Associations between grain yield and carbon isotope discrimination in cowpea

Twenty cowpea (Vigna unguiculata L. Walp.) genotypes, comprising Kenyan cultivars and Kenyan and introduced breedings lines, were grown in 15 replicated field trials carried out at three locations in semi-arid eastern Kenya over four seasons. Grain and straw yields and the carbon isotope discrimination (Δ) of this material were determined, and days to flowering and maturity observed.None of the seasons in which the trials were conducted was appreciably drier than the long term average for the sites, and some trials received excessive rain. Averaging the data for the 15 trials, one genotype yielded much less grain (77 g m⁻²) than the 19 others, whose yield ranged from 125 to 177 g m⁻² (average 148 g m⁻²). Trial mean yield trials had a high straw Δ (r = +0.567) and had received more rain between flowering and maturity (r = +0.428) than lower yielding ones. Among genotypes, averaging over trials, the correlation coefficient (r) between grain yield and grain Δ was +0.394, and between grain yield and straw Δ, +0.460. Early genotypes had the highest grain Δ and straw Δ. The correlation among genotypes between date of flowering and grain Δ was −0.632 and with straw Δ, −0.502. When comparisons were made among trials, there was no clear relationship between the strength of the correlations among genotypes between grain yield and straw Δ or grain Δ and the degree of stress experienced by a trial (as indicated by the rainfall it had received). It appeared that this was because the variances of grain Δ and straw Δ were greater in the most droughted trials, whereas the variance of yield was greatest in the least droughted trials.It is concluded that the genetic correlation between grain yield and either grain Δ or straw Δ is unlikely to be strong enough to make either Δ a useful surrogate or adjunct in selecting for high yield in the segregating generations of a breeding programme for semi-arid eastern Kenya, but that Δ may be of value in the selection of parent genotypes.     

Threatened plants in Southern Africa

Computer-based aids have been used extensively to support surveys of threatened plants in Southern Africa. The surveys have shown that by far the highest concentration of threatened plants occurs in the relatively small area of the Cape Floristic Kingdom, a region with many local endemics that are easily put in hazard by impacts such as agriculture, invasive exotics and over-frequent fires. Of the estimated 20 000 vascular plants in Southern Africa, 2373 appear to be critically rare, threatened or recently extinct. Sixty-eight per cent of the plants in hazard occur in the Cape Floristic Kingdom. Obstacles to conservation, particularly a lack of nature reserves in critical areas, are discussed.     

Phocine distemper virus in the North and European Seas - Data and models, nature and nurture

Two outbreaks of phocine distemper have severely affected harbour seal (Phoca vitulina) populations in European and UK waters. The first occurred in 1988 when the causative virus was identified as a new member of the genus morbillivirus. The second outbreak in 2002 was first detected on the same Danish Island of Anholt and involved similar populations and geographical locations. However, despite the obvious similarities between the epidemics, differences in viral transmission and case mortality were found. Harbour seals are highly susceptible to infection while sympatric grey seals (Halichoerus grypus) are resistant but could be important asymptomatic carriers of the disease. Arctic phocid seals remain the most likely source of the virus and grey seals could be the link between these primary hosts and the harbour seal populations further south. Future epidemiological models should therefore consider including multiple host species. The future conservation and management of harbour seal populations vulnerable to PDV relies on the ability to accurately predict the long-term impact on population abundance and distribution. Although knowledge about the behaviour and pathogenesis of the virus has increased substantially and data on host movements and contact rates are accumulating, studies into the determinants of the host range have lagged behind. The development of more realistic epidemiological models should be combined with studies into the factors controlling species and individual susceptibility. Assessing the risk of infection to endangered but currently unexposed potential host species (such as the Hawaiian monk seal, Monachus schauinslandi) is essential for guiding potential conservation management options, such as vaccination     

Physiological and biochemical characterization of quinclorac resistance in a false cleavers (Galium spurium L.) biotype

The physiological and biochemical basis for quinclorac resistance in a false cleavers (Galium spurium L.) biotype was investigated. There was no difference between herbicide resistant (R) and susceptible (S) false cleavers biotypes in response to 2,4-D, clopyralid, glyphosate, glufosinate-ammonium, or bentazon. On the basis of GR(50) (growth reduction of 50%) or LD(50) (lethal dose to 50% of tested plants) values, the R biotype was highly resistant to the acetolactate synthase (ALS) inhibitor, thifensulfuron-methyl (GR(50) resistance ratio R/S = 57), and quinolinecarboxylic acids (quinclorac R/S = 46), resistant to MCPA (R/S = 12), and moderately resistant to the auxinic herbicides picloram (R/S = 3), dicamba (R/S = 3), fluroxypyr (R/S = 3), and triclopyr (R/S = 2). The mechanism of quinclorac resistance was not due to differences in [(14)C]quinclorac absorption, translocation, root exudation, or metabolism. Seventy-two hours after root application of quinclorac, ethylene increased ca. 3-fold in S but not R plants when compared to controls, while ABA increased ca. 14-fold in S as opposed to ca. 3-fold in R plants suggesting an alteration in the auxin signal transduction pathway, or altered target site causes resistance in false cleavers. The R false cleavers biotype may be an excellent model system to further examine the auxin signal transduction pathway and the mechanism of quinclorac and auxinic herbicide action.     

Recovery of saturated hydraulic conductivity under secondary succession on former pasture in the humid tropics

Landscapes in the humid tropics are undergoing a continuous change in land use. Deforestation is still taking its toll on forested areas, but at the same time more and more secondary forests emerge where formerly agricultural lands and pastures are being abandoned. Regarding soil hydrology, the extent to which secondary succession can recover soil hydrological properties disturbed by antecedent deforestation and pasture use is yet poorly understood. We investigated the effect of secondary succession on saturated hydraulic conductivity (Ks) at two soil depths (0-6 and 6-12 cm) using a space-for-time approach in a landscape mosaic in central Panama. The following four land-use classes were studied: pasture (P), secondary forest of 5-8 years of age (SF5), secondary forest of 12-15 years of age (SF12) and secondary forest of more than 100 years of age (SF100), each replicated altogether four times in different micro-catchments across the study region. The hydrological implications of differences in Ks in response to land-use change with land use, especially regarding overland flow generation, were assessed via comparisons with rainfall intensities.Recovery of Ks could be detected in the 0-6 cm depth after 12 years of secondary succession: P and SF5 held similar Ks values, but differed significantly (α = 0.05) from SF12 and SF100 which in turn were indistinguishable. Variability within the land cover classes was large but, due to sufficient replication in the study, Ks recovery could be detected nonetheless. Ks in the 6-12 cm depth did not show any differences between the land cover classes; only Ks of the uppermost soil layer was affected by land-use changes. Overland flow - as inferred from comparisons of Ks with rainfall intensities - is more likely on P and SF5 sites compared to SF12 and SF100 for the upper sample depth; however, generally low values at the 6-12 cm depth are likely to impede vertical percolation during high rainfall intensities regardless of land use.We conclude that Ks can recover from pasture use under secondary succession up to pre-pasture levels, but the process may take more than 8 years. In order to gain comprehensive understanding of Ks change with land use and its hydrological implications, more studies with detailed land-use histories and combined measurements of Ks, overland flow, precipitation and throughfall are essential.     

Tree plantations on farms: Evaluating growth and potential for success

Interest in native species is growing across the tropics as reforestation of degraded lands becomes more widespread. In this study four tree species native to Panama - Cedrela odorata, Pachira quinata, Samanea saman, and Tabebuia rosea - were grown on rural farms at two dry tropical sites in Panama for up to five years. Survivorship and growth data at these “on-farm” trials are compared to data recorded from nearby experimental or “species selection” trial sites and evaluated in terms of soil fertility and management. Participant farmers were also asked about their interest in planting trees in general as well as their interest in 61 species grown in the species selection trial.Although, on-farm survivorship was variable and generally lower than that found on the species selection trial, one species (S. saman) experienced high and consistent survivorship. High survivorship combined with growth data from farms at both sites for this species suggests it would be a good candidate for extension projects working with rural farmers. Survivorship of other species appears more sensitive to farmer management and/or local site conditions. Generally lower growth on the Los Santos farms as compared to the species-selection trial is attributed to the lower soil fertility (plant available P) at the on-farm sites compared to the species selection trial. In contrast, only one species - P. quinata - had a growth variable found to be significantly lower between the on-farm and species selection trial sites in Rio Hato. C. odorata, P. quinata T. rosea can all be used in on-farm conditions with consideration to specific site and management conditions.By 2009, approximately 80% of the farmers planting trees still wished to participate in tree planting activities. All of the farmers no longer wishing to continue with the project expressed slow growth rates of trees as a principal reason. All but one of these farmers had growth rates for his/her trees markedly below those of the species selection trial nearby. Some farmers wishing to continue had very high mortality rates (>70% for all species), suggesting non-tangible benefits for participating in project activities. Other species that were not tested on-farm but grew well in the species-selection trials and were of interest to local farmers are discussed.As long as specific site and management conditions are carefully considered, data from species selection trials can be useful in informing tree planting projects with rural farmers; however, care should be taken to manage expectations.     

The gas phase oxidation of elemental mercury by ozone

The gas phase reaction between elemental mercury (Hg⁰) and ozone (0₃) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 0₃ concentrations above 20 ppm, a loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3±2×10^?20 cm³ molec.^?1 s^?1 at 20 °C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 0₃ concentration of 30 ppb.     

Immunoaffinity purification of chlorimuron-ethyl from soil extracts prior to quantitation by enzyme-linked immunosorbent assay

A competitive-indirect enzyme-linked immunosorbent assay (CI-ELISA) was developed to quantify chlorimuron-ethyl in soil. The linear working range of the assay was from 1 to 1000 ng mL(-)(1). The assay had an I(50) value of 54 ng mL(-)(1), with a limit of detection of 2 ng mL(-)(1) and a limit of quantification of 27 ng mL(-)(1). Three soils were extracted using a carbonate buffer (pH 9.0) and the extracts spiked with chlorimuron-ethyl. Because of the effects of coextractants (matrix effects) from soil on the accuracy and precision of the ELISA, immunoaffinity chromatography (IAC) was used to purify chlorimuron-ethyl from soil extracts prior to analysis. The immunoaffinity columns, which had a total binding capacity of 1350 ng of chlorimuron-ethyl mL(-)(1) of immunosorbent, were prepared by binding anti-chlorimuron-ethyl antibodies to protein G Sepharose 4B. Although the matrix effects were largely removed using the affinity column, they could be completely removed by first passing the extract through a column containing epoxy-coupled 1,6-diaminohexane (EAH) Sepharose 4B to remove organic acids prior to IAC. Assay sensitivity was increased 100-fold using IAC to purify and simultaneously concentrate chlorimuron-ethyl from soil extracts. The purification strategy (EAH followed by IAC chromatography) removed matrix effects from all three soils and allowed for the accurate quantitation of chlorimuron-ethyl in soil extracts.     

Amelioration of a hardsetting Alfisol through deep mouldboard ploughing, gypsum application and double cropping. III. Crop production and profitability

Deep mouldoard ploughing to 0.45 m, gypsum application (5 t ha⁻¹), and double cropping were evaluated, alone and combined, as ameliorants for a hardsetting red-brown earth (Alfisol). The double cropped treatment consisted of winter wheat (Triticum aestivum) and a summer forage crop consisting of sudax (Sorghum sudanese) intersown with cowpea (Vigna unguiculata). This paper describes the effect of these treatments on crop development, yield, crop-water relations and economic returns. Crop emergence was not affected by any treatment. Mouldboard ploughing significantly increased wheat grain yield from 1.86 to 2.15 t ha⁻¹, in 1984, but not in 1985. Yield was also increased from 5.18 to 5.68 t ha⁻¹ as a result of gypsum addition in 1985—after no significant difference in 1984. Double cropping significantly increased yield (by 0.6 t ha⁻¹) in 1985. Greater increases were obtained with the summer cropping phase where higher evaporative demand during the summer would have aggravated soil structural problems associated with hardsetting. Sudax-cowpea dry matter yields were increased from 13.6 to 17 t ha⁻¹ and from 13.0 to 17.5 t ha⁻¹ during summer 1984–1985 by gypsum and mouldboard ploughing, respectively. The higher yields are attributed to increased water storage and depletion, and reduced soil strength for the mouldboard ploughed and gypsum main treatments. No interactions were found between the main treatments, except at the end of the 1985 winter cropping phase when there was a negative interaction between mouldboard ploughing and gypsum application for dry matter, equivalent root length and yield. The yield increases associated with mouldboard ploughing did not persist beyond the second year of the experiment. Double cropping combined with mouldboard ploughing (Mb+DC) was the most profitable treatment, whereas mouldboard ploughing with gypsum (Mb+G) was the least profitable for the crops grown in this experiment.     

Autophagy genes are essential for dauer development and life-span extension in C. elegans

Both dauer formation (a stage of developmental arrest) and adult life-span in Caenorhabditis elegans are negatively regulated by insulin-like signaling, but little is known about cellular pathways that mediate these processes. Autophagy, through the sequestration and delivery of cargo to the lysosomes, is the major route for degrading long-lived proteins and cytoplasmic organelles in eukaryotic cells. Using nematodes with a loss-of-function mutation in the insulin-like signaling pathway, we show that bec-1, the C. elegans ortholog of the yeast and mammalian autophagy gene APG6/VPS30/beclin1, is essential for normal dauer morphogenesis and life-span extension. Dauer formation is associated with increased autophagy and also requires C. elegans orthologs of the yeast autophagy genes APG1, APG7, APG8, and AUT10. Thus, autophagy is a cellular pathway essential for dauer development and life-span extension in C. elegans.