Arbuscular mycorrhizal fungi in organic systems

Arbuscular mycorrhizal fungi (AMF) are potential contributors to plant nutrition and pathogen suppression in low input agricultural systems, although individual species of AMF vary widely in their functional attributes. Recent studies at HRI and elsewhere have suggested that in some agricultural systems inoculum of AMF is substantially lower under conventional management relative to that under organic management. Further studies have suggested that conventional management selects AMF communities with limited benefits to their plant hosts relative to those in organic systems. There is a need to investigate the generality of these findings, and their implications for the productivity of organic systems, particularly during the period following conversion to organic management. The current project was designed to pull together existing understanding of the role, and potential role, of AMF in organic systems, and to identify sites and develop methods for use in a subsequent research programme. The project had three objectives: 01 To deliver a literature review covering current knowledge of the role of AMF in conventional and organic agricultural systems. The review considered the ways in which management influences the structure and functioning of AMF communities, including their contributions under conventional and organic management, and recommendations for future research needs. 02 To establish the extent of differences in AMF inoculum between organic and conventional systems, covering a range of management practices. Paired organic and conventional fields at 12 sites from across England were selected to investigate the relationships between management, AMF communities and soil chemistry. Organic and conventionally managed soils showed no significant difference in soil chemical properties (Organic C, total N, total P, extractable P, K, Mg). However, organically managed soils had greater AMF spore numbers and root colonisation potential, and therefore higher AMF inoculum potential, than conventionally managed soil. The relative difference in AMF spore numbers between organic and conventionally managed fields increased with time since conversion. Differences in AMF inoculum potential between organic and conventionally managed fields, and between farm sites, could not be related to differences in soil chemistry. 03 To develop a method suitable for characterising AM fungus communities in soil libraries, based on 18S rRNA terminal restriction fragment length polymorphism (T-RFLP) T-RFLP was shown to provide a rapid semi-quantitative method for analysis of AMF community diversity. However it was clear that primers currently used to amplify AMF are selective and do not allow diversity of the whole AMF community to be determined. Additionally these primers amplify contaminant fungi which need to be removed from the T-RFLP profile prior to analysis. However, contaminant diversity was shown to be low. The project has identified sites and techniques which could be valuable in future research to study the role of AMF under organic management. The study has also highlighted a number of key areas in which further research is needed in order to harness AMF to improve sustainability and productivity of organic and other agricultural systems. In particular, there is a need to determine the extent to which AMF diversity varies between organic and conventional management, the rate and mechanisms by which AMF diversity increases following conversion to organic production, the relationships between AMF diversity and crop nutrition/ pathogen control, and the soil factors controlling the effectiveness of AMF inoculum

Indigenous Research: Whose Priority? Journeys and Possibilities of Cross-Cultural Research in Geography

Decolonising research in geography is part of a broader ‘reflexive’ process which continues to question the positivist status of ‘researcher as observer’. This paper contributes to this reflexive turn, drawing on the particular experiences of a cross- cultural Honours thesis. The paper is pursued through a parallel journey involving a non-Indigenous researcher (and author of the cross-cultural Honours thesis) engaging Indigenous research1 with interpretative insight from an Indigenous adviser or ‘on-looker’. The methodological difficulties revealed by the parallel journey are emphasised to highlight both the complexities and reflexive possi- bilities of cross-cultural research but also to consider potential institutional and pedagogic implications that stem from the experience. One of the substantial findings of the paper is that, by linking Indigenous community priorities to research and coursework, conventional (and often unequal) research relations are minimised and colonising tendencies reduced. By challenging the conventional way that cross-cultural research is conceived, and the way that institutional practices and research frameworks are implemented, geographers can continue their prolonged and complex efforts at decolonisation of the field and their own practices

C32, A Young Star Cluster in IC 1613

The Local Group irregular galaxy IC 1613 has remained an enigma for many years because of its apparent lack of star clusters. We report the successful search for clusters among several of the candidate objects identified many years ago on photographic plates. We have used a single HST WFPC2 pointing and a series of images obtained with the WIYN telescope under exceptional seeing conditions, examining a total of 23 of the previously published candidates. All but six of these objects were found to be either asterisms or background galaxies. Five of the six remaining candidates possibly are small, sparse clusters and the sixth, C32, is an obvious cluster. It is a compact, young object, with an age of less than 10 million years and a total absolute magnitude of M_V = -5.78+/-0.16 within a radius of 13 pc.Comment: 5 pages, 5 figures, to be published in the May 2000 issue of the PAS

HII regions in dwarf irregular galaxies of the local group

Deep, narrowband H alpha Charge Coupled Device (CCD) surveys of HII regions were carried out in several dwarf irregular galaxies in and near the local group. Data are now complete for these galaxies: NGC 6822, GR 8, IC 10, IC 1613, Sextans A, Sextans B, and Sag Irr. Observations are complete for DDO 47, 53, 167, 168 and 187. Details of some of the results for the surveys completed so far are discussed. For NGC 6822, CCD survey at H alpha resulted in the detection of 145 HII regions in the local group irregular galaxy NGC 6822. Most of them are newly detected, faint surface-brightness objects. Positions, maps and dimensions are being published elsewhere. For GR 8, a deep narrowband H alpha imaging of the nearby dwarf irregular galaxy GR 8 revealed a total of 32 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies, except for size of sample effects. Most HII regions detected are at the very low luminosity end of the general luminosity function. For IC 10, a deep CCD narrowband H alpha imaging of the local group dwarf irregular galaxy IC 10 revealed a total of 144 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies

The Encapsidation of Herpes Simplex Virus Type 1 DNA

The herpes simplex virus genome contains an approximately 400 bp direct repeat at its ends known as the 'a' sequence, which contains all of the signals necessary for the cleavage and packaging of concatemeric replication products. During replication the genome is circularised, probably by direct ligation of the termini, generating a novel junction between two tandemly repeated 'a' sequences. We have cloned such a novel junction and in agreement with previous results (Nasseri & Mocarski, 1988), have shown that it can serve as a substrate for cleavage and packaging. The novel junction contains two highly conserved regions of the 'a' sequence which have been shown to be essential components of the packaging signal (pad and pac2). This thesis describes the introduction of specific mutations in this region and the development of a transient packaging assay to examine the effect of these mutations. In addition the mutants were tested for their ability to be serially propagated, extending the analysis beyond cleavage and packaging. Mutations were made using the motifs previously described by Deiss et al (1986). The pad and pac2 regions as a whole were deleted using convenient restriction enzyme sites and individual motif mutations, were introduced using a site directed mutagenesis method based on that described by Kunkel et al. (1991). The mutant sequences were then tested for their ability to direct cleavage and packaging in the transient packaging assay. This identified that both the pad and pac2 sequences as a whole represent essential components of the packaging signal. Both the location and the sequence of the pac2 T rich element were also shown to be essential in a functional cleavage and packaging signal. In addition a substitution mutation of the pac2 unconserved region reduced the efficiency of packaging directed by wt HSV-1 strain 17 but no effect on packaging efficiency was observed when HSV-2 strain HG52 was used. This result appears to indicate an unexpected divergence between HSV-1 and HSV-2. No function was attributable to either the conserved pac2 consensus sequence or any of the individual motifs of the pad sequence. However, considering the importance of the pad region as a whole the lack of identifiably important motifs is likely to reflect a level of redundancy within the pad region as opposed to a lack of biological function. Finally the mutants were used to examine the signals necessary for the serial propagation of defective genomes. This revealed that both GC rich regions of pad are involved in the serial propagation of defective genomes. No sequences within pac2 were identified as important. However, this may reflect either redundancy within the region or the importance of sequences which are also involved in DNA packaging

Identification and Analysis of Young Star Cluster Candidates in M31

We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ~60 arcmin^2, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (~<5 pc) young (~10-200 Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximations of their reddenings and ages. We also look for patterns of cluster formation with galactocentric distance, but our rough estimates are not precise enough to reveal any clear patterns.Comment: 32 pages, 9 figures, 5 tables, accepted to Ap