Manipulating legume/cereal mixtures to optimize the above and below ground interactions in the traditional African cropping systems

The purpose of mixing legume and cereals in the cropping systems is to optimise the use of spatial, temporal, and physical resources both above- and below ground, by maximising positive interactions (facilitation) and minimising negative ones (competition) among the components. The complex interactions in legume/cereal cropping systems such as those used by traditional farmers have received little research attention. Information from such studies is likely to provide an understanding of plantsurvival strategies when subjected to stress in mixtures. Current knowledge on how plants in mixtures change their biological and chemical environments and the potential benefits associated with such processes are assessed in this review

The potential roles of lime and molybdenum on the growth, nitrogen fixation and assimilation of metabolites in nodulated legume: A special reference to Phaseolus vulgaris L.

Most soils in sub-Saharan Africa are acidic and have low contents of calcium (Ca2+), magnesium (Mg2+) and molybdenum (Mo). Higher concentrations and contents of hydrogen ion (H+), aluminium (Al3+) and manganese (Mn2+) found in these acidic soils are known to be the major causes of poor plant growth due to their toxicity effects to plants and micro organisms such as N-fixing bacteria. Molybdenum is also a component of some bacterial nitrogenase and therefore, is especially important for plants that live in symbiosis with nitrogen-fixing bacteria such as Rhizobium. Calcium, magnesium and molybdenum deficient plants exhibit poor growth. The most common management practice to ameliorate these acidic soil problems is through the surface application of lime or molybdenum and/ orseed pelleting. The potential role(s) of lime and Mo in legumes with respect to growth, assimilation of metabolites, N-fixation and growth is given special attention in this review

Reclamation of sodic soils in northern Tanzania, using locally available organic and inorganic resources

Sodic soils could produce useful maize (Zea mays L.) crop yields if reclaimed by appropriate techniques. A field experiment was conducted on the selected lowlands of northern Tanzania using a randomised complete block design to study the effectiveness of supplying gypsum (CaSO4.2H2O) or farmyard manure (FMY) alone or both mixtures on the reclamation of a sodic soil. Sodic soil and FYM were characterised to establish their quality status before any intervention was introduced. The treatment used included: control, FYM alone (25 t ha-1), FYM (25 t ha-1) combined with gypsum (12.5 t ha-1) and gypsum alone (12.5 t ha-1). The treatments were replicated four times. Selected numbers of soil physical and chemical properties were then investigated. Results from our study revealed that regardless of the amendments used, maize yield and all soil physical and chemical properties tested were improved in Year 2 (Y2) relative to Year 1 (Y1). Our results also showed that combining FYM with gypsum significantly (p0.05) improved pH, electrical conductivity of the saturated paste (ECe), exchangeable sodium percentage (ESP), infiltration rate (IR), osmotic potential (OP) and available water capacity (AWC) of sodic soils. The FYM was the second-best treatment in the improvement of pH, ESP and EC whereas gypsum was second in the improvement of ESP, IR and maize yield

Biological, ecological and agronomic significance of plant phenolic compounds in rhizosphere of the symbiotic legumes

Phenolics are low molecular compounds ubiquitous in all tissues of higher plants with great significance in plant development. Our understanding of some phenolic compounds in the last few decades has greatly improved. However, their biological, ecological and agronomical significance in therhizosphere of most symbiotic legumes is much less clear. Further understanding of these biomolecules will increase our knowledge of their contribution in soil and water conservation, weed management,mineral element nutrition, their impact as signal molecule in certain symbiotic relationships, and their role as defence molecules against soil pests and pathogens. This article reviews the bioecological and agronomical significance of phenolic compounds in the rhizosphere of a few studied symbiotic legumes and other plants

Effect of the growth retardant Cycocel® in controlling the growth of Dombeya burgessiae

Pink dombeya (Dombeya burgessiae) was tested for its potential as a flowering potted plant, using the growth retardant Cycocel® (2-chloroethyl)-trimethylammonium chloride. The treatments included acontrol, 0.5, 1, 2 and 3 mg/L of Cycocel® per pot and were applied when seedlings reached 7 - 8 cm in height. All treatments significantly reduced plant height. The plants treated with 0.5 mg/L were only marginally shorter than the control, while the height of plants treated with 1, 2 and 3 mg/L Cycocel®, were greatly reduced. Increased Cycocel® concentrations decreased plant width in all treatments, as compared with the control. At all applied concentrations, the deterioration of foliage greenness wasobserved. The highest concentration of Cycocel® (3 mg/L) resulted in cycocel-induced chlorosis. This was followed by the 2, 1 and 0.5 mg/L respectively, all showing symptoms of chlorosis; however to a lesser extent. Cycocel® treated plants exhibited greener foliage in the new leaves formed in the weeks after application compared with the control. It is important to mention that the new leaves formed in the weeks after application were not affected, and were in fact darker green with the higher concentrations of Cycocel® treatments.The fresh and dry weights of plants severely decreased with the increased Cycocel® concentrations. The highest concentration (0.3% a.i.) caused the largest reduction, withplants in this treatment only weighing 38% of the total fresh weight of the control and 35% of the total dry weight

Hydroponic culture of Gladiolus tristis: Application of paclobutrazol for flowering and height control

Gladiolus tristis (ever-flowering gladiolus) was tested for its potential as a flowering potted plant, using the growth retardant paclobutrazol. The treatments included a control, 2, 4, 8 and 16 mg activeingredient (a.i.) per pot and were applied when the longest leaves reached 15 cm. All treatments reduced perpendicular leaf height. Inflorescence heights were significantly affected by paclobutrazol.The flower spikes of plants treated with 2, 4 and 8 mg a.i. per pot were only marginally shorter than the control, while the height of plants treated with 16 mg was significantly reduced. All plants reached firstflower anthesis within a month from 22 weeks after planting. Flowering was staggered throughout the month, from the control through to plants treated with 16 mg a.i., with the control flowering from 166days after planting, gradually increasing to 178 for 2 mg, 181 for 4 mg, 183 for 8 mg, and 186 for 16 mg a.i./pot. The average number of flowers produced per pot significantly dropped with increasing strengthof a.i. applied. The control produced an average of three flowers while plants treated with 16 mg a.i produced less than one

The potential of developing an in vitro method for propagating Strelitziaceae

Strelitzia spp. are highly valued as cut flowers and are of significant commercial value. Despite high demands, they have not been widely spread due to production constraints and are one of the few important cut flower  plants for which no uniform cultivars are available. The conventional methods of propagation are very slow due to the plants low rate of multiplication. Large scale propagation and cloning is therefore needed to exploit its potential. Despite the plants commercial importance, a method for micropropagation has not yet been  established. Tissue culture attempts of this plant have failed due to the oxidative browning of explants.  Wounded tissues release polyphenolic compounds which are detrimental to further development of explants. Only partial success and a low rate of multiplication have been obtained. This review explores the possibilities of developing an in vitro method for the successful propagation of Strelitzia spp.Key words: Strelitzia spp., activated charcoal, antioxidants, auxins, cytokinins, dark incubation, immatureembryos, media composition, wounding

Possible effects of regulating hydroponic water temperature on plant growth, accumulation of nutrients and other metabolites

Water temperature can affect many physiological processes during plant growth and development. Temperatures below or above optimum levels may influence plant metabolic activities positively or negatively. This may include accumulation of different metabolites such as phenolic compounds, reactive oxygen species (ROS), nutrient uptake, chlorophyll pigment formation, the photosynthesis process and finally the growth and development of the plant. The optimum temperature of the growthmedium can contribute to improving and optimising the earlier mentioned plant physiological processes. Information on how the temperature of hydroponic solution influences certain flowering plant production in glasshouses during the winter period is limited. This review suggests the possible benefits of regulating temperatures of the hydroponic solution with the aim of optimising production of flower in the glasshouse during winter periods.Keywords: Chlorophyll, nutrient uptake, phenolic compounds, photosynthesis rate, reactive oxygen specie

Effects of different combinations of Hoagland’s solution and Azolla filiculoides on photosynthesis and chlorophyll content in Beta vulgaris subsp. Cycla ‘fordhook giant’ grown in hydroponic cultures

The assessments of photosynthetic rate, stomatal conductance,  evapotranspiration, intercellular CO2 concentration and chlorophyll content in Beta vulgaris subsp. cycla ‘Fordhook Giant’ grown in hydroponic cultures containing different compositions of hydroponic solutions were evaluated in this study. The aim of the study was to quantify the effects of different combinations of Hoagland’s solution and Azolla filiculoides on photosynthesis processes and chlorophyll content in B. vulgaris grown in hydroponic cultures. The following treatments were evaluated in four replications: (1) Control (Hoagland’s solution minus N solution excluding Azolla; (2) Hoagland’s minus N solution including Azolla; (3) full Hoagland’s solution plus Azolla; and (4) full Hoagland’s solution excluding Azolla. Results show that photosynthetic rate, evapotranspiration, intercellular CO2 concentration and chlorophyll were generally higher in full Hoagland’s solution. This was closely followed by full Hoagland’s solution plus Azolla, and Hoagland’s minus N solution plus Azolla treatments. The lowest photosynthetic rates and chlorophyll contents were found in the control (Hoagland’s minus N solution) treatment.Keywords: Photosynthetic rate, stomatal conductance, evapotranspiration, intercellular CO2 concentration, chlorophyll a, chlorophyll bAfrican Journal of Biotechnology Vol. 12(16), pp. 2006-201

The possible effect of the bioaccumulation of disinfectant by-products on crops irrigated with treated wastewater

The shortage of potable water for irrigation of food crops in semi-arid developing countries led to the use of alternative sources of water. Wastewater is gaining importance for productive use in agriculturethroughout the world. A widely used and efficient method to reduce the occurrence of waterborne diseases in numerous wastewater plants is water chlorination. In early 1970s, some volatile halogenated organic compounds such as chloroform were identified in chlorinated surface waters containing high levels of natural organic material. Generally, the trihalomethanes (THMs), including chloroform, bromodicholoromethane, dibromochloromethane and bromoform were the most prevalent in chlorinated surface water. Predominant research studies focused on the carcinogenic and mutagenic properties of these compounds in treated wastewater. But little attention was paid to how these compounds in treatedwastewater could affect crop performance in agriculture, physiological changes amongst crop varieties and the build-up of these organic compounds in edible plant tissues with persistent use of treated waste-water. A probable reason for this was the absence of the practice of wastewater irrigation in food crop agriculture in the past. Current knowledge on the trihalomethanes and possible plant interactions with this group of volatile organic compounds are assessed in this review