Cereal Diseases Research Articles

Frequency of resistance to stem rust race TPMK in Afghan wheat cultivars

Stem rust caused by Puccinia graminis f. sp. tritici is one of the most destructive diseases of wheat (Triticum aestivum). In Afghanistan, wheat is an economically important crop, comprising approximately 80% of grain production. Little work has been done to identify Afghan wheat cultivars that are potential sources of stem rust resistance. Five modern Afghan wheat cultivars and 500 wheat accessions from Afghanistan and three adjacent regions in Pakistan, Iran, and Tajikistan were screened at the seedling stage for resistance to stem rust race TPMK. Four of the five modern Afghan cultivars (‘Hazardana’, ‘Kabul-2000’, ‘Solh-02’, and ‘Zardana’) displayed infection type 2 and were considered resistant. The four resistant lines were further evaluated at the Cereal Disease Laboratory (CDL), St. Paul, Minnesota, for resistance to seven stem rust races including TPMK (for confirmation) and TTKS (Ug99). All four lines were susceptible to race TTKS. However, ‘Hazardana’ and ‘Zardana’ were resistant to races QFCS, QTHJ, RCRS, RKQQ, and TTTT. ‘Kabul-2000’ and ‘Solh-02’ were resistant to race QFCS but susceptible to races QTHJ, RCRS, RKQQ, and TTTT. All four cultivars were confirmed at the CDL to be resistant to race TPMK. The susceptibility to race TPMK in all accessions and in one modern Afghan cultivar and the susceptibility to race TTKS in all four cultivars that were resistant to race TPMK indicate a high vulnerability of wheat lines to emerging P. graminis strains both in Afghanistan and adjacent regions.

Does vacuum-packaging or co-delivered amendments enhance shelf-life of Striga-mycoherbicidal products containing Fusarium oxysporum f. sp. strigae during storage?

The effect of vacuum packaging on the shelf-life and handling of Pesta granules and seed treatment made with chlamydospores of Fusarium oxysporum strains Foxy2, PSM197 or their mixture was studied at 4°C and 22±3°C over 1 year. In addition, the effects of co-incorporated amendments [urea in Pesta or co-delivered fungicides (Ridomil Gold®, Apron XL®) on coated sorghum seeds], and coating material (Arabic gum ‘AG’, SUET Binder ‘SB’) on the viability of Striga-mycoherbicides were evaluated. Storage under vacuum packaging did not enhance shelf-life of the formulated Striga-mycoherbicidal products after 12 months of storage regardless of the treatment used. The co-incorporated urea into Pesta granules significantly reduced the viability of mycoherbicides, but less so at 4°C (58% strain-stability after 12 months). No significant differences between the coating materials in maintaining the viability of mycoherbicides were observed. The shelf-life of isolates on coated seeds significantly decreased when adding Ridomil Gold®. However, at 4°C, the fungicide Apron XL® allowed better survival of Foxy2 and PSM197 by maintaining their averaged half-lives (t 0.5) by an additional 6 months compared to Ridomil Gold®. In general, Striga-mycoherbicidal product combinations exhibited a significantly higher shelf-life when stored at 4°C than at 22±3°C. The absence of a positive effect of vacuum packaging on shelf-life of Striga-mycoherbicidal products reflects the tolerance of the formulated fungal propagules (chlamydospores) to withstand an oxygen enriched environment and allows their handling and distribution through ordinary packaging systems in Africa. The high compatibility between Striga-mycoherbicides and the co-delivered fungicide Apron XL®, and the fungal storage stability allows simultaneous control of Striga and fungal cereal diseases within an integrated pest management (IPM).

The identification of candidate genes associated with Pch2 eyespot resistance in wheat using cDNA-AFLP

Eyespot is a fungal disease of the stem base of cereal crops and causes lodging and the premature ripening of grain. Wheat cultivar Cappelle Desprez contains a highly durable eyespot resistance gene, Pch2 on the long arm of chromosome 7A. A cDNA-amplified fragment length polymorphism (AFLP) platform was used to identify genes differentially expressed between the eyespot susceptible variety Chinese Spring (CS) and the CS chromosome substitution line Cappelle Desprez 7A (CS/CD7A) which contains Pch2. Induced and constitutive gene expression was examined to compare differences between non-infected and plants infected with Oculimacula acuformis. Only 34 of approximately 4,700 cDNA-AFLP fragments were differentially expressed between CS and CS/CD7A. Clones were obtained for 29 fragments, of which four had homology to proteins involved with plant defence responses. Fourteen clones mapped to chromosome 7A and three of these mapped in the region of Pch2 making them putative candidates for involvement in eyespot resistance. Of particular importance are two fragments; 4CD7A8 and 19CD7A4, which have homology to an Oryza sativa putative callose synthase protein and a putative cereal cyst nematode NBS-LRR disease resistance protein (RCCN) respectively. Differential expression associated with Pch2 was examined by semi-quantitative RT-PCR. Of those genes tested, only four were differentially expressed at 14 days post inoculation. We therefore suggest that a majority of the differences in the cDNA-AFLP profiles are due to allelic polymorphisms between CS and CD alleles rather than differences in expression.

Effect of preceding crops on the winter cereal productivity and diseases incidence

Experiments were carried out in the Vežaiciai Branch of the Lithuanian Institute of Agriculture (West Lithuania region) in 2002-2005. The aim of this research was to estimate the ecological significance of perennial legumes used as green manure for the biological properties of triticale and rye and for diseases resistance. Residues of the perennial grasses tested and ploughed-in aftermath contributed different contents of nitrogen to the soil. The highest content of nitrogen was contributed to the soil with red clover residues and aftermath. Residues of white clover and aftermath ploughed in as green manure determined more favourable soil properties. This had a positive effect on the formation of biological parameters of cereals grown after white clover, which made it possible without mineral and organic fertilisers to produce on average 3.88 t ha-1 of triticale grain and 3.82 t ha-1 of rye grain, or by 1.09 and 0.28 t ha-1 more compared with their growing after red clover managed in the same way as white clover. Different growing conditions of winter cereals, i.e. different preceding crops, had a significant effect on the occurrence of scald and septoriosis.

Poor adoption of ley-pastures in south-west Queensland: biophysical, economic and social constraints

The present review identifies various constraints relating to poor adoption of ley-pastures in south-west Queensland, and suggests changes in research, development and extension efforts for improved adoption. The constraints include biophysical, economic and social constraints. In terms of biophysical constraints, first, shallower soil profiles with subsoil constraints (salt and sodicity), unpredictable rainfall, drier conditions with higher soil temperature and evaporative demand in summer, and frost and subzero temperature in winter, frequently result in a failure of established, or establishing, pastures. Second, there are limited options for legumes in a ley-pasture, with the legumes currently being mostly winter-active legumes such as lucerne and medics. Winter-active legumes are ineffective in improving soil conditions in a region with summer-dominant rainfall. Third, most grain growers are reluctant to include grasses in their ley-pasture mix, which can be uneconomical for various reasons, including nitrogen immobilisation, carryover of cereal diseases and depressed yields of the following cereal crops. Fourth, a severe depletion of soil water following perennial ley-pastures (grass + legumes or lucerne) can reduce the yields of subsequent crops for several seasons, and the practice of longer fallows to increase soil water storage may be uneconomical and damaging to the environment. Economic assessments of integrating medium- to long-term ley-pastures into cropping regions are generally less attractive because of reduced capital flow, increased capital investment, economic loss associated with establishment and termination phases of ley-pastures, and lost opportunities for cropping in a favourable season. Income from livestock on ley-pastures and soil productivity gains to subsequent crops in rotation may not be comparable to cropping when grain prices are high. However, the economic benefits of ley-pastures may be underestimated, because of unaccounted environmental benefits such as enhanced water use, and reduced soil erosion from summer-dominant rainfall, and therefore, this requires further investigation. In terms of social constraints, the risk of poor and unreliable establishment and persistence, uncertainties in economic and environmental benefits, the complicated process of changing from crop to ley-pastures and vice versa, and the additional labour and management requirements of livestock, present growers socially unattractive and complex decision-making processes for considering adoption of an existing medium- to long-term ley-pasture technology. It is essential that research, development and extension efforts should consider that new ley-pasture options, such as incorporation of a short-term summer forage legume, need to be less risky in establishment, productive in a region with prevailing biophysical constraints, economically viable, less complex and highly flexible in the change-over processes, and socially attractive to growers for adoption in south-west Queensland.

The emergence of cereal fungal diseases and the incidence of leaf spot diseases in Finland

Fungal plant pathogens causing cereal diseases in Finland have been studied by a literature survey, and a field survey of cereal leaf spot diseases conducted in 2009. Fifty-seven cereal fungal diseases have been identified in Finland. The first available references on different cereal fungal pathogens were published in 1868 and the most recent reports are on the emergence of Ramularia collo-cygni and Fusarium langsethiae in 2001. The incidence of cereal leaf spot diseases has increased during the last 40 years. Based on the field survey done in 2009 in Finland, Pyrenophora teres was present in 86%, Cochliobolus sativus in 90% and Rhynchosporium secalis in 52% of the investigated barley fields. Mycosphaerella graminicola was identified for the first time in Finnish spring wheat fields, being present in 6% of the studied fields. Stagonospora nodorum was present in 98% and Pyrenophora tritici-repentis in 94% of spring wheat fields. Oat fields had the fewest fungal diseases. Pyrenophora chaetomioides was present in 63% and Cochliobolus sativus in 25% of the oat fields studied.;

Legumes in Finnish agriculture: history, present status and future prospects

Legumes are important in world agriculture, providing biologically fixed nitrogen, breaking cereal disease cycles and contributing locally grown food and feed, including forage. Pea and faba bean were grown by early farmers in Finland, with remains dated to 500 BC. Landraces of pea and faba bean were gradually replaced by better adapted, higher quality materials for food use. While grain legumes have been restricted by their long growing seasons to the south of the country, red, white and alsike clovers are native throughout and have long been used in leys for grazing, hay and silage. Breeding programmes released many cultivars of these crops during the 1900s, particularly pea and red clover. A.I. Virtanen earned the 1945 Nobel Prize in Chemistry for his work on both nitrogen fixation and silage preservation. Use of crop mixtures may appear modern, but farmers used them already in the early 1800s, when oat was used to support pea, and much effort has been devoted to improving the system and establishing its other benefits. Although international cultivars have been easily accessible since Finland’s 1995 entry into the European Union, the combination of feed quality and appropriate earliness is still needed, as < 1% of arable land is sown to grain legumes and an increase to 9–10% would allow replacement of imported protein feeds. Climate change will alter the stresses on legume crops, and investment in agronomy, physiology and breeding is needed so that farmers can gain from the many advantages of a legume-supported rotation.;

Systemic stem infection by Fusarium species in barley and wheat

Fusarium head blight, caused by Fusarium species, is an important disease of cereals in western Canada. There are conflicting results in the literature regarding the infection pathway leading to disease development. The present study was undertaken to evaluate the potential for systemic infection in barley (Hordeum vulgare) by artificially inoculating F. graminearum and F. pseudograminearum into the growth medium in pots containing seeds or seedlings of 'AC Lacombe' and 'Chevron' barley. Furthermore, naturally infected barley and wheat (Triticum aestivum) kernels were grown to assess the potential for systemic infection by F. graminearum from seed into the stem. Approximately 50% of naturally infected seeds either failed to emerge, or the seedlings died shortly after emergence. Crown and stem discolouration developed on the inoculated barley and naturally infected wheat seed. Mycelial growth and sporulation were observed in the crown area using light and electron microscopy. Fusarium graminearum and F. pseudograminearum were identified through isolation. Systemic infection was confirmed by isolation from up to 31% of the wheat culm segments and was past the third node, which exceeded the extent of discolouration of the third internode assessed by visual examination. Fungal hyphae were mostly located in the parenchyma tissue of the culm, with few observed in the vascular tissue. No head blight symptoms resulting from seed infection were observed. In conclusion, no evidence was found for systemic infection from seed or belowground plant tissues that resulted in head blight of barley or wheat using the current inoculation methods and under the current experimental conditions. In the growth chamber, seed and seedling infection by F. graminearum and F. pseudograminearum and subsequent systemic infection can lead to infection of the lower stem. It is still unclear if similar results occur under field conditions. Key words: Fusarium graminearum, Fusarium pseudograminearum, seed inoculation. La fusariose de l'épi (FHB), causée par des espèces de Fusarium, est une maladie majeure qui s'attaque aux céréales de l'Ouest canadien. Les conclusions que l'on trouve dans la littérature relativement aux modes de propagation de l'infection qui mènent au développement de la maladie sont contradictoires. La présente étude a été entreprise afin d'évaluer la possibilité de provoquer une infection systémique chez l'orge (Hordeum vulgare) en inoculant F. graminearum et F. pseudograminearum dans le support de culture contenu dans des pots hébergeant des semences ou des plantules de cultivars d'orge 'AC Lacombe' et 'Chevron'. De plus, des grains d'orge et de blé (Triticum aestivum) infectés naturellement ont été cultivés afin d'évaluer la capacité de F. graminearum à provoquer l'infection systémique des tiges par l'entremise des semences. Environ 50 % des semences infectées naturellement n'ont soit pas germé ou sont mortes peu après avoir germé. Les couronnes et les tiges des plants issus de semences d'orge inoculées et de semences de blé infectées naturellement ont affiché un changement de coloration. On a pu observer la croissance mycélienne et la sporulation par microscopie photonique et électronique. Fusarium graminearum et F. pseudograminearum ont été identifiés par isolement. L'infection systémique a été confirmée par isolement dans près de 31 % des segments de chaume de blé et elle avait dépassé le troisième nœud, ce qui excédait l'étendue du changement de coloration du troisième entrenœud observé à l'œil nu. L'hyphe fongique était principalement localizé dans les tissus du parenchyme du chaume, quoiqu'on l'ait également observé dans les tissus vasculaires. Aucun symptôme de la fusariose de l'épi résultant de l'infection des semences n'a été observé. Finalement, aucune évidence d'infection systémique causée par des semences ou des tissus hypogés qui aurait provoqué la fusariose de l'épi chez l'orge ou le blé n'a été démontrée, et ce, en faisant appel aux méthodes usuelles d'inoculation, selon les conditions expérimentales courantes. Dans la chambre de culture, l'infection de semences et de plantules par F. graminearum et F. pseudograminearum, et l'infection systémique qui en résulte, peut affecter la partie inférieure de la tige. Par ailleurs, on ne sait toujours pas si l'on peut s'attendre aux mêmes résultats dans des conditions naturelles. Mots-clés : Fusarium graminearum, Fusarium pseudograminearum, inoculation des semences.

Spatial distribution of Fusarium Head Blight pathogens and associated mycotoxins in wheat fields

Fusarium Head Blight (FHB) is one the most important diseases in small grain cereals and often is caused by a complex of Fusarium species. Some of these species are able to produce one or several mycotoxins. The spatial distribution of the disease and associated mycotoxins was examined in this study. Results were mapped and analysed with a geographic information system (GIS). Correlations between the incidence of the deoxynivalenol (DON) producing Fusarium species and DON contamination of kernels were rather weak. The level of DON contamination seemed to be less influenced by the frequency of DON producing Fusarium species than by other factors.

Bacterium-mediated control of Fusarium head blight disease of wheat and barley and associated mycotoxin contamination of grain

Fusarium culmorum causes Fusarium head blight (FHB) disease of cereals, resulting in yield loss and contamination of grain with the trichothecene mycotoxin, deoxynivalenol (DON). In a test for potential disease control organisms, Pseudomonas fluorescens strains MKB 158 and MKB 249 and Pseudomonas frederiksbergensis strain 202 significantly reduced both the severity of FHB disease symptoms caused by F. culmorum on wheat and barley (⩾23%; P ⩽ 0.050) and the disease-associated loss in 1000-grain weight (⩾16%; P ⩽ 0.050) under both glasshouse and field conditions when applied 24 h pre-pathogen inoculation. Glasshouse studies showed that these bacteria were more effective in controlling disease when applied 24 h pre- as opposed to 24 h post-pathogen inoculation. The most striking finding was that, in the F. culmorum-inoculated field trials, treatment with either of the two P. fluorescens strains (MKB 158 or MKB 249) also significantly reduced the DON levels in wheat and barley grain (74–78%; P ⩽ 0.050). This is the first report detailing the ability of fluorescent pseudomonad bacteria to control FHB disease and simultaneously reduce mycotoxin contamination of wheat and barley under field conditions.

Comparison of the efficacy of chitosan with that of a fluorescent pseudomonad for the control of Fusarium head blight disease of cereals and associated mycotoxin contamination of grain

Fusarium culmorum can cause Fusarium head blight (FHB) disease of cereals, resulting in yield loss and contamination of grain with the trichothecene mycotoxin, deoxynivalenol (DON). In this study, we compared the efficacy of a biological control agent ( Pseudomonas fluorescens strain MKB 158) with the biochemical chitosan (the deacetylated derivative of chitin) in controlling FHB disease of wheat and barley. Both agents were equally effective in reducing DON contamination of grain caused by F. culmorum. Under both glasshouse and field conditions, treatment with commercially available crabshell-derived chitosan reduced the severity of FHB symptom development on wheat and barley by ⩾74% ( P ⩽ 0.050). While treatment with P. fluorescens reduced the severity of FHB symptom development on these cereals by ⩾48% ( P ⩽ 0.050). Chitosan and P. fluorescens respectively prevented ⩾58 and ⩾35% of the FHB-associated reductions in 1000-grain weight in wheat and barley ( P ⩽ 0.050). Both agents significantly reduced the DON content of wheat and barley under both glasshouse and field conditions ( P ⩽ 0.050) and were equally efficacious in doing so (⩾74 and ⩾79% reductions due to chitosan and P. fluorescens, respectively). Crude chitin extracts from crabshells and crude chitosan-based formulations prepared from crabshells and eggshells were also tested under field conditions, but were not as effective as the commercial crabshell-derived preparation in controlling FHB disease. This is the first report on the use of chitosan for the control of Fusarium head blight disease and DON contamination of grain.

Wheat leaf rust caused by Puccinia triticina

Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores as long as infected leaf tissue remains alive. Urediniospores can be wind-disseminated and infect host plants hundreds of kilometres from their source plant, which can result in wheat leaf rust epidemics on a continental scale. This review summarizes current knowledge of the P. triticina/wheat interaction with emphasis on the infection process, molecular aspects of pathogenicity, rust resistance genes in wheat, genetics of the host parasite interaction, and the population biology of P. triticina. Puccinia triticina Eriks.: kingdom Fungi, phylum Basidiomycota, class Urediniomycetes, order Uredinales, family Pucciniaceae, genus Puccinia. Telial/uredinial (primary) hosts: common wheat (Triticum aestivum L.), durum wheat (T. turgidum L. var. durum), cultivated emmer wheat (T. dicoccon) and wild emmer wheat (T. dicoccoides), Aegilops speltoides, goatgrass (Ae. cylindrica), and triticale (X Triticosecale). Pycnial/aecial (alternative) hosts: Thalictrum speciosissimum (= T. flavum glaucum) and Isopyrum fumaroides. Leaf rust is characterized by the uredinial stage. Uredinia are up to 1.5 mm in diameter, erumpent, round to ovoid, with orange to brown uredinia that are scattered on both the upper and the lower leaf surfaces of the primary host. Uredinia produce urediniospores that are sub-globoid, average 20 microm in diameter and are orange-brown, with up to eight germ pores scattered in thick, echinulate walls. Wheat varieties that are fully susceptible have large uredinia without causing chlorosis or necrosis in the host tissues. Resistant wheat varieties are characterized by various responses from small hypersensitive flecks to small to moderate size uredinia that may be surrounded by chlorotic and/or necrotic zones. USDA Cereal Disease Laboratory: http://www.ars.usda.gov/mwa/cdl.

Detection of cereal viruses in wheat (Triticum aestivumL.) by serological and molecular methods

The reliable monitoring of field virus infections of crop species is important for both farmers and plant breeders. The aim of this study was to detect virus infections of winter wheat in the 2006/2007 season. Twelve well-known winter wheat varieties were sown on two different dates (11 th of October and 3 rd of November 2006). Leaves of two individuals from each genotype were collected on 23rd of April 2007 to detect the virus infections (Barley stripe mosaic virus — BSMV, Barley yellow dwarf virus — BYDV-PAV, Wheat dwarf virus — WDV and Wheat streak mosaic virus — WSMV) after an extra mild autumn- and wintertime. Virus infections were detected by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). The aphid-transmitted BYDV-PAV was found frequently whereas other viruses were presented very rarely or were not detected. Forty-six per cent of the tested wheat plants proved to be infected by BYDV-PAV in ELISA, while using PCR, the virus infections with BYDV-PAV was found in 58% of the samples. Further, these results suggest that the optimal sowing time is critical in the control of cereal virus diseases, and additionally, that wheat varieties respond to the virus infections differently.

Ancient plant diseases in Roman Age

A historical approach to plant pathology has been provided on the basis of textual evidence. Roman writers on agriculture, i. e. Cato, Varro, Virgil, Pliny the Elder and Columella, have been revised, with the aim of identifying some of the plant diseases spread in the Roman Age. Rust disease of cereals was the most frequently reported, besides grape rot, root rot of fig trees and rue plants, wood decay of holly oak and, probably, Esca disease of grapevine. Insects and weeds were occasionally cited. The recorded data have been briefly discussed and compared to Greek and Biblical textual sources, while archaeological evidence has been presented to support them, although pertaining to a prehistoric context.

Induction of PR proteins and resistance by the biocontrol agent Clonostachys rosea in wheat plants infected with Fusarium culmorum

Clonostachys rosea (CR) is a common worldwide saprophyte with destructive effect against several plant pathogenic fungi showing antagonistic features against a wide variety of pathogens. We recently isolated a strain of C. rosea, named CR47, from wheat crown infected with Fusarium culmorum (FC); this strain proved to be effective against Fusarium seed borne diseases of cereals under field condition. In this paper the function of C. rosea applied as seed treatment on wheat seedling growth was investigated. In addition, we investigated the expression pattern of peroxidases and chitinases as well as PR4 proteins following both CR treatments of seeds and FC infection and also in the three-component system pathogen–antagonist–wheat. Several chitinase isoforms were induced by CR-treatment both in coleoptiles and roots, whereas some peroxidase isoforms were induced only in the presence of both antagonist and pathogen. In the latter case, it seems that CR-treatment by itself promotes plant growth and reduces the peroxidase expression, while enhances some chitinase isoforms probably involved in cell wall disruption. Moreover, both the antagonist and the pathogen studied induced PR4 protein expression, which probably exerts its role on the invading microorganisms by a translation-inhibitory process that could be ascribed to their ribonuclease activity.

Germination of Ascospores of Gibberella zeae After Exposure to Various Levels of Relative Humidity and Temperature

Fusarium head blight (FHB) is one of the most important cereal diseases in the world and has caused major losses to the grain industry. The principal pathogen causing FHB in North America is Gibberella zeae (anamorph Fusarium graminearum). Information on survival and the conditions under which ascospores remain viable once released from perithecia may assist in refining disease forecasting models. This study measured germination of ascospores after exposure to different temperatures, 15, 20, and 30 degrees C, and levels of relative humidity (RH), 30, 60, and 90% for 4, 24, or 48 h periods. Viability was tested by germination on water agar. Germination rates fell with increasing temperatures at all observation times and at all humidity levels. At 15 and 20 degrees C after 48 h, germination ranged from 74 to 85%, and 52 to 72%, respectively. At 30 degrees C, germination ranged from 36 to 59% after 24 h and from 13 to 47% after 48 h. Germination was highest at 90% RH, except at 30 degrees C after 48 h, and lowest at 60% RH. Successful germination, even under extreme conditions, suggests that ascospores are sufficiently robust to constitute a source of inoculum under most environmental conditions encountered during the growing season.

Identification of up-regulated genes during zearalenone biosynthesis in Fusarium

The Fusarium genus includes devastating plant pathogenic fungi that cause diseases in cereals around the world. They produce several mycotoxins, including the estrogenic compound zearalenone. To better understand the molecular mechanisms determining zearalenone production, we performed differential display RT-PCR under conditions where Fusarium graminearum and F. culmorum produced high amounts of zearalenone. We found 133 expressed sequence tags (ESTs) and 54 of these were considered to be up-regulated during high zearalenone production. Several of the ESTs were confirmed to be up-regulated by real-time qPCR, but none showed any significant down-regulation in the zearalenone negative mutant ΔPKS4-T9, or were similar to typical gene expression patterns of previously described zearalenone-related genes. Some of the up-regulated ESTs were similar to genes involved in secondary metabolite production, lipid metabolism, transcriptional activation, provision of precursors, signal transduction, transport or detoxification. Several of the ESTs were also located adjacent to one another in the genome and therefore might represent genes involved in the same biosynthetic pathway. Members of six such putative pathways could be found. All sequences were compared to the MIPS F. graminearum Genome Database to verify autocalled gene predictions experimentally and to introduce new exons and gene structures.

Changes in fungicide sensitivity and relative species abundance in Oculimacula yallundae and O. acuformis populations (eyespot disease of cereals) in Western Europe

Changing fungicide sensitivities in populations of Oculimacula yallundae and O. acuformis, the species responsible for cereal eyespot in Western Europe, were determined over a 17 year period between 1984 and 2000. The data were collected by Aventis Crop Science as part of their long‐term survey to monitor changes in sensitivity to prochloraz and the methyl benzimidazole carbamate (MBC) fungicides in eyespot populations. The results show evidence for reduced sensitivity to both fungicides over the period of the survey. The decline in MBC sensitivity is in agreement with reports of practical resistance (a detectable loss of disease control in the field) to this fungicide which were widely reported from the mid 1980s onward. Prochloraz sensitivity was more complex, with the emergence of a higher resistance category of isolates in the late 1980s and early 1990s which then decreased in frequency towards the end of the survey. This may be partly explained by the introduction and increased use of cyprodinil in the mid 1990s. Although all trends were similar across Europe, differences were observed between the two eyespot species. A higher frequency of O. yallundae isolates showed decreased sensitivity to MBC, whereas decreased sensitivity to prochloraz was at a higher frequency in O. acuformis populations. The relative abundance of the two eyespot species was influenced by their differential levels of fungicide sensitivity, with the ratio increasing toward the species with the highest level of resistance to the prevailing fungicide.

Canola (Brassica napus L.) seedbank declines rapidly in farmer-managed fields in South Australia

Canola is an important crop in southern Australia, where it is used as part of the crop rotation to manage cereal diseases, improve wheat yields, and assist in integrated weed management programs. The potential release of herbicide-tolerant transgenic cultivars into Australia has raised concerns that volunteer canola may itself become an uncontrollable weed. This study examined the persistence of the canola seedbank in farmer-managed fields in 3 geographical areas of the South Australian cropping region for up to 3.5 years after the last canola crop was grown. In total, 66 fields from minimum- and no-tillage farms were sampled for number of canola seed/m2 and the percentage of those that germinated. ANOVA analysis indicated that time since the last harvest and cultivation method were both significant factors affecting the number of seed/m2 present. Neither time since harvest nor cultivation method was significant for number of germinated canola seeds, although time since harvest approached significance at the 5% level. This demonstrates that the canola seedbank and the number of volunteers decline rapidly in managed cropping systems in southern Australia. Therefore, it is unlikely that herbicide-tolerant canola will become a major weed if volunteers are managed carefully.

Application and evaluation of Pseudomonas strains for biocontrol of wheat seedling blight

Microdochium nivale, the causal agent of snow mould, is a serious pathogen of many important cereal crops. This pathogen, like many related Fusarium species, causes seedling blight, foot rot and head blight diseases of cereals. Four bacterial strains showing good effect in increasing seedling emergence and in reducing disease severity in greenhouse screenings were tested in field experiments. One Pseudomonas fluorescens strain significantly improved plant establishment and harvest yield in infested winter wheat. Plant numbers were increased by up to 48% and yield by 26.5% in different field trials. Significant increases in head numbers were also observed. There was consistent and good plant protection for long periods of the growing seasons.