Impact of soil water content on maize responses to the plant growth-promoting rhizobacterium Azospirillum lipoferum CRT1

Members of the bacterial genus Azospirillum are root-associated bacteria that increase yield in cereals by promoting growth and alleviating drought stress. How plants integrate the many bacterium-derived growth-promoting stimuli with other environmental factors to generate a coordinated response remains unresolved. Using a commercial Azospirillum strain, A. lipoferum CRT1 and two host maize cultivars, it was observed that bacterization reduced the drought-induced increase in lateral root growth and enhanced the flood-induced increase in lateral root growth in the more drought- and flood-sensitive cultivar. In the other one, A. lipoferum CRT1 only elicited a moderate root growth response under low soil water potential. The photosynthetic potential and activity were increased in the earlier cultivar and decreased in the later one, irrespective of the soil water content. No impact of the bacterium was seen on the growth of the leaves of both cultivars under both stresses until the third leaf stage, therefore suggesting that it is a consequence of multiple primary adaptations to biotic and abiotic stresses. It is suggested that host–bacteria recognition leads to a stress-specific modulation of the root response and a differential stress-independent effect on photosynthesis. This is the first report of the impact of Azospirillum under flood conditions.     

Effect of biocontrol agents and biofertilizers on root rot,yield, harvest index and nutrient uptake of cassava (Manihot esculanta Crantz)

Cassava is an important subsidiary food and industrial raw material in the tropics. Root rot disease, caused by Phytophthora palmivora, poses a serious threat to cassava cultivation in Tamil Nadu, India. Field experiments (2008–09) were conducted to study the effect of biocontrol agents (Trichoderma spp. and Pseudomonas fluorescens) and biofertilizers (Azospirillum, vesicular–arbuscular mycorrhizal fungi and phosphorus-solubilizing bacteria) on root rot, yield, harvest index and nutrient uptake of cassava at two NPK rates. The design of the experiment was a split plot with two NPK rates, recommended and 50% recommended rate, as the main plot treatments and five biocontrol agents and biofertilizers as subplot treatments. The results clearly indicated that use of a bioinoculants consortium significantly reduced root rot infection/disease incidence over uninoculated controls. Azospirillum significantly improved the yield of cassava at 50% of the recommended rate of NPK. NPK rates had no significant impact on harvest index of cassava and Trichoderma and vesicular–arbuscular mycorrhizal fungi resulted in a higher harvest index even at 50% of the recommended NPK rate. Nitrogen, phosphorus and potassium uptake was significantly improved when treated with biofertilizers and/or a consortium.     

Germination of Salicornia bigelovii Ecotypes under Stressing Conditions of Temperature and Salinity and Ameliorative Effects of Plant Growth-promoting Bacteria

Salinity is a major stress condition. Salicornia bigelovii is a valuable edible halophyte, considered to be a promising resource for cultivation in arid coastal zones. Its productivity depends on the supplementary provision of nitrogen, for which an option is chemical fertilization. Nevertheless, indiscriminate use of chemical fertilizers contributes to the problem of increased salinity. The inoculation of plant growth‐promoting bacteria (PGPB) represents an alternative. Seed ecotypes from four coastal areas [Santa Rosa Chica, Santa Rosa Grande, Santa Cruz and Cerro Prieto (CP), Sonora, México] were collected, in order to inoculate them with two species of PGPB (Azospirillum halopraeferens and Klebsiella pneumoniae). Two germination tests were carried out to study the effect of salinity, temperature regime (night/day) and inoculation with PGPB on germination (percentage and rate), plant height, root length and biomass produced (fresh and dry matter). In the first test, all four ecotypes were considered, whereas in the second test only the CP ecotype was involved because it was found to be the outstanding ecotype in the previous test. Results showed inhibition of germination when salinity was higher in all ecotypes except CP. The CP ecotype showed a decrease of seed germination with an increase in NaCl concentrations at all temperatures tested. However, when it was inoculated with both PGPB, the germination percentage was influenced.     

Effect of Azospirillum brasilense inoculation on root morphology and respiration in tomato seedlings

Summary The level of Azospirillum brasilense strain Cd colonization in the rhizosphere of some vegetables was 10⁴–10⁵ colony-forming units (CFU) per root of one plant in 2-week-old plants inoculated with 5 × 10⁸ Azospirillum cells. Significant increases in root length (35%) and in top (90%) and root (50%) dry weight and total leaf area (90%) were observed in 18-day-old inoculated tomato plants compared with non-inoculated controls. An inoculum concentration of 1 × 10⁸ to 5 × 10⁸ CFU/ml stimulated the appearance of root hairs. Large numbers of bacteria (1 × 10⁹ CFU/ml) caused asymmetrical growth of the root tip. In a petri dish system, Azospirillum (1 × 10⁸ CFU/ml) increased root dry weight (150%), protein content (20%), respiration rate per root (70%) and the specific activity of malate dehydrogenase (45%–65%) over non-inoculated controls. The specific respiration rate, expressed as micromol of O₂ per minute per milligram of dry weight of roots, was significantly lower in inoculated roots, suggesting that less energy was spent for accumulation of more dry material.     

2,4-D诱导固氮螺菌在玉米根部结瘤及固氮效果的研究

采用 2 ,4 -D诱瘤法诱导固氮螺菌在玉米根部结人工根瘤并且固氮。最佳的 2 ,4 -D诱瘤浓度为0 9mg/kg。用乙炔还原法和15N2 示踪法均测到了固氮酶活性 ;并且在用乙炔测定固氮酶活性时发现了 4h延迟期的存在。用 2 ,4 -D加固氮螺菌处理的玉米比未加 2 ,4 -D只用固氮螺菌处理的玉米可以忍耐更高的氧压 ,这说明 2 ,4 -D诱发的人工根瘤的形成为固氮螺菌提供了一个屏氧场所     

Single and double inoculation with Azospirillum/Trichoderma: the effects on dry bean and wheat

A plant growth-promoting rhizobacterium (Azospirillum brasilense Sp7) and a bio-control fungus, which can solubilize insoluble phosphorus (Trichoderma harzianum Rifai 1295-22), were evaluated for their single and combined effects on dry bean (Phaseolus vulgaris) and wheat (Triticum aestivum L.) grown in soil. A pot experiment with bean and a field experiment with both bean and wheat were established. In contrast to single inoculation of Trichoderma, the single inoculation of Azospirillum and the double inoculation did not significantly (P >0.05) increase nodule numbers and nodule mass at 45 days after planting in pot grown beans. However, the Azospirillum inoculation with supplementary phosphorus significantly (P <0.05) increased nodule mass. There were no significant (P >0.05) differences among the inoculation treatments for plant dry weight, total plant nitrogen, and total plant phosphorus at 45 days after planting in both pot and field experiments with bean. However, the combined inoculation and rock phosphate application at 1 Mg ha^–1 significantly (P <0.05) increased bean seed yield, total seed nitrogen and phosphorus in the bean field trial. This treatment more than doubled the mentioned properties compared to the control. The microbial inoculations, with the exception of the combined inoculation, significantly (P <0.05) increased total seed nitrogen, but never affected seed yield in the wheat field trial (P >0.05). The combined inoculation improves many plant and yield parameters and, therefore, has some advantages over single inoculation provided that rock phosphate was supplied at an amount not exceeding 1 Mg ha^–1. Higher rock phosphate application rates decreased many plant and yield parameters in our study.This work was carried out at Gaziosmanpaa University, Tokat, Turkey.     

Role of Azospirillum brasilense nitrate reductase in nitrate assimilation by wheat plants

Summary The nitrogen metabolism of wheat plants inoculated with various Azospirillum brasilense strains and nitrate reductase negative (NR^–) mutants was studied in two monoxenic test tube experiments. The spontaneous mutants selected with chlorate under anaerobic conditions with nitrite as terminal electron acceptor fixed N₂ in the presence of 10 mM NO₃ ^– and were stable after the plant passage. One strain (Sp 245) isolated from surface-sterilized wheat roots produced significant increases in plant weight at both NO₃ levels (1 and 10 mM) which were not observed with the NR^– mutants or with the two other strains. Similar effects were observed in a pot experiment with soil on dry weight and total N incorporation but only at the higher N fertilizer level. In the monoxenic test tube experiments plants inoculated with the mutants showed lower nitrogenase activities than NR⁺ strains at the low NO₃ ^– level (1 = mM) but maintained the same level of activity with 10 mM NO₃ ^– where the activity of all NR⁺ strains was completely repressed. The nitrate reductase activity of roots increased with the inoculation of the homologous strains and with the mutants at both NO₃ ^– levels. At the low NO₃ ^– level this also resulted in increased activity in the shoots, but at the high NO₃ ^– level the two homologous strains produced significantly lower nitrate reductase activity in shoots while the mutants more than doubled it. The possible role of the bacterial nitrate reductase in NO₃ ^– assimilation by the wheat plant is discussed.     

Effect of Application of Coir Compost, Enriched Farm Yard Manure and an Hydrophilic Polymer on Soil Moisture Content, Growth and Yield of Rainfed Sorghum in Association with Azospirillum

Field experiment was conducted to study the effect of application of new organic manures and an hydrophilic polymer in combination with fertilizer application and Azospirillum inoculation on soil moisture content, growth and yield of rainfed sorghum. Application of enriched farm yard manure with urea mixed either 24 hours before sowing or at the time of sowing produced the highest LAI, DMP and grain yield. High soil moisture content was noticed due to incorporation of coir compost. Split application of nitrogen and Azospirillum inoculation besides increasing the LAI and DMP gave 15.2 per cent and 14.5 per cent increase in yield respectively.     

Performance of wheat (Triticum aestivum) to incorporation of organic manure and bioinoculants

A field experiment was conducted to evaluate the effect of integrated use of farmyard manure and bio-inoculants on wheat productivity for two years in succession. Increasing levels of farmyard manure (FYM) up to 15 t ha^?1 significantly (p ≤ 0.05) improved the dry matter accumulation, effective tillers per m row length, and grain weight per spike in both the years. Application of 15 t ha^?1 FYM caused significant increase in spikelets per spike and grains per spike over control and 5 t ha^?1 during two consecutive years. Inoculation with MSX-9 strain of Azotobacter chroococcum produced significantly higher dry matter accumulation to 25.63, 13.33, 7.78 and 23.66, 8.35, 5.50% over uninoculation, Azospirillum brasilense (SP-7) and Azospirillum lipoferum (A-5) at harvest during 1999–2000 and 2000–2001, respectively. Incorporation of 15 t ha^?1 FYM significantly (p ≤ 0.05) enhanced grain and straw yield to 62.45 and 38.05%; 56.66 and 36.28%; 59.42 and 37.52% over control in 1999–2000, 2000–2001 and pooled analysis, respectively. The grain and straw yield of wheat significantly (p ≤ 0.05) enhanced to 26.51, 10.10, 7.54 and 14.45, 5.77, 3.16% through A. chroococcum (MSX-9), A. brasilense (SP-7) and A. lipoferum (A-5) over uninoculation.     

Effect of some granular insecticides currently used for the treatment of maize crops (Zea mays) on the survival of inoculated Azospirillum lipoferum

Four insecticides, carbofuran, chlormephos, terbufos and benfuracarb, currently used on maize (Zea mays) at sowing, were tested for their compatibility with Azospirillum lipoferum strain CRT₁ used as an inoculant to improve maize growth and yield. The growth or survival of A lipoferum was studied in the presence of the insecticides: (1) in liquid and solid cultures of the bacteria, (2) when a commercial inoculant (Azogreen‐m?, Liphatech, Meyzieu, France) was inoculated directly on insecticide granules, (3) when inoculated Azogreen‐m granules were mixed with insecticide granules and (4) when inoculated Azogreen‐m granules were delivered separately to the seed bed. Of the four insecticides tested, only terbufos had a slight effect on growth of A lipoferum in solid cultures. All the insecticides decreased the survival of A lipoferum when the bacteria were inoculated directly on to the granules, or when inoculated Azogreen‐m granules were mixed with an insecticide. We hypothesize that the discrepancies between bacterial culture tests and survival studies might be explained by the conditions of desiccation encountered during inoculation of the granules. Desiccation stress could increase the toxic effect of the insecticides. We therefore suggest including desiccation stress in the biotest used to assess inoculant‐pesticide compatibility. © 2001 Society of Chemical Industry