Comparison of<i>Thinopyrum intermedium</i>derivatives carrying barley yellow dwarf virus resistance in wheat

Resistance to both barley yellow dwarf virus (BYDV) and cereal yellow dwarf virus (CYDV) has been demonstrated in wheat genetic stocks with Thinopyrum intermedium chromatin. A number of resistance-bearing translocations have been reported on chromosome arm 7DL from two independent Th. intermedium sources; one source is the addition line L1 and the other is the spontaneous substitution line P29. Another source of resistance in wheat cytogenetic stocks is available as a 2Ai(2D) substitution line. We used a set of 38 molecular markers and the available deletion stocks to compare the size of the 7DL translocations more comprehensively than has been done previously. We also compared the efficacy of BYDV resistance of the various genetic stocks both before and after transfer to a common genetic background. TC14 was confirmed as carrying the smallest translocation, replacing about 20% of the distal end of 7DL. TC5 and TC10 had 90% of the chromosome arm replaced by Th. intermedium chromatin; the proximal 10% corresponded to wheat chromatin. YW642 appeared to have the whole 7DL replaced by Th. intermedium chromatin, as confirmed by the co-dominant marker cfd68 mapping on the bin nearest the centromere. Translocation line P961341 had bins 3, 7, and 8 replaced by Th. intermedium chromatin, making this the second smallest translocation with BYDV and CYDV resistance. The translocation sizes reported here differ from some of the previous estimates. The translocated Th. intermedium segments appeared to be bigger than the replaced wheat 7DL fragments. All the resistances derived from the L1 and P29 group 7 chromosomes and the 2Ai#2 chromosome were effective in reducing the number of infected plants and the mean virus titre, regardless of the background. Some evidence is discussed suggesting the long arm of the Th. intermedium group 7 chromosome 7Ai#1 carries two resistances, the distal Bdv2 and a proximal second gene.</jats:p

Local Perception of Risk to Livelihoods in the Semi-Arid Landscape of Southern Africa

The United Nations and Intergovernmental Panel on Climate Change deem many regions of southern Africa as vulnerable landscapes due to changing climatic regimes, ecological conditions, and low adaptive capacity. Typically in highly vulnerable regions, multiple livelihood strategies are employed to enable sustainable development. In Botswana, livelihood strategies have diversified over time to include tourism and other non-agricultural activities. While such diversification and development have been studied, little is known about how locals perceive livelihood risks. This article analyzes perceptions of risk through a risk hazards framework. During the summer of 2010, 330 surveys were completed within seven villages in northern Botswana and the Caprivi Strip of Namibia. During the survey respondents were asked to list the biggest threats/challenges to their livelihoods. Responses were grouped into categories of risk according to the capital assets on which livelihoods depend: natural, physical, financial, human, and social. A risk mapping procedure was utilized, for which indices of severity, incidence, and risk were calculated. It is hypothesized that people’s perception of risk is directly dependent on environmental conditions and employment status of the household. Results indicate that problems related to natural and financial assets are the greatest source of risk to livelihoods. Furthermore, flood, drought, and other measures of climate variability are perceived as influential, typically negatively, to livelihood strategies