Influence of pruning management on P and N distribution and use efficiency by N2 fixing and non-N2 fixing trees used in alley cropping systems

Pruning of hedgerow trees is an important management practice for the successful establishment of an alley cropping system. Although pruning affects biomass production, only meager evidence of this management on distribution of nutrients among the different plant organs after tree regrowth is available. This study examined the effect of pruning on the distribution and use efficiency of N and P in a N₂ fixing leguminous tree species, Gliricidia sepium, and two non-N₂ fixing leguminous tree species, Senna siamea and S. spectabilis, grown in a field on an Alfisol (low in P) at Fashola (Guinea Savanna Zone), Southwestern Nigeria. Four P rates, 0, 20, 40 and 80 kg P ha^–1 as single superphosphate were used and management treatments included pruned versus unpruned plants. The ¹⁵N isotope dilution technique was used to measure N₂ fixation in G. sepium. Partitioning of total P among different plant organs was influenced by plant species and pruning management, but was not affected by P application rates. The distribution of total P in the various plant organs followed that of dry matter yield while N partitioning had a different pattern. Pruned plants distributed about 118% more total P to branches and had a higher physiological P use efficiency (PPUE) than unpruned plants. Leaves were the biggest sink for total N and N allocation in the other plant organs was influenced by plant species and pruning management, G. sepium had relatively more of its total N and P partitioned into roots (about double that of the non-N₂ fixing trees) but had a lower PPUE. Unpruned and pruned G. sepium derived 35 and 54% respectively of their total N from atmospheric N2, with about 54% of the fixed N2 being allocated to leaves and roots. Results showed that N and P pools turned over in the branches during plant regrowth after pruning but the causative factors associated with this phenomenon were not clear.     

Polysaccharides from the seeds of Senna multijuga

The seeds of Senna multijuga were extracted with water or 1% acetic acid and treated with ethanol, resulting in two insoluble fractions. After purification, the major one (FIA, 23%) was shown to be a galactomannan (Man:Gal 2.3:1;[] = + 54.6;[η]=1340mlg⁻¹). It consists of a main chain of (1 → 4)-linked β-d-mannopyranosyl residues substituted at 06 by single-unit -d-galactopyranosyl side chains. The second fraction (FIB, 2.5%) was an O-acetyl-glucuronoarabinoxylan from the seed coats (O-acetyl 8.3 mol%; glucuronic acid 11.7%, Xyl:Ara ratio 20:1), which showed a predominance of 4-O-substituted Xylp units (84.4%), branched at 03 with non-reducing end units of Xylp, Araf and glucuronic acid. The O-acetyl positions in d-xylosyl units are at 02 (4.8%), 03 (4.4%) and 02,3 (0.9%). The ratio between 03 and 02 determined by ¹³C-nuclear magnetic resonance spectroscopy is 1.5:1.     

A striking new unifoliolate and polycarpellate species of Senna (Fabaceae: Caesalpinioideae) from Andhra Pradesh,India

Senna andhrica P.V. Ramana, J. Swamy and M. Ahmedullah, a new species from Andhra Pradesh, India, is described. The species is remarkable in having unifoliolate, oblong or ovate leaves, 2–3 carpellate gynoecium and reniform seeds. It is the second described species with unifoliolate leaves in the Cassiinae. In most other morphological characters, it is closely allied to Senna occidentalis (L.) Link.     

Effect of row spacing on biological control of sicklepod (Senna obtusifolia) with Colletotrichum gloeosporioides

In field experiments conducted over 3 years, the mycoherbicidal fungus Colletotrichum gloeosporioides, formulated either in 20% (v/v) unrefined corn oil and 0.2% Silwet L-77 surfactant or with an invert emulsion, provided season-long control of Senna obtusifolia in narrow (51 cm) rows of soybean. However, in wide (102 cm) rows, one application of either formulation failed to provide season-long control of S. obtusifolia, and two applications were required to achieve season-long weed control. In narrow (51 cm) rows, one application of the fungus either in unrefined corn oil or an invert emulsion controlled S. obtusifolia an average of >90%, and a second application was not required for season long weed control. Soybean yields in wide-row plots treated with two applications of either the fungus/corn oil or fungus/invert emulsion, or with a single application of the fungal treatments in narrow-row soybean plots, were not significantly different from weed-free control plots, or from plots treated with the herbicide chlorimuron. These results suggest that row spacing can affect mycoherbicidal efficacy of this fungus for controlling S. obtusifolia.     

Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass

Complementarity in the distribution of tree and crop root systems is important to minimise competition for resources whilst maximising resource use in agroforestry systems. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare the distribution and dynamics of root length and biomass of a 3-year-old Grevillea robusta A. Cunn. ex R. Br. (grevillea) tree row and a 3-year-old Senna spectabilis DC. (senna) hedgerow grown with Zea mays L. (maize). Tree roots were sampled to a 300 cm depth and 525 cm distance from the tree rows, both before and after maize cropping. Maize roots were sampled at two distances from the tree rows (75–150 cm and 450–525 cm) to a maximum depth of 180 cm, at three developmental stages. The mean root length density (L_rv) of the trees in the upper 15 cm was 0.55 cm cm⁻³ for grevillea and 1.44 cm cm⁻³ for senna, at the start of the cropping season. The L_rv of senna decreased at every depth during the cropping season, whereas the L_rv of grevillea only decreased in the crop rooting zone. The fine root length of the trees decreased by about 35% for grevillea and 65% for senna, because of maize competition, manual weeding, seasonal senescence or pruning regime (senna). At anthesis, the L_rv of maize in the upper 15 cm was between 0.8 and 1.5 cm cm⁻³. Maize root length decreased with greater proximity to the tree rows, potentially reducing its ability to compete for soil resources. However, the specific root length (m g⁻¹) of maize was about twice that of the trees, so may have had a competitive uptake advantage even when tree root length was greater. Differences in maize fine root length and biomass suggest that competition for soil resources and hence fine root length may have been more important for maize grown with senna than grevillea. This revised version was published online in June 2006 with corrections to the Cover Date.     

Adjuvants enhance the biological control potential of an isolate of Colletotrichum gloeosporioides for biological control of sicklepod (Senna obtusifolia)

In greenhouse experiments, unrefined corn oil, Silwet L-77, and an invert emulsion were tested as adjuvants with the mycoherbicidal fungus Colletotrichum gloeosporioides, a weakly virulent pathogen of sicklepod (Senna obtusifolia). A 1:1 (v/v) fungus/corn oil tank mixture containing 0.2% (v/v) Silwet L-77 surfactant reduced the dew period requirements for maximum weed infection and mortality from 16 to 8 h, and delayed the need for free moisture for greater than 48 h. This formulation also resulted in the ability of the pathogen to infect and kill weeds in larger (>5 leaf) growth stages. The invert emulsion resulted in similar effects upon these parameters. These results suggest that invert emulsions, unrefined corn oil and Silwet L-77 surfactant greatly improve the bioherbicidal potential of this pathogen for control of sicklepod, a serious weed pest in the southeastern US.     

Effect of liana cutting on water potential and growth of adult<Emphasis Type="Italic"> Senna multijuga</Emphasis> (Caesalpinioideae) trees in a Bolivian tropical forest

Lianas, or woody climbing plants, are a major constituent of seasonally dry tropical forests, and are thought to impact negatively their host trees. In this study we evaluated whether liana presence was associated with reduced leaf water potentials and growth in adult Senna multijuga trees during the dry season in a lowland Bolivian forest. We used leaf water potentials in trees as a first approach to assess trees’ water status, under the assumption that leaf water potentials become more negative when water losses (via transpiration) exceed gains (by uptake). We measured relative growth in girth at 1.5 m height (gbh) to quantify tree growth. At the beginning of the 1996 dry season (early June), we selected 20 S. multijuga trees 10–20 cm dbh, and measured their gbh. We also recorded pre-dawn and mid-day leaf water potentials in these trees. In ten experimental trees all lianas were then cut, while the remaining trees were used as controls. Pre-dawn and mid-day water potentials were re-measured 1 day after liana-cutting, and then every week in all trees for 1 month and then at 3 and 5 months, until the beginning of the next rainy season (November); gbh was measured again in July 1997 to estimate relative growth rate. Liana removal was associated with less negative pre-dawn (–0.3 vs –0.4 MPa) and mid-day (–0.5 vs –0.7 MPa) water potentials in trees during the dry season. This difference appeared as early as 1 day after cutting, and disappeared once the rainy season began. Liana-cut trees grew more (0.4 mm/mm year) than liana-uncut trees (0.2 mm/mm year). These findings suggest that lianas may interfere with water availability to these trees during the dry season, and may also hinder tree growth. Received: 16 November 1999 / Accepted: 23 March 2000     

Leishmanicidal activity of the crude extract,fractions and major piperidine alkaloids from the flowers of Senna spectabilis

Senna spectabilis (sin. Cassia excelsa, C. spectabilis) is an endemic tree of South America and Africa, very common in Brazil, where it is known as “canafistula-de-besouro” and “cassia-do-nordeste”. In folk medicine, this plant is indicated for the treatment of constipation, insomnia, anxiety, epilepsy, malaria, dysentery and headache. Phytopharmacological studies have also confirmed anticonvulsive, sedative, anti-malarial, antimicrobial and cytotoxic properties of many parts of S. spectabilis. In this communication, we present a comparative study of the leishmanicidal activity of the crude ethanolic extract, its fractions and also the two major alkaloidal metabolites (−)-cassine/(−)-spectaline, trying to establish a relationship between the presence of piperidine alkaloidal constituents and leishmanicidal activity. The growth inhibitory effect of promastigote forms of Leishmania major was determined for the crude extract, fractions of the flowers of S. spectabilis and a mixture of (−)-cassine/(−)-spectaline in comparison to pentamidine used as standard drug. The cytotoxic effects were assessed on macrophage strain J774 by lactate dehydrogenase assay. Fractions dichloromethane (FL-DCM) and n-butanol (FL-Bu) and a mixture of (−)-cassine/(−)-spectaline (∼7:3) exhibited significant activity against the parasite Leishmania major (IC₅₀ values of 0.6 ± 0.1 μg/ml, 1.6 ± 0.9 μg/ml and 24.9 ± 1.4 μg/ml, respectively), without toxic effects on murine macrophages. Due to the promising results elicited, further studies in vivo need to be performed to confirm the therapeutic potential of Senna spectabilis.     

Biosynthesis of gold and silver nanoparticles using Senna alexandrina Miller extract against Culex pipiens L. (Diptera: Culicidae)

The use of nanoparticles for various purposes, including pest control, has become increasingly popular because of their cost and environmental safety. In the present study, gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) were synthesized in an extract of Senna alexandrina Miller leaves with the aim of use against vectors of disease such as Culex pipiens L. (the filarial vector in Saudi Arabia). The nanoparticles were characterized by scanning electron microscopy and spectroscopic techniques. The larvicidal activity of the nanoparticles against Cx. pipiens was evaluated according to the protocol of the World Health Organization. According to the lethal concentration LC₅₀, the result shows differentiation in the sensitivity on mosquitoes. The AuNPs (51.383 ppm) the best one followed by AgNPs (52.525 ppm) while S. alexandrina leaf extract alone (355.25 ppm), the lowest effectiveness. Generally, the Cx. pipiens mosquito larvae proved to be more susceptible to AuNPs and AgNPs than leaf extract alone by about 6.91 and 6.76 times, respectively.