The draft genome sequence of Xanthomonas species strain Nyagatare, isolated from diseased bean in Rwanda.

types: Journal ArticleThis is a pre-copyedited, author-produced PDF of an article accepted for publication in FEMS following peer review. The version of record Aritua, V., Musoni, A., Kabeja, A., Butare, L., Mukamuhirwa, F., Gahakwa, D., . . . Smith, J. (2015). The draft genome sequence of Xanthomonas species strain Nyagatare, isolated from diseased bean in Rwanda, FEMS Microbiology Letters, 2015, Vol. 362, No. 4 pp. 1-4 is available online at: http://femsle.oxfordjournals.org/content/362/4/1.1.exploreWe announce the genome sequence for Xanthomonas species strain Nyagatare, isolated from beans showing unusual disease symptoms in Rwanda. This strain represents the first sequenced genome belonging to an as-yet undescribed Xanthomonas species known as species-level clade 1. It has at least 100 kb of genomic sequence that shows little or no sequence similarity to other xanthomonads, including a unique lipopolysaccharide synthesis gene cluster. At least one genomic region appears to have been acquired from relatives of Agrobacterium or Rhizobium species. The genome encodes homologues of only three known type-three secretion system effectors: AvrBs2, XopF1 and AvrXv4. Availability of the genome sequence will facilitate development of molecular tools for detection and diagnostics for this newly discovered pathogen of beans and facilitate epidemiological investigations of a potential causal link between this pathogen and the disease outbreak.Canadian International Development AgencyBBSRC SCPRI

Identification of Colletotrichum species associated with anthracnose disease of coffee in Vietnam

Colletotrichum gloeosporioides, C. acutatum, C. capsici and C. boninense associated with anthracnose disease on coffee (Coffea spp.) in Vietnam were identified based on morphology and DNA analysis. Phylogenetic analysis of DNA sequences from the internal transcribed spacer region of nuclear rDNA and a portion of mitochondrial small subunit rRNA were concordant and allowed good separation of the taxa. We found several Colletotrichum isolates of unknown species and their taxonomic position remains unresolved. The majority of Vietnamese isolates belonged to C. gloeosporioides and they grouped together with the coffee berry disease (CBD) fungus, C. kahawae. However, C. kahawae could be distinguished from the Vietnamese C. gloeosporioides isolates based on ammonium tartrate utilization, growth rate and pathogenictity. C. gloeosporioides isolates were more pathogenic on detached green berries than isolates of the other species, i.e. C. acutatum, C capsici and C. boninense. Some of the C. gloeosporioides isolates produced slightly sunken lesion on green berries resembling CBD symptoms but it did not destroy the bean. We did not find any evidence of the presence of C. kahawae in Vietnam

Genetic basis of control of Rhynchosporium secalis infection and symptom expression in barley

The genetic basis of several different components of resistance to Rhynchosporium secalis in barley was investigated in a mapping population derived from a cross between winter and spring barley types. Both the severity of visual disease symptoms and amount of R. secalis DNA in leaf tissues were assessed in field trials in Scotland in the 2007/2008 and 2008/2009 growing seasons. Relative expression of symptoms was defined as the residual values from a linear regression of amount of R. secalis DNA against visual plot disease score at GS 50. Amount of R. secalis DNA and visual disease score were highly correlated traits and identified nearly identical QTL. The genetic control of relative expression of symptoms was less clear. However, a QTL on chromosome 7H was identified as having a significant effect on the expression of visual disease symptoms relative to overall amount of R. secalis colonisationPeer reviewedFinal Accepted Versio

Periodic Host Absence Can Select for Higher or Lower Parasite Transmission Rates

This paper explores the effect of discontinuous periodic host absence on the evolution of pathogen transmission rates by using Ro maximisation techniques. The physiological consequence of an increased transmission rate can be either an increased virulence, i.e. there is a transmission-virulence trade-off or ii) a reduced between season survival, i.e. there is a transmission-survival trade-off. The results reveal that the type of trade-off determines the direction of selection, with relatively longer periods of host absence selecting for higher transmission rates in the presence of a trade-off between transmission and virulence but lower transmission rates in the presence of a trade-of between transmission and between season survival. The fact that for the transmission-virulence trade-off both trade-off parameters operate during host presence whereas for the transmission-survival trade-off one operates during host presence (transmission) and the other (survival) during the period of host absence is the main cause for this difference in selection direction. Moreover, the period of host absence seems to be the key determinant of the pathogens transmission rate. Comparing plant patho-systems with contrasting biological features suggests that airborne plant pathogen respond differently to longer periods of host absence than soil-borne plant pathogens

Pathogen Populations Evolve to Greater Race Complexity in Agricultural Systems – Evidence from Analysis of Rhynchosporium secalis Virulence Data

Fitness cost associated with pathogens carrying unnecessary virulence alleles is the fundamental assumption for preventing the emergence of complex races in plant pathogen populations but this hypothesis has rarely been tested empirically on a temporal and spatial scale which is sufficient to distinguish evolutionary signals from experimental error. We analyzed virulence characteristics of ∼1000 isolates of the barley pathogen Rhynchosporium secalis collected from different parts of the United Kingdom between 1984 and 2005. We found a gradual increase in race complexity over time with a significant correlation between sampling date and race complexity of the pathogen (r20 = 0.71, p = 0.0002) and an average loss of 0.1 avirulence alleles (corresponding to an average gain of 0.1 virulence alleles) each year. We also found a positive and significant correlation between barley cultivar diversity and R. secalis virulence variation. The conditions assumed to favour complex races were not present in the United Kingdom and we hypothesize that the increase in race complexity is attributable to the combination of natural selection and genetic drift. Host resistance selects for corresponding virulence alleles to fixation or dominant frequency. Because of the weak fitness penalty of carrying the unnecessary virulence alleles, genetic drift associated with other evolutionary forces such as hitch-hiking maintains the frequency of the dominant virulence alleles even after the corresponding resistance factors cease to be used

Effect of hosts on competition among clones and evidence of differential selection between pathogenic and saprophytic phases in experimental populations of the wheat pathogen Phaeosphaeria nodorum

<p>Abstract</p> <p>Background</p> <p>Monoculture, multi-cropping and wider use of highly resistant cultivars have been proposed as mechanisms to explain the elevated rate of evolution of plant pathogens in agricultural ecosystems. We used a mark-release-recapture experiment with the wheat pathogen <it>Phaeosphaeria nodorum </it>to evaluate the impact of two of these mechanisms on the evolution of a pathogen population. Nine <it>P. nodorum </it>isolates marked with ten microsatellite markers and one minisatellite were released onto five replicated host populations to initiate epidemics of Stagonospora nodorum leaf blotch. The experiment was carried out over two consecutive host growing seasons and two pathogen collections were made during each season.</p> <p>Results</p> <p>A total of 637 pathogen isolates matching the marked inoculants were recovered from inoculated plots over two years. Genetic diversity in the host populations affected the evolution of the corresponding <it>P. nodorum </it>populations. In the cultivar mixture the relative frequencies of inoculants did not change over the course of the experiment and the pathogen exhibited a low variation in selection coefficients.</p> <p>Conclusions</p> <p>Our results support the hypothesis that increasing genetic heterogeneity in host populations may retard the rate of evolution in associated pathogen populations. Our experiment also provides indirect evidence of fitness costs associated with host specialization in <it>P. nodorum </it>as indicated by differential selection during the pathogenic and saprophytic phases.</p

Yam: a neglected and underutilized crop in Brazil Inhame: uma cultura negligenciada e subutilizada no Brasil

In Brazil current studies and investments on yams are incipient. Similarly, the literature in recent decades lacks adequate information on this group of plants. The existing literature, on its turn, requires more than ever to be revised and organized. Yams have joined the so-called "neglected" group of crops for several reasons, but particularly because they are associated with poor and traditional communities. Many vegetables introduced in Brazil during the colonization period have adapted to different cropping systems, yams being an excellent example. This diversity resulted very widespread, yet poorly recognized in the country. In turn, the gardens using traditional farming systems continue to maintain and enhance yam local varieties. Studies from other countries, with an emphasis on characterization and genetic breeding, brought to light an urgent need for Brazil to invest in yams as a food rich in carbohydrates, even to the point of alterations in food public policy. Reversal of the yam's current stigma is both a challenge to the scientific community and to the population as a whole. This paper aims to raise pertinent questions about Dioscorea species, an important key group for many communities in tropical countries, yet still unrecognized as so in Brazil.<br>No Brasil, estudos e investimentos ao inhame são incipientes. Similarmente, a literatura nas últimas décadas apresenta informações insuficientes para este grupo de plantas. A literatura existente, por sua vez, exige mais que nunca ser revisada e organizada. O inhame tem-se unido ao grupo de culturas ditas "negligenciadas" por diversas razões, mas particularmente devido ao fato de estar associado às comunidades pobres e tradicionais. Muitos vegetais introduzidos no Brasil durante o período da colonização têm-se adaptado a diferentes sistemas de cultivo, sendo o inhame um excelente exemplo. Esta diversidade é resultado de uma ampla dispersão, ainda pouco conhecida no país. Por sua vez, as roças usam o sistema de agricultura tradicional de forma a manter e aumentar as variedades locais de inhame. Estudos de outros países, com ênfase na caracterização e melhoramento genético, trouxeram à luz uma necessidade urgente de o Brasil investir em inhame como uma rica fonte de carboidratos, mesmo apesar das mudanças na política alimentar pública. Reverter o atual estigma do inhame é um duplo desafio para a comunidade científica e população como um todo. Este artigo objetiva-se a trazer questões pertinentes sobre as espécies do gênero Dioscorea, um importante grupo para muitas comunidades em países tropicais, contudo ainda pouco conhecido no Brasil