Pathotype variation of barley powdery mildew in Western Australia

Barley powdery mildew caused by the fungus Blumeria graminis f. sp. hordei (Bgh) has emerged as the most damaging disease of barley in Western Australia (WA). Many of the available cultivars display high levels of disease in the field when climatic conditions are conducive. As a result, fungicides have become the main method of disease control in the last 10 years. Different types and sources of genetic disease resistance are available but to optimise their deployment it is necessary to evaluate the spectrum of pathotypes present in the pathogen population. Sixty isolates of Bgh were collected in the 2009 season from 9 locations, single spored and characterised by infection on reference barley lines and cultivars. Eighteen unique pathotypes were resolved. Virulence against many of the R-genes in the reference lines was present in at least one pathotype. Isolates were virulent against 16 out of a total of 23 resistance gene combinations. Undefeated resistance genes included the major R-genes Mla-6, Mla-9, Ml-ra and the combinations of Mla-1 plus Mla-A12 and Mla-6 plus Mla-14 and Mla-13 plus Ml-Ru3 together with the recessive resistance gene mlo-5. There was significant pathotype spatial differentiation suggesting limited gene flow between different regions with WA or localised selection pressures and proliferation. On the basis of the results we recommend a number of strategies to manage powdery mildew disease levels within WA

Pests, pesticide use and alternative options in European maize production: current status and future prospects

Political efforts are made in the European Union (EU) to reduce pesticide use and to increase the implementation of integrated pest management (IPM). Within the EU project ENDURE, research priorities on pesticide reduction are defined. Using maize, one of the most important crops in Europe, as a case study, we identified the most serious weeds, arthropod pests, and fungal diseases as well as classes and amounts of pesticides applied. Data for 11 European maize growing regions were collected from databases, publications and expert estimates. Silage maize dominates in northern Europe and grain production in central and southern Europe. Crop rotations range from continuous growing of maize over several years to well-planned rotation systems. Weeds, arthropod pests and fungal diseases cause economic losses in most regions, even though differences exist between northern countries and central and southern Europe. Several weed and arthropod species cause increasing problems, illustrating that the goal of reducing chemical pesticide applications is challenging. Pesticides could potentially be reduced by the choice of varieties including genetically modified hybrids, cultural control including crop rotation, biological control, optimized application techniques for chemicals, and the development of more specific treatments. However, restrictions in the availability of alternative pest control measures, farm organization, and the training and knowledge of farmers need to be overcome before the adoption of environmentally friendly pest control strategies can reduce chemical pesticides in an economically competitive way. The complex of several problems that need to be tackled simultaneously and the link between different control measures demonstrates the need for IPM approaches, where pest control is seen in the context of the cropping system and on a regional scale. Multicriteria assessments and decision support systems combined with pest monitoring programs may help to develop region-specific and sustainable strategies that are harmonized within a EU framework

Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors

Parastagonospora nodorum is a major fungal pathogen of wheat in Australia causing septoria nodorum blotch (SNB). P. nodorum virulence is quantitative and depends to a large extent on multiple effector-host sensitivity gene interactions. The pathogen utilises a series of proteinaceous necrotrophic effectors to facilitate disease development on wheat cultivars that possess appropriate dominant sensitivity loci. Thus far, three necrotrophic effector genes have been cloned. Proteins derived from these genes were used to identify wheat cultivars that confer effector sensitivity. The goal of the study was to determine if effector sensitivity could be used to enhance breeding for SNB resistance. In this study, we have demonstrated that SnTox1 effector sensitivity is common in current commercial Western Australian wheat cultivars. Thirty-three of 46 cultivars showed evidence of sensitivity to SnTox1. Of these, 19 showed moderate or strong chlorotic/necrotic responses to SnTox1. Thirteen were completely insensitive to SnTox1. Disease susceptibility was most closely associated with SnTox3 sensitivity. In addition, we have identified biochemical evidence of a novel chlorosis-inducing protein or proteins in P. nodorum culture filtrates unmasked in strains that lack expression of ToxA, SnTox1 and SnTox3 activities

Global genomic analyses of wheat powdery mildew reveal association of pathogen spread with historical human migration and trade

The fungus Blumeria graminis f. sp. tritici causes wheat powdery mildew disease. Here, we study its spread and evolution by analyzing a global sample of 172 mildew genomes. Our analyses show that B.g. tritici emerged in the Fertile Crescent during wheat domestication. After it spread throughout Eurasia, colonization brought it to America, where it hybridized with unknown grass mildew species. Recent trade brought USA strains to Japan, and European strains to China. In both places, they hybridized with local ancestral strains. Thus, although mildew spreads by wind regionally, our results indicate that humans drove its global spread throughout history and that mildew rapidly evolved through hybridization

Predicting Landscape-Genetic Consequences of Habitat Loss, Fragmentation and Mobility for Multiple Species of Woodland Birds

Inference concerning the impact of habitat fragmentation on dispersal and gene flow is a key theme in landscape genetics. Recently, the ability of established approaches to identify reliably the differential effects of landscape structure (e.g. land-cover composition, remnant vegetation configuration and extent) on the mobility of organisms has been questioned. More explicit methods of predicting and testing for such effects must move beyond post hoc explanations for single landscapes and species. Here, we document a process for making a priori predictions, using existing spatial and ecological data and expert opinion, of the effects of landscape structure on genetic structure of multiple species across replicated landscape blocks. We compare the results of two common methods for estimating the influence of landscape structure on effective distance: least-cost path analysis and isolation-by-resistance. We present a series of alternative models of genetic connectivity in the study area, represented by different landscape resistance surfaces for calculating effective distance, and identify appropriate null models. The process is applied to ten species of sympatric woodland-dependant birds. For each species, we rank a priori the expectation of fit of genetic response to the models according to the expected response of birds to loss of structural connectivity and landscape-scale tree-cover. These rankings (our hypotheses) are presented for testing with empirical genetic data in a subsequent contribution. We propose that this replicated landscape, multi-species approach offers a robust method for identifying the likely effects of landscape fragmentation on dispersal

Pyramiding two genes for leaf rust and powdery mildew resistance in common wheat

Leaf rust, caused by Puccinia recondita f. sp. tritici, and powdery mildew, caused by Blumeria graminis f. sp. tritici, are the most prevalent of all of the wheat diseases in many regions of the world including Poland. These two diseases can cause serious epidemics in Poland. The aim of presented research was pyramiding of leaf rust and powdery mildew resistance genes in a one genotype. A leaf rust resistance gene Lr41, derived from Triticum tauschii (syn. Aegilops squarrosa) and powdery mildew resistance gene, derived from Dasypyrum villosum (syn. Haynaldia villosa), were successfully transferred into the polish winter wheat variety. A line KS90WGRC10 was used as the resistance source of Lr41 for leaf rust and the 6VS/6AL translocation line Yangmai 5 was used as the resistance source of Pm21 for powdery mildew. In foreground selection several molecular markers for Lr41 (Gdm35, Barc124, Gwm261, Gwm296 and Gwm210) and Pm21 (SCAR1250, SCAR1400 and NAU/xibao) were applied. After the first backcrosses (BC1F1), background selection was conducted using a set of 5 AFLP primer combinations. In addition, for the screening of the BC1F2 and BC1F3 population, selected lines were inoculated in the greenhouse at the three-leaf stage with a natural pathogen population of P. recondita and B. graminis. The marker-assisted selection and pathology test allowed us to obtain homozygous lines carrying two resistance genes to leaf rust and powdery mildew in winter wheat

Evaluating barley landraces collected in North Africa and the Middle East for powdery mildew infection at seedling and adult plant stages

Barley (Hordeum vulgare L.) is one of the most widely grown cereal crops. Numerous pathogens impair the amount and quality of the grain yield. Blumeria graminis f. sp. hordei (Bgh) is a fungal pathogen causing powdery mildew, a widespread and economically important foliar disease. Since there is a limited number of known resistance genes, eforts of scientists and breeders are focused on searching for new sources of resistance. Barley landraces are a known, but still underexploited source of diversity. A set of 79 barley landraces collected in North Africa and the Middle East was tested against powdery mildew at seedling and adult plant stages. Under a controlled environment, 50% of accessions showed resistance conditioned by major genes. Among them, seven accessions showed broad resistance to Bgh isolates that were virulent to most of the known resistance genes. The feld experiments carried out under natural infection over several years indicated all accessions as potential sources for resistance breeding. Twelve landraces were found to be medium resistant or resistant during all six seasons. This report relates to barley landraces as a promising source of potentially novel resistance to powdery mildew

Use of random amplified polymorphic DNA [RAPD] assay for differentiation among isolates of Stagonospora spp. and Septoria tritici

The genetic similarity of three species: Septoria tritici, Stagonospora nodorum and Stagonospora avenae f. sp. triticea - important pathogens in many cereal production areas worldwide was assessed by random amplified polymorphic DNA (RAPD) assay. In preliminary research DNA of 14, 9, and 7 monopyenidios- pore isolates of S. nodorum, S. tritici, and S. a. tritícea, respectively, were amplified by PCR with four primers. Afterwards the research was focused on three mono- pyenidiospore isolates from each species studied. The isolates of each species selected for the study varied in pathogenicity and were diverse geographically. PCR with the set of 14 selected primers resulted in 99 different bands, ranged from 180 to 2500 base pairs in length. Most primers in PCR (especially RAD11, RAD31, RAD32, RAD33) revealed uniform bands for isolates of S. a. tritícea, that allow to identify this species among the others. The cluster analysis using Unweighed Pair-Group Method with Averaging (UPGMA) revealed interspecies disagreement among the isolates ranging from 32 to 53%. The intraspecies disagreement ranges were 17-20%, 38-43%, 42-44% for S. avenae f. sp. triticea, S. nodorum and S. tritici, respectively. Cluster analysis classified isolates into three homogeneous clusters. Each cluster grouped isolates of one species according to their current taxonomie ranks based on spore size, colony morphology and host ranges. In addition, two of the clusters represented by isolates of S. nodorum and S. a. tritícea were distinctly separated at a lower linkage distance from the third one comprising isolates of S. tritici. A slight inconsistency found in grouping some isolates indicates that such groupings should be done with caution. The present study indicates that the PCR- RAPD assay is of a potential use in taxonomy of Stagonospora spp. and Septoria tritici as well as in molecular identification of casual disease agents