield and fruit number of tomato plants grown hydroponically in sawdust. Plant height and plant dry weight increased significantly when inoculated with G. monosporum and G. mosseae. Further, plants inoculated with G. monosporum and G. mosseae showed significantly lower FORL root infection than the untreated control plants.     

Endophytic fungi occurring in fennel, lettuce, chicory, and celery — commercial crops in southern Italy

The occurrence of endophytic fungi in fennel, lettuce, chicory, and celery crops was investigated in southern Italy. A total of 186 symptomless plants was randomly collected and sampled at the stage of commercial ripeness. Fungal species of Acremonium, Alternaria, Fusarium, and Plectosporium were detected in all four crops; Plectosporium tabacinum was the most common in all crop species and surveyed sites. The effect of eight endophytic isolates (five belonging to Plectosporium tabacinum and three to three species of Acremonium) inoculated on lettuce plants grown in gnotobiosis was assessed by recording plant height, root length and dry weight, collar diameter, root necrosis, and leaf yellowing. P. tabacinum and three species of Acremonium, inoculated on gnotobiotically grown lettuce plants, showed pathogenic activity that varied with the fungal isolate. Lettuce plants inoculated with the isolates Ak of Acremonium kiliense, Ac of Acremonium cucurbitacearum, and P35 of P. tabacinum showed an increased root growth, compared to the non-inoculated control. The high frequency of P. tabacinum isolation recorded in lettuce plants collected in Bari and Metaponto, and in fennel plants from Foggia agricultural districts, suggests a relationship not only between a crop species and P. tabacinum, but also between the occurrence of the endophyte and the crop rotation history of the soil.     

Effects of Temperature,Plant Age,Soil Texture,and Meloidogyne incognita on Early Growth of Soybean

A digitizer-microcomputer combination was utilized to determine soybean seedling response to population densities of M. incognita (Mi) under varied environmental conditions. Plant age, temperature, soil texture, and initial Mi inoculum (Pi) influenced the pattern of shoot and root growth. Effects of Mi on plant top growth were evident on plants inoculated 2 days after seeding, but generally were not noticeable on those receiving Mi after 4, 6, or 8 days (observations limited to 6 days after inoculation). The greatest Pi of Mi (16,700 juveniles/plant) suppressed root growth on plants inoculated at 2 or 4 days after seeding. Mi had no impact on root growth at 22 C on plants inoculated 6 or 8 days after seeding at any temperature used (22, 26, 30 C). New root initiation was inhibited on soybeans inoculated 2 days after seeding at the highest Pi at all three temperatures, but only at 30 C for a Pi of 1,670 juveniles/plant. Growth of first order lateral roots and general root length were suppressed by Mi on the youngest (2-day) plants. However, a low Pi (167 juveniles/ plant) resulted in root proliferation on 4-day-old plants at 26 C. Mi was most damaging in a low clay-content soil mixture.     

Artificial Induction and Evaluation of a Mild Isolate of Tomato Spotted Wilt Virus

A severe isolate (BL) of tomato spotted wilt virus (TSWV) that originated from Hawaii was treated with nitrous acid in an effort to obtain mild mutants. The standardized procedure used in mutation experiments was: extracting infected Gomphrena globosa L. leaf tissue in 0.01 M Na₂SO₃, 0.125 M sodium acetate and 0.4 M sodium nitrite at pH 5.5 and incubating the extract for 20 min at room temperature. The extract was inoculated to tobacco (Nicotiana tabacum L. cv. Havana 423) and local lesions were subsequently transferred to lettuce (Lactuca sativa L. cv. Minetto). One isolate (R27G) that incited mild symptoms in lettuce was obtained out of 868 local-lesion-transfers. Under greenhouse conditions, the isolate induced mild symptoms on tomato (Lycopersicon esculentum Mill.) but was severe on peppers (Capsicum annuum L.). The effect of the R27G isolate on growth of potted tomatoes kept outdoors was variable. In one trial, only 15 % of the fruit had symptoms versus 67 % in another trial. R27G fully protected Datura stramonium L. plants that were challenge inoculated with the severe parent BL isolate. Less effective cross protection was observed against a severe isolate from Oklahoma.     

Soil temperature and flooding effects on two species of citrus

Summary Rough lemon (Citrus jambhiri Lush.) and sour orange (C. aurantium L.) seedlings were grown at constant soil temperatures of 16, 24, and 33 C for 3 months. Shoot and root growth of rough lemon was greatest at 33 C while growth of sour orange was greatest at 24 C. There were no significant effects of soil temperature on shoot: root ratio, leaf water potential or stomatal conductance. The hydraulic conductivity of intact root systems of both species was highest when seedlings were grown at 16 C. Thus, acclimation through greater root conductivity at low soil temperature may have compensated for decreased root growth at 16 C and negated effects of soil temperature on plant water relations. Half the plants growing at each soil temperature were subsequently flooded. Within 1 week, the soil redox potential (Eh) dropped below zero mV, reaching a minimum Eh of –250mV after 3 weeks of flooded conditions. Flooded plants exhibited lower root conductivity, a cessation of shoot growth, lower leaf water potentials, lower stomatal conductances, and visual sloughing of fibrous roots. Decreases in root conductivity in response to flooding were large enough to account for the observed decreases in stomatal conductance.Florida Agricultural Experiment Stations Journal Series No. 4080.     

Interactive effects of temperature and arbuscular mycorrhizal fungi on growth,P uptake and root respiration of<Emphasis Type="Italic"> Capsicum annuum</Emphasis> L.

Capsicum annuum (pepper) plants were inoculated with the arbuscular mycorrhizal (AM) fungi Glomus intraradices Smith and Schenck, an undescribed Glomus sp. (AZ 112) or a mixture of these isolates. Control plants were non-mycorrhizal. Plants were grown for 8 weeks at moderate (20.7–25.4°C) or high (32.1–38°C) temperatures. Colonization of pepper roots by G. intraradices or the Glomus isolate mixture was lower at high than at moderate temperatures, but colonization by Glomus AZ112 was somewhat increased at high temperatures. Pepper shoot and root dry weights and leaf P levels were affected by an interaction between temperature and AM fungal treatments. At moderate temperatures, shoot dry weights of plants colonized by the Glomus isolate mixture or non-AM plants were highest, while root dry weights were highest for non-AM plants. At high temperatures, plants colonized by Glomus AZ112 or the non-AM plants had the lowest shoot and root dry weights. AM plants had generally higher leaf P levels at moderate temperatures and lower P levels at high temperatures than non-AM plants. AM plants also had generally higher specific soil respiration than non-AM plants regardless of temperature treatment. At moderate temperatures, P uptake by all AM plants was enhanced relative to non-AM plants but there was no corresponding enhancement of growth, possibly because less carbon was invested in root growth or root respiratory costs increased. At high temperatures, pepper growth with the G. intraradices isolate and the Glomus isolate mixture was enhanced relative to non-AM controls, despite reduced levels of AM colonization and, therefore, apparently less fungal P transfer to the plant.     

Use of chitin for controlling plant-parasitic nematodes

Cabbage plants were grown in soil amended with Clandosan (CLA) prepared from crustacean chitin (0.3% w/w). The plants were maintained in constant temperature tanks set to 15° or 30°C, in soils naturally infested with cyst nematodeHeterodera schachtii, or inoculated with the root-knot nematode,Meloidogyne javanica, respectively. At 30°C, after the first month following inoculation, CLA caused an increase in top fresh weight of plants but no reduction in nematode—induced root galling was recorded. However, when fresh plants were planted, CLA induced a large reduction in gall formation and caused an increase in top fresh weight of nematode-inoculated plants. At 15°C, CLA significantly affected the plants only after 60 days: an increase in top fresh weight and a reduction in the number of eggs per cyst were recorded. Ammonium was not detected in soil after 30 days, at 30°C, whereas at 15°C, CLA-treated soil contained twice as much ammonium as non-treated soil. After 60 days, ammonium was not detected at all. After 30 days nitrate concentrations in soil attained higher values at 30°C than at 15°C, whereas after 60 days high levels were detected only at 15°C. At 30°C, CLA induced an increase in the number of fungi, chitinolytic bacteria, and total amount of bacteria; at 15°C, such an increase was detected only with the chitinolytic microorganisms.Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel No. 2196-E, 1987 series.     

Detection of lectins in nodulated peanut and soybean plants

The direct double-antibody enzymelinked immunosorbent assay system was used in the detection and measurement of seed lectins from peanut (Arachis hypogaea L.) and soybean (Glycine max L.) plants (PSL and SBL, respectively) that had been inoculated with their respective rhizobia. Concentrations of PSL dropped to undetectable levels in peanut roots at 9 d and stems and leaves at 27 d after planting; SBL could no longer be detected in soybean roots at 9 d and in stems and leaves at 12 d. A lectin antigenically similar to PSL was first detected in root nodules of peanuts at 21 d reaching a maximum of 8 g/g at 29 d then decreasing to 2.5 g/g at 60 d. There was no evidence of a corresponding lectin in soybean nodules.Sugar haemagglutination inhibition tests with neuraminidase-treated human blood cells established that PSL and the peanut nodule lectin were both galactose/lactose-specific. Further tests with rabbit blood cells demonstrated a second mannosespecific lectin in peanut nodule extracts that was not detected in root extracts of four-week-old inoculated plants or six-week-old uninoculated plants, although six-week-old root extracts from inoculated plants showed weak lectin activity. The root extracts from both nodulated and uninoculated plants contained another peanut lectin that agglutinated rabbit but not human blood cells. Haemagglutination by this lectin was, however, not inhibited by simple sugars but a glycoprotein, asialothyroglobulin, was effective in this respect.Abbreviations DAS double antibody sandwich - ELISA enzyme-linked immunosorbent assay - PBS phosphate-buffered saline - PSL peanut seed lectin - SBL soybean lectin     

ACC deaminase containing diazotrophic endophytic bacteria ameliorate salt stress in Catharanthus roseus through reduced ethylene levels and induction of antioxidative defense systems

Among a total of 27 cultivable salt tolerant endophytic bacteria isolated from Catharanthus roseus grown in highly salt affected coastal region of cuddalore district, Tamilnadu, India four isolates were found to be positive for nitrogenase activity. The isolates were evaluated for their stress tolerance efficiency and screened for different PGP traits. Based on the above studied parameters, and ability to produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase (4.24???mol ??-ketobutyrate mg^_1 protein h^_1) the salt tolerant diazotrophic isolate AUM54 was selected for further investigation and identified as Achromobacter xylosoxidans by 16S rRNA gene sequencing. The ability of this isolate to ameliorate salt stress in C. roseus was evaluated under gnotobiotic and pot culture conditions. At 150?mM NaCl level A. xylosoxidans AUM54 treated plants recorded ethylene level of 394.1 p mol ethylene g^?1 FW h^?1 compared to the ethylene level of 516.0 p mol ethylene g^?1 FW h^?1 recorded in the un inoculated control. A. xylosoxidans AUM54 inoculated plants recorded the maximum germination percentage of 98.3, vigor index of 2231.4, plant height of 120.4?cm, root dry weight of 53.24?g Plant^_1 and ajmalicine content of 1.60?mg?g^?1, compared to the germination percentage of 91.6%, vigour index of 1511.5, plant height of 105.8, root weight of 47.2?g Plant^?1, and ajmalicine content of 1.23?mg?g^?1 in uninoculated plants grown without NaCl treatment. This isolate also decreased plant ethylene levels by 11?C23% and increased the antioxidative enzyme content of inoculated C. roseus plants to the tune of 19?C32% for ascorbate peroxidase (APX) activity, 20?C30% for superoxide dismutase (SOD) activity and 4?C16% for catalase (CAT) under normal and salt affected conditions.     

Improved Salinity Tolerance of <Emphasis Type="Italic">Arachis</Emphasis><Emphasis Type="Italic">hypogaea</Emphasis> (L.) by the Interaction of Halotolerant Plant-Growth-Promoting Rhizobacteria

Salinity adversely affects plant growth and development. Halotolerant plant-growth-promoting rhizobacteria (PGPR) alleviate salt stress and help plants to maintain better growth. In the present study, six PGPR strains were analyzed for their involvement in salt-stress tolerance in Arachis hypogaea. Different growth parameters, electrolyte leakage, water content, biochemical properties, and ion content were analyzed in the PGPR-inoculated plants under 100 mM NaCl. Three bacterial strains, namely, Brachybacterium saurashtrense (JG-06), Brevibacterium casei (JG-08), and Haererohalobacter (JG-11), showed the best growth of A. hypogaea seedlings under salt stress. Plant length, shoot length, root length, shoot dry weight, root dry weight, and total biomass were significantly higher in inoculated plants compared to uninoculated plants. The PGPR-inoculated plants were quite healthy and hydrated, whereas the uninoculated plant leaves were desiccated in the presence of 100 mM NaCl. The percentage water content (PWC) in the shoots and roots was also significantly higher in inoculated plants compared to uninoculated plants. Proline content and soluble sugars were significantly low, whereas amino acids were higher than in uninoculated plants. The MDA content was higher in uninoculated plants than in inoculated plants at 100 mM NaCl. The inoculated plants also had a higher K⁺/Na⁺ ratio and higher Ca²⁺, phosphorus, and nitrogen content. The auxin concentration was higher in both shoot and root explants in the inoculated plants. Therefore, it could be predicted that all these parameters cumulatively improve plant growth under saline conditions in the presence of PGPR. This study shows that PGPR play an important role in inducing salinity tolerance in plants and can be used to grow salt-sensitive crops in saline areas.