Taxonomy, phylogeny and population biology of the red band needle blight pathogen and related species

Chapter one of this thesis presents the literature pertaining to biological invasions and the different stages of invasions in terms of plant pathogens. The review focuses on determining areas where studying the population genetics of a pathogen might complement the knowledge of the ecology of the pathogen in order to gain a better understanding of their evolutionary and invasive potential. Dothistroma septosporum, which causes Dothistroma needle blight (DNB), is one of the better known examples of an invasive plant pathogen and is the focus of this thesis. After presenting an overview of the pathogen, it is concluded that a thorough knowledge of the ecological aspects of the pathogen has been gained by many intensive studies but that there is a distinct, and perhaps dangerous, lack of knowledge pertaining to the global population genetics of this pathogen. Throughout the years of this study, DNB has become a global concern as more epidemics were being reported, not only in the Southern Hemisphere where the disease has been problematic for over 50 years, but also in the Northern Hemisphere in both native and nonnative forests. An “International Dothistroma Alliance Committee” was established in 2004 among researchers world-wide with the aim being to share and integrate knowledge about the pathogen and the disease it causes. The main focus of this group incorporates aspects such as diagnostics and monitoring, assessing pathogen risk (pest-risk), disease impact, management and pathogen variability as well as population diversity. The research in this thesis greatly assists in the latter two aims of the committee. In the second chapter, multigene phylogenies were constructed from Dothistroma septosporum isolates obtained worldwide. These studies revealed that the disease is not caused by one pathogen with varying morphotypes, but that two, very closely related sibling species are responsible. A thorough description of the two species, named Dothistroma septosporum and D. pini, is provided. It is also shown in Chapter six that both species are capable of infecting the same needle and can co-exist within the same conidioma. There is thus a distinct potential for hybridisation to occur between these two species. Coincident with the initiation of this research is an increase globally in the incidence of DNB. This increased the knowledge base about the pathogens around the world and also made it easier to obtain cultures and isolates for this study from different sources. As a consequence, an understanding of the distribution and occurrence of each species was possible and is documented in Chapters three and six. The molecular techniques developed in this work have enabled the development of a robust technique to distinguish between the two pathogens causing DNB. A combination of the species-specific mating type markers designed by Groenewald et al. (2007), the diagnostic Primer_A, and an effective species-specific RFLP test, provide a quick and effective means of identifying the DNB pathogens, directly or indirectly, from conidiomata on infected needles. In order to study the population diversity of the DNB fungi, twelve microsatellite markers were developed in Chapter three. In Chapter four, the preliminary applications of these markers provide a first glimpse of the global diversity of D. septosporum which has caused the most devastation world-wide. From this research it is also obvious that the pattern of diversity reflects the movement of its host (pine) from its native Northern Hemisphere to various countries within the Southern Hemisphere. Dothistroma septosporum is an important disease of both plantation grown pines and native forests. Climate change and the continual movement of infected plant material pose great threats to existing forests. The fact that a sibling species has been discovered shows the evolutionary potential of the species to adapt to changing environments. Successful quarantine and monitoring will aid in curbing the further spread of the disease into areas where it could, potentially, be more devastating. The chapters in this thesis correspond to different research projects and are represented in the text in the format of a publication. Due to the nature of this style, however, there is some unavoidable repetition in the text, especially within the introduction of each chapter. Three of the chapters within this thesis have been published in internationally recognised ISI rated journals.Thesis (PhD)--University of Pretoria, 2009.GeneticsUnrestricte

Promoting social inclusion? The impact of village services on the lives of older people living in rural England

Drawing on data from a qualitative study, this paper explores the impact of ‘village services’ on the lives of people aged 70 or more years living in rural England. Throughout the paper, the phrase ‘village services’ refers to six community-based services and activities provided to help meet the needs of older rural residents, namely lunch clubs, welfare rights information and advice services, befriending schemes and community warden support, in rural areas in three regions of England. It is argued that, in various ways, village services promote social inclusion by enhancing older rural residents' access to the resources, rights, goods and services that encourage social interaction and meaningful participation in community life. It is clear, however, that the overwhelming majority of users of village services are female, that older men are often reluctant to engage with the services on offer, and that the providers of village services need to find new and innovative ways of engaging with older men in rural areas. It is concluded that restricted revenue and capital resources means that the expansion of village services so that they may better meet the requirements of older rural men is unlikely

Qualitative assessment of links between exposure to noise and air pollution and socioeconomic status

The scope of the work requested under this specific contract is to provide a report/assessment text that may be directly incorporated into EEA’s 2018 report exploring the linkages between socioeconomic status (SES) in Europe and exposure to air and noise pollution, as well as to climate-related impacts. More specifically, this report builds on the findings of the 2016 Science for Environment Policy (SEP) report to provide an updated qualitative review of the latest evidence and state of knowledge regarding the role of SES in determining exposure, susceptibility and vulnerability to air pollution and noise, documenting research that explores the multiple factors and drivers that can lie behind these linkages. This review has identified and synthesised evidence from a wide range of sources in response to the objectives set by the EEA and covers evidence relating to at least 18 of the EEA-33 countries. The conclusions presented here explicitly identify where this review confirms, contradicts or adds to the conclusions of the SEP report

Calonectria in the age of genes and genomes : towards understanding an important but relatively unknown group of pathogens

The genus Calonectria includes many aggressive plant pathogens causing diseases on various agricultural crops as well as forestry and ornamental tree species. Some species have been accidentally introduced into new environments via international trade of putatively asymptomatic plant germplasm or contaminated soil, resulting in significant economic losses. This review provides an overview of the taxonomy, population biology, and pathology of Calonectria species, specifically emerging from contemporary studies that have relied on DNA-based technologies. The growing importance of genomics in future research is highlighted. A life cycle is proposed for Calonectria species, aimed at improving our ability to manage diseases caused by these pathogens.The National Key R&D Program of China (China-South Africa Forestry Joint Research Centre Project); the National Ten-thousand Talents Program; the GuangDong Top Young Talents Program.http://wileyonlinelibrary.com/journal/mpphj2023BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

A Search for In-Situ Field OB Star Formation in the Small Magellanic Cloud

Whether any OB stars form in isolation is a question central to theories of massive star formation. To address this, we search for tiny, sparse clusters around 210 field OB stars from the Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC (RIOTS4), using friends-of-friends (FOF) and nearest neighbors (NN) algorithms. We also stack the target fields to evaluate the presence of an aggregate density enhancement. Using several statistical tests, we compare these observations with three random-field datasets, and we also compare the known runaways to non-runaways. We find that the local environments of non-runaways show higher aggregate central densities than for runaways, implying the presence of some "tips-of-iceberg" (TIB) clusters. We find that the frequency of these tiny clusters is low, $\sim 4-5\%$ of our sample. This fraction is much lower than some previous estimates, but is consistent with field OB stars being almost entirely runaway and walkaway stars. The lack of TIB clusters implies that such objects either evaporate on short timescales, or do not form, implying a higher cluster lower-mass limit and consistent with a relationship between maximum stellar mass ($m_{\rm max}$) and the mass of the cluster ($M_{\rm cl}$). On the other hand, we also cannot rule out that some OB stars may form in highly isolated conditions. Our results set strong constraints on the formation of massive stars in relative isolation.Comment: 24 pages, 13 figures, Accepted to Ap

Dothistroma septosporum identified in Greece on Pinus brutia and Pinus nigra plantations

No abstract available.http://apsjournals.apsnet.org/loi/pdishb201

Microsatellite and mating type primers for the maize and sorghum pathogen, Exserohilum turcicum

Northern corn leaf blight (NCLB) is a destructive foliar disease of maize that results from infection with the fungal pathogen, Exserohilum turcicum. Annual yield losses incurred from NCLB in South Africa may exceed 50 % when environmental conditions optimal for disease development prevail. In order to study the genetic diversity of E. turcicum, 13 microsatellite markers and mating type PCR primers were developed. Thirty-two primer pairs were designed from the E. turcicum genome sequence to flank microsatellite regions. A multiplex PCR assay amplifying both mating type idiomorphs was designed from the MAT1-1 and MAT1-2 gene sequences, and a protocol for multiplex PCR amplification of MAT loci was optimized. Initial screening identified 13 microsatellite regions that were polymorphic in 9 isolates of E. turcicum. To test the efficacy of the markers, 26 isolates of E. turcicum from 6 South African provinces, including 2 isolates from sorghum, were genotyped. A total of 90 alleles across 13 loci were obtained and the gene diversity ranged from 0.074 to 0.929. Cross-species amplification withE. rostratum was obtained for one SSR marker (SSR27). The MAT markers were specific to E. turcicum and could be used to differentiate isolates of E. turcicum and E. rostratum. The markers developed in this study will be useful to elucidate the population genetic structure, genetic diversity and mode of reproduction of E. turcicum on maize and sorghum.Research supported in part by the National Research Foundation of South Africa (grant specific unique reference number (UID) 85076), and by the Maize Trust and the University of Pretoria’s Research and Development Programme.http://link.springer.com/journal/133132015-09-30hb201