Photosynthesis and transpiration of monterey pine seedlings as a function of soil water suction and soil temperature

Rates of photosynthesis, respiration, and transpiration of Monterey pine (Pinus radiata D. Don) were measured under controlled conditions of soil water suction and soil temperature. Air temperature, relative humidity, light intensity, and air movement were maintained constant. Rates of net photosynthesis, respiration, and transpiration decreased with increasing soil water suction. The decrease in the rates of net photosynthesis and transpiration as a function of the soil temperature at low soil water suctions may be attributed to changes in the viscosity of water. At soil water suctions larger than 0.70 bars rates of transpiration and net photosynthesis may be affected in the same proportion by changes in stomatal apertures.     

Subsoil gravel horizon and maize root growth

Summary A series of factoral experiments involving the effects of gravel concentration in the subsoil horizon, the effect of inter-gravel bulk density, the depth of the surface soil above the gravel horizon and the interaction between soil moisture regime and gravel concentration, on growth and development of maize roots were conducted in the greenhouse. Increasing sub soil gravel concentration decreased the total porosity and the available waterholding capacity. Though the root growth of maize seedlings was adversely affected by gravel concentration above 20 per cent, lower concentration of gravels had a beneficial effect on roots. The root development and the leaf concentration of N, P and K improved with increasing depth of surface soil above the gravel horizon. The symptoms of mechanical impedance, such as thickening of root tips and profuse branching behind the tip were commonly observed on the root axis penetrating the gravelly horizon. re]19750916     

Drought susceptibility of two tomato (Lycopersicum esculentum) varieties

The effects of three levels of moisture under greenhouse conditions and also identical moisture levels under field conditions, on the growth yield and water relations of two tomato cultivars, Fireball and Ife I, were investigated. The objective was to ascertain the drought susceptibility of these two tomato cultivars. The cultivar, Ife I, was more drought susceptible than Fireball and the drought susceptibility increased with the level of soil water stress. The drought tolerance, of Fireball is attributed to a lower leaf area, better root system development in terms of average root length and rooting depth, and a higher leaf water potential. The higher leaf stomatal resistances of Fireball variety suggest an inbuilt mechanism to regulate water vapour flow in times of stress.     

Beneficial bacteria of agricultural importance

The rhizosphere is the soil–plant root interphase and in practice consists of the soil adhering to the root besides the loose soil surrounding it. Plant growth-promoting rhizobacteria (PGPR) are potential agents for the biological control of plant pathogens. A biocontrol strain should be able to protect the host plant from pathogens and fulfill the requirement for strong colonization. Numerous compounds that are toxic to pathogens, such as HCN, phenazines, pyrrolnitrin, and pyoluteorin as well as, other enzymes, antibiotics, metabolites and phytohormones are the means by which PGPR act, just as quorum sensing and chemotaxis which are vital for rhizosphere competence and colonization. The presence of root exudates has a pronounced effect on the rhizosphere where they serve as an energy source, promoting growth and influencing the root system for the rhizobacteria. In certain instances they have products that inhibit the growth of soil-borne pathogens to the advantage of the plant root. A major source of concern is reproducibility in the field due to the complex interaction between the plant (plant species), microbe and the environment (soil fertility and moisture, day length, light intensity, length of growing season, and temperature). This review listed most of the documented PGPR genera and discussed their exploitation.     

Decreased thiamine and magnesium levels in the potentiation of the neurotoxicity of lead in occupational lead exposure

The relationship between blood lead (Pb) and serum levels of calcium and of neural nutrients such as thiamine and magnesium (Mg) has been determined in a Nigerian population that is occupationally exposed to Pb. Forty-seven male Pb workers were recruited as test subjects and 25 males unexposed to Pb served as controls. The test subjects were classified into three groups, based on severity of exposure to Pb. Blood lead (BPb) and the serum levels of Mg, thiamine, and calcium were determined in both test subjects and controls. The mean blood Pb level was not significantly higher in Pb workers. In contrast, Mg and thiamine levels were significantly decreased (p<0.05; p<0.01, respectively). However, the calcium level was not significantly lower in test subjects than in controls. Also, there was a significant negative correlation between serum thiamine and blood Pb levels (r=-0.50; p<0.01). Furthermore, there was a significant negative correlation between serum calcium and BPb levels (r=-0.41; p<0.01). This study has shown that relatively low BPb levels can enhance Pb absorption and also potentiate Pb neurotoxicity in the presence of decreased serum thiamine and Mg levels.     

Plant growth-promoting rhizobacteria do not pose any deleterious effect on cowpea and detectable amounts of ethylene are produced

Summary The use of trap crops such as cowpea could reduce the effects of the root parasitic weed, Striga hermonthica and its subsequent constraints on the growth of cereals. Certain bacteria could augment the trap crop stimulatory effect. We studied the effect of three bacteria introduced to the rhizosphere of three cowpea varieties at planting. Number of days to cowpea flowering was noted and at harvest, data were collected on pod characteristics and biomass. Means of data subjected to ANOVA were compared using Tukey’s Studentized Range Test. We analysed bacterial headspace volatiles for ethylene by gas chromatography and gas chromatography–mass spectrometry. Bacterial type significantly influenced the cowpea varieties with better performance over the non-inoculated control. Average pod weight (g) with bacterial treatment was 37.97 for Enterobacter sakazakii 8MR5, 34.38 for Pseudomonas 44MS8 and 27.46 for Pseudomonas 10M3. Non-inoculated control had an average weight of 20.98 g. Bacteria promoted a significant increase in pod weight (≥30.89%), fresh biomass (≥24.22%), and improved pod number (≥20.54%) and pod wall thickness (≥7.33%) with no deleterious effect on plant health. Ethylene released by the bacteria ranged from trace concentrations in Pseudomonas sp. to 210 nmoles/10⁸ c. f. u./ml in Ent. sakazakii 8MR5.     

Transition of hemoglobin between two tertiary conformations: The transition constant differs significantly for the major and minor hemoglobins of the Japanese quail (Cortunix cortunix japonica)

We demonstrate that 5,5'-dithiobis(2-nitrobenzoate) - DTNB - reacts with only CysF9[93]beta and CysB5[23]beta among the multiple sulfhydryl groups of the major and minor hemoglobins of the Japanese quail (Cortunix cortunix japonica). K(equ), the equilibrium constant for the reaction, does not differ very significantly between the two hemoglobins. It decreases 430-fold between pH approximately 5.6 and pH approximately 9: from a mean of 7+/-1 to a mean of 0.016+/-0.003. Quantitative analyses of the K(equ) data based on published X-ray and temperature-jump evidence for a tertiary structure transition in liganded hemoglobin enable the calculation of K(rt), the equilibrium constant for the r<---->t tertiary structure transition. K(rt) differs significantly between the two hemoglobins: 0.744+/-0.04 for the major, 0.401+/-0.01 for the minor hemoglobin. The mean pK(a)s of the two groups whose ionizations are coupled to the DTNB reaction are about the same as previously reported for mammalian hemoglobins.     

Soil‐dwelling insect pests of tree crops in Sub‐Saharan Africa,problems and management strategies—A review

This review aims to draw the attention of researchers, ecologists and farmers to the threats of soil‐dwelling insect pests on important tree crops in sub‐Saharan Africa, with a special focus on termites. It synthesizes the information on the effects of various factors affecting soil pest occurrence and damage, suggesting that the resultant undesirable effects of soil pests in this region are largely as a result of indiscriminate tree cutting, slash‐and‐burn agriculture and indiscriminate use of pesticides. Major insect orders, their host ranges and the nature of damage on selected tree crops are described. This study further critiques existing soil pest management practices, showing that majority of soil pest management practices are ineffective. Thus, management strategies like “attract and kill” approach based on entomopathogenic fungi need to be studied, developed and emphasized for the management of soil insect pests in sub‐Saharan Africa. A conclusion section attempts to offer suggestions for ways in which future work on soil pests in sub‐Saharan Africa could proceed.     

Potential of <Emphasis Type="Italic">Burkholderia cepacia</Emphasis> RQ1 in the biodegradation of heavy crude oil

The potential of Burkholderia cepacia strain RQ1 in the biodegradation of heavy crude oil (Maya) was assessed to develop an active indigenous bacterial consortium for the bioremediation of crude oil-polluted systems in Nigeria. The heavy crude oil (Maya) was utilized as sole source of carbon, attaining maximum cell densities of 10(8) cfu ml(-1) from an initial 10(5) cfu ml(-1) in 15 days. Biomass also increased with oil concentrations up to 0.8% (w/v). Growth rates ranged from 0.028 h(-1) to 0.036 h(-1) and degradation rates decreased with increasing concentrations of oil from 0.009 day(-1) to 0.004 day(-1). The quantity of oil metabolized increased significantly (P < 0.05) with increasing concentrations of oil. However, the growth of the bacterium was inhibited at crude oil concentrations beyond 6% (w/v). The pH of the culture media also dropped significantly (P < 0.05) during the 15-day test period, while the non-asphaltic fractions of the oil were significantly reduced (by about 89%) during the same period. The bacterium harbours a plasmid of about 10 kb that lacks restriction sites for the endonucleases Asp718, BamHI and PstI.