NatioNal variety trials supplemeNt - Grains Research ...

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Coordinated disease assessment Disease ranking for wheat and barley lines and cultivars in NVT is now carried out independently through nationally coordinated projects Weeds and disease 10 By Emma Leonard The use of varietal resistance remains at the forefront for the management of most important diseases of cereals. To ensure growers have reliable disease ratings on newly released cereal cultivars, wheat and barley pathologists are taking a very proactive approach to gathering disease data from inclusions within the National Variety Trials (NVT) evaluation system. To provide an independent disease ranking system for the commercially bred winter crops – wheat, barley and canola – the GRDC has established several projects that are run by disease experts across Australia These screening and monitoring projects include all the NVT lines prior to commercialisation as well as an agreed set of commercial cultivars. While independence remains a cornerstone of this work, good collaboration with the breeding companies is also important. Disease screening remains part of the breeding programs run by Pulse Breeding Australia, which is an unincorporated joint venture. Wheat For the past five years a coordinated disease assessment project for wheat has been applied to NVT. The project is coordinated by Dr Grant Hollaway, senior plant pathologist at the Victorian Department of Primary Industries (DPI) and NVT. With his colleagues at Horsham he coordinates all the disease rankings work for wheat, which is carried out with seven other pathology teams across Australia. The seed distributed to all collaborators is from a single source for each variety and supplied to the Victorian DPI by the breeding companies. In addition, the team maintains a current set of wheat varieties already available to growers, known as the AUSVAR set. “Each year we distribute seed for about 120 NVT lines of bread wheat, durum and triticales as well as about 100 from the AUSVAR,” Dr Hollaway explains. “Just for the Victorian component of the project we are managing field nurseries for the three rusts (stripe, leaf and stem) and yellow leaf spot. In others states the pathology groups evaluate the set of wheat lines for diseases relevant to their district and within their area of specialisation.” In total, across Australia this network of plant pathologists annually evaluates the NVT lines against 14 different diseases of wheat (Table 1). Within Australia the plant pathology groups involved in the screening include the state departments of agriculture in all mainland states and at the University of Sydney. The disease/s to be screened are agreed between the GRDC, the NVT trial management and the pathologists and are often based on the environment and the skills held by various pathologists around Australia. “Not every disease will be screened at every location, but duplicate locations help reduce the risk of unconducive seasons and enable better screening of diseases with multiple pathotypes.” In addition to trials in Australia, some material is screened in the UK, New Zealand and Mexico. This is to establish disease ratings for pathogens or pathotypes that pose potential biosecurity threats to Australia. While the pathologists observe the NVT trial plots, the data for disease ratings is collected from disease nurseries in the field, mini plots or glasshouse. To ensure the target diseases and pathotypes are present, the pathologist inoculates the trials with disease inoculum they have gathered, tested and multiplied. Data is recorded using a standard template and returned to the NVT manager. The whole process is run on a strict timetable to ensure data is available to growers at the start of the following year. A pathologist with specialist knowledge will nominate the ratings for specific diseases, based on the current and previous year’s data. Where possible, a single national rating will be assigned for each disease. Where there are pathotype differences then regional ratings are assigned as appropriate. All plant breeders and relevant parties are informed of the ratings photo: Emma Leonard Local agronomists are an important source of information about the emergence of new pathogens for pathologists. SARDI's Dr Hugh Walwork (left), who is involved in the wheat and barley screening work in South Australia, discusses a new pathotype identified by Yorke Peninsula agronomist Sam Holmes (right). Table 1 Wheat and barley diseases screened as part of the nationally coordinated, independent disease rating system for NVT Wheat Black point Bunt Cereal cyst nematode Crown rot Common root rot Flag smut Leaf rust Pratylenchus neglectus Pratylenchus thornei Powdery mildew Septoria nodorum blotch Stripe rust Septoria tritici blotch Yellow leaf spot Barley Barley yellow dwarf virus Cereal cyst nematode Common root rot (Bipolaris) Covered smut Net form net blotch Spot form net blotch Leaf rust Pratylenchus neglectus Pratylenchus thornei Barley grass stripe rust Barley stripe rust Powdery mildew Stem rust Scald Spot blotch
A new pathotype of net blotch identified on a previously resistant barley. Samples are gathered in the paddock and taken to the laboratory for multiplication and testing. prior to public release and there is a 10-day review period in which they can provide feedback. A process has been established to reassess disputed ratings. Barley A coordinated disease assessment process was implemented for barley in 2012. Greg Platz, principal pathologist at Agri-Science Queensland, coordinates this project, following the model established for wheat. Across Australia a network of 11 pathologists and technicians gather data on 15 diseases of barley (Table 1). With some of these diseases, such as leaf rust and net form net blotch, at least six different pathotypes are used, providing a comprehensive evaluation of resistance. The protocols for seed distribution, data collection and reporting mirror those used in the wheat disease screening project, although on a smaller scale. There are only 19 NVT lines and 48 released barley varieties (commonly referred to as the AUSBAR set) in the 2012 series. It is the responsibility of individual pathologists to ensure data is generated but how this is achieved is at their discretion. In disease-conducive environments natural infection will be used, while in other trials, and in the glasshouse, plants will be artificially inoculated. “We aim to characterise the diseases in as many individual nurseries as possible to understand which virulences are present. This will increase our confidence in how effective the resistances are in individual lines,” Mr Platz says. “Testing with multiple, known pathotypes also helps us determine the genes providing resistance to some pathogens. This information assists researchers in variety development and sowing recommendations. The Plant Breeding Institute at Cobbitty, NSW, currently provides this service for leaf rust and it could be expanded to other diseases in the future.” Nationally coordinated NVT disease screenings provide a comparative evaluation of a line’s performance under different environments and disease epidemics, giving increased confidence to the disease ratings applied to new varieties. This assists growers in their varietal selection and management decisions and encourages breeding entities to develop varieties with adequate multiple-disease resistance. □ GRDC Research Codes DAV00107, DAQ00161, DAS00057, DAW00199, DAQ00161 More information: Dr Grant Hollaway, senior plant pathologist – cereals, Victorian Department of Primary Industries, 03 5362 2111, grant.hollaway@dpi.vic.gov. au; Greg Platz, principal pathologist, Agri-Science Queensland, 07 4660 3633, greg.platz@daff.qld.gov.au 11 Weeds and disease Advances in blackleg management Practices to deal with the breakdown of blackleg resistance in intensive canola districts are based on large screening trials By Dr Steve Marcroft Our understanding of the blackleg pathogen of canola has progressed substantially over the past few years. An important practical development from this work is that all current commercial cultivars and advanced breeding lines have been screened to determine their complement of blackleg resistance genes. This has enabled researchers to allocate cultivars into one of seven resistance groups. Growers are familiar with the rating of crop varieties for susceptibility (S) through to resistance (R) to a specific pathogen. However, the sexually reproducing pathogen blackleg is adept at overcoming cultivar resistance, which compromises a cultivar’s blackleg rating. Field observations have found blackleg resistance is often overcome when the same variety is regularly grown across large areas in a region for more than three years. Seven resistance rotation groups have been established, named A to G. If there is a risk of high blackleg severity in a location where the same cultivar has been grown for three or more years then a cultivar from a different resistance group needs to be sown (see Blackleg Management Guide Fact Sheet, www.grdc.com.au/ GRDC-FS-BlacklegManagementGuide). One canola cultivar from each of the seven resistance groups has been sown adjacent to National Variety Trials (NVT) sites to monitor how blackleg populations evolve to overcome cultivar resistance. In 2011, this blackleg monitoring identified regional differences in infection levels between resistance groups. This information was used as the basis of a pre-sowing early warning system to alert growers in a region to the potentially high level of blackleg inoculum able to attack cultivars in a specific resistance group. There are 32 blackleg monitoring sites across Australia located in New South Wales, South Australia, Victoria and Western Australia. Blackleg Management Guide Blackleg spores are released from canola stubble and spread extensively by wind and rain splash. Therefore disease pressure is higher in areas of intensive canola production and higher rainfall. The Blackleg Management Guide, which was released as a GRDC Fact Sheet in July 2012 (www.grdc.com.au/ GRDC-FS-BlacklegManagementGuide), provides a four-step process to help growers identify and manage the risk of blackleg on a paddock-by-paddock basis. Step 1. Determine the risk for your region; Step 2. Identify the blackleg severity in each of your paddocks; Step 3. Select management practices to reduce the risk including cultivar resistance, distance from old canola stubble, fungicide use, years of the same cultivar and time of sowing; and Step 4. If you are seeing disease levels increasing in a third year of growing the same cultivar then select a cultivar from a different resistance group. □ GRDC Research Code UM00042 More information: Dr Steve Marcroft, Marcroft Grains Pathology, 03 5381 2294, steve@grainspathology.com.au
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