Zulkifli Shamsuddin

Potential for enhancement of root growth and nodulation of soybean co-inoculated with Azospirillum and Bradyrhizobium in laboratory systems

The potential enhancement of root growth and nodulation in vegetable soybean (AGS190) was studied with application of Azospirillum brasilense (Sp7) and A. lipoferum (CCM3863) co-inoculated with two Bradyrhizobium japonicum strains (TAL102 and UPMR48). Significant root growth stimulation and nodulation were observed in Azospirillum as well as during its co-inoculation with Bradyrhizobium. Nodule formation is linked with the initiation of new roots; nodules were almost absent even in Bradyrhizobium inoculated plant due to the absence of new roots development in clipped rooted seedlings. Total root length, root number, specific root length, root dry matter, root hair development and shoot dry matter were significantly increased by Azospirillum alone and its co-inoculum. Co-inoculated plants significantly influenced the number of nodules and its fresh weight. A. brasilense seemed to perform better in root growth and nodule development compared to A. lipoferum.

Plant Growth-Promoting Rhizobacteria Inoculation to Enhance Vegetative Growth, Nitrogen Fixation and Nitrogen Remobilisation of Maize under Greenhouse Conditions.

Plant growth-promoting rhizobacteria (PGPR) may provide a biological alternative to fix atmospheric N2 and delay N remobilisation in maize plant to increase crop yield, based on an understanding that plant-N remobilisation is directly correlated to its plant senescence. Thus, four PGPR strains were selected from a series of bacterial strains isolated from maize roots at two locations in Malaysia. The PGPR strains were screened in vitro for their biochemical plant growth-promoting (PGP) abilities and plant growth promotion assays. These strains were identified as Klebsiella sp. Br1, Klebsiella pneumoniae Fr1, Bacillus pumilus S1r1 and Acinetobacter sp. S3r2 and a reference strain used was Bacillus subtilis UPMB10. All the PGPR strains were tested positive for N2 fixation, phosphate solubilisation and auxin production by in vitro tests. In a greenhouse experiment with reduced fertiliser-N input (a third of recommended fertiliser-N rate), the N2 fixation abilities of PGPR in association with maize were determined by 15N isotope dilution technique at two harvests, namely, prior to anthesis (D50) and ear harvest (D65). The results indicated that dry biomass of top, root and ear, total N content and bacterial colonisations in non-rhizosphere, rhizosphere and endosphere of maize roots were influenced by PGPR inoculation. In particular, the plants inoculated with B. pumilus S1r1 generally outperformed those with the other treatments. They produced the highest N2 fixing capacity of 30.5% (262 mg N2 fixed plant−1) and 25.5% (304 mg N2 fixed plant−1) of the total N requirement of maize top at D50 and D65, respectively. N remobilisation and plant senescence in maize were delayed by PGPR inoculation, which is an indicative of greater grain production. This is indicated by significant interactions between PGPR strains and time of harvests for parameters on N uptake and at. % 15Ne of tassel. The phenomenon is also supported by the lower N content in tassels of maize treated with PGPR, namely, B. pumilus S1r1, K. pneumoniae Fr1, B. subtilis UPMB10 and Acinetobacter sp. S3r2 at D65 harvest. This study provides evidence that PGPR inoculation, namely, B. pumilus S1r1 can biologically fix atmospheric N2 and provide an alternative technique, besides plant breeding, to delay N remobilisation in maize plant for higher ear yield (up to 30.9%) with reduced fertiliser-N input.

MECHANISM OF ROOT GROWTH AND PROMOTION OF NODULATION IN VEGETABLE SOYBEAN BY AZOSPIRILLUM BRASILENSE

Stimulation of root growth and promotion of nodulation in vegetable soybean (Glycine max) by Azospirillum brasilense was studied under lightroom conditions to understand the possible mechanism of root growth as well as the enhancement of nodule initiation when co-inoculated with Bradyrhizobium. Root growth stimulation of vegetable soybean was positively influenced by the cell-free supernatant of Azospirillum brasilense Sp7 as well as Sp7 itself, and by indole acetic acid (IAA) application. The cell-free supernatant of Sp7 treated plants produced the highest number of roots and root length plant−1 followed by bacterial cells of Sp7 and IAA (log10 9M) application. Control plants were the lowest. The cell-free supernatant of Sp7 may contain growth stimulants similar to IAA, which was responsible for enhanced root growth. Nitrite and nitrate did not show positive role in increasing root growth in vegetable soybean. Co-inoculation of Azospirillum with Bradyrhizobium significantly (P<0.05) promoted nodulation in vegetable soybean. Bradyrhizobium strain UPMR48 performed superior role on promotion of nodule growth by co-inoculation to the strain TAL102. Azospirillum has the potential as a co-inoculant with Bradyrhizobium in vegetable soybean cultivation.

Enhancement in Nutrient Accumulation and Growth of Oil Palm Seedlings Caused by PGPR Under Field Nursery Conditions

Abstract Plant growth promoting rhizobacteria (PGPR) (e.g., Azospirillum and Bacillus spp.) have been reported to enhance growth and fix N2 with several nonleguminous crops. These rhizobacteria have the potential to be applied to oil palm seedlings and, consequently, reduce the cost of nitrogenous fertilizer. The rhizobacteria are also known as a bioenhancer for the ability to increase root growth and enhanced water and nutrient absorption by the host plants. An experiment was carried out in the field nursery station, Federal Land Development Authorities (FELDA), Bukit Mendi, Pahang, Malaysia, to observe the effects of PGPR inoculation on enhanced nutrient accumulation and plant growth (tops and roots) of oil palm seedlings under field nursery conditions. The inoculation process showed positive response in enhancing higher accumulation of nitrogen (N), phosphorus (P), and potassium (K) in the plant tissues, enhanced root dry weight and top growth (dry matter and leaf chlorophyll content) of the host plants under field nursery conditions.

Inoculation of Bacillus sphaericus UPMB-10 to young oil palm and measurement of its uptake of fixed nitrogen using the 15N isotope dilution technique.

There are increasing applications of diazotrophic rhizobacteria in the sustainable agriculture system. A field experiment on young immature oil palm was conducted to quantify the uptake of N derived from N2 fixation by the diazotroph Bacillus sphaericus strain UPMB-10, using the 15N isotope dilution method. Eight months after 15N application, young immature oil palms that received 67% of standard N fertilizer application together with B. sphaericus inoculation had significantly lower 15N enrichment than uninoculated palms that received similar N fertilizers. The dilution of labeled N served as a marker for the occurrence of biological N2 fixation. The proportion of N uptake that was derived from the atmosphere was estimated as 63% on the whole plant basis. The inoculation process increased the N and dry matter yields of the palm leaflets and rachis significantly. Field planting of young, immature oil palm in soil inoculated with B. sphaericus UPMB-10 might mitigate inorganic fertilizer-N application through supplementation by biological nitrogen fixation. This could be a new and important source of nitrogen biofertilizer in the early phase of oil palm cultivation in the field.

Cation Dependence, pH Tolerance, and Dosage Requirement of a Bioflocculant Produced by Bacillus spp. UPMB13: Flocculation Performance Optimization through Kaolin Assays

A bioflocculant-producing bacterial strain with highly mucoid and ropy colony morphological characteristics identified as Bacillus spp. UPMB13 was found to be a potential bioflocculant-producing bacterium. The effect of cation dependency, pH tolerance and dosage requirement on flocculating ability of the strain was determined by flocculation assay with kaolin as the suspended particle. The flocculating activity was measured as optical density and by flocs formation. A synergistic effect was observed with the addition of monovalent and divalent cations, namely, Na+, Ca2+, and Mg2+, while Fe2+ and Al3+ produced inhibiting effects on flocculating activity. Divalent cations were conclusively demonstrated as the best cation source to enhance flocculation. The bioflocculant works in a wide pH range, from 4.0 to 8.0 with significantly different performances (P < 0.05), respectively. It best performs at pH 5.0 and pH 6.0 with flocculating performance of above 90%. A much lower or higher pH would inhibit flocculation. Low dosage requirements were needed for both the cation and bioflocculant, with only an input of 50 mL/L for 0.1% (w/v) CaCl2 and 5 mL/L for culture broth, respectively. These results are comparable to other bioflocculants produced by various microorganisms with higher dosage requirements.

Use of intestinal Pseudomonas aeruginosa in fish to detect the environmental pollutant benzo[a]pyrene

This study examined the potential of Pseudomonas aeruginosa abundance in the intestines of fish as an indicator of exposure to benzo[a]pyrene (BaP). P. aeruginosa populations were enumerated in juvenile African catfish (Clarias gariepinus) injected intramuscularly three days previous with 0, 10, 30, 40, 50 or 70mg/kg of BaP. Hepatic EROD and GST activities and biliary fluorescent aromatic compounds (FACs) 1-OH BaP, 3-OH BaP, 7,8-D BaP and BaP were quantified to investigate agreements between the new indicator and established fish biomarkers. The shape of bacterial population (logarithm of colony-forming unit) dose-response curve generally matched those of biliary FACs concentrations. Conversely, the EROD and GST dose-response curves were generally the mirror images of the bacterial population curve. Changes in intestinal P. aeruginosa population appear to be an indirect effect of BaP exposure because exposure to 0-100μg/ml BaP had no effect on P. aeruginosa populations grown on agar plates containing BaP. Using intestinal P. aeruginosa population of fish as a universal indicator of BaP pollution in aquatic environments is discussed.Conversely, the EROD and GST dose-response curves were generally the mirror images of the bacterial population curve.

The effect of rhizobacterial inoculation on growth and nutrient accumulation of tissue-cultured banana plantlets under low N-fertilizer regime

Banana, an important fruit crop, requires high amounts of N-fertilizers for commercial cultivation. This, however, is costly and can be hazardous to the soil environment when used excessively. Biofertilizer is globally accepted as an alternative source of N-fertilizer and can substantially supplement the N requirement while enhancing the uptake of water and mineral nutrients of crop plants. An experiment was conducted to observe the effect of plant growth promoting rhizobacterial inoculation on growth, nutrient uptake of bananas grown under hydroponics condition. The design of the experiment was randomized complete block with five replicates. The following six treatments were imposed: T1 (control; N0-PGPR), T2: (N0+Sp7), T3: (N0+ UPMB10), T4: (N33%+ Sp7), T5: (N33% + UPMB10), and T6: (N100%-PGPR). The results showed that inoculation by UPMB10 with minimal fertilizer-N supply increased (P < 0.05) the primary root elongation and secondary root initiation and subsequently increased (P < 0.05) the root biomass. The same treatment also increased (P < 0.05) N concentration in pseudostem and leaves and Ca concentration in roots. The total accumulation of N, P, K, Ca and Mg were increased due to inoculation; a consequence of increased plant growth. Plants with this treatment produced an equivalent total dry matter as those supplied with 100% N.

Contribution of legume-N by nodulated groundnut for growth of maize on an acid soil

Abstract A series of glasshouse and field experiments was undertaken to test the hypothesis that intensive cropping of a selected groundnut cultivar inoculated with a compatible and highly effective strain of Bradyrhizobium could contribute substantial amounts of N to the succeeding cereal crops. In the glasshouse experiment, the Bradyrhizobium (strain CB756)-groundnut cultivar (V13) combination produced maximum pod yield and N concentration in the haulm on unlimed and limed soil. An equivalent of 77 kg N ha −1 without lime and 105 kg N ha −1 when limed was estimated to be returned to the soil as legume-N through the groundnut residue. This symbiotic combination was used in a limed (4 t ground magnesium limestone ha −1 ) crop rotation field experiment to estimate the amount of N contributed by groundnut residue as measured by the yield of maize. After 1–3 successive legume crops, an estimated 20–56 kg N ha −1 were contributed to the subsequent maize crops. This accounted for 31 and 37% recovery of the respective total legume-N.

Effects of calcium and aluminium on nodulation, nitrogen fixation and growth of groundnut in solution culture

While considerable information has been presented recently on the alleviating effects of calcium (Ca) on aluminium (Al) toxicity, the interaction between Ca and Al on nodulation and N2-fixation of legumes is little understood. A 28 d solution culture experiment using groundnut (Arachis hypogaea L.) cv. Matjam was conducted to evaluate the effects of four Ca concentrations and four Al levels on nodule development, N2-fixation and plant growth. The Ca concentrations were maintained at 500, 1000, 2500 or 5000 μM, and the sum of activities of monomeric Al species (ΣaAlmono) were 0, 15, 30 and 60 μM. With ΣaAlmono≥30 μM in solution, the time to appearance of the first nodule increased, and, with 60 μM ΣaAlmono in solution, plants remained chlorotic throughout the experiment. Activities≥30 μM reduced nodule number and nodule dry mass per plant, particularly with high (5000 μM) Ca in solution. Also, plant top growth was decreased at ΣaAlmono≥30 μM; the effect only being alleviated by 1000 μM Ca at 30 μM ΣaAlmono. The Ca concentration in the youngest expanded leaf (YEL) increased with increased Ca concentration in solution, but was little affected by Al treatment. Nitrogen concentrations mirrored treatment effects on nodule number and nodule dry mass; Al in solution decreased the N concentration particularly with 5000 μM Ca in solution. Furthermore, increased Ca and Al in solution decreased the Mg concentration in the YEL. This suggested that the absence of any alleviating effect of Ca and Al toxicity (indeed the opposite effect was often observed) resulted from interference in Mg nutrition.