Ground Cover North : Ground Cover 073 March-April 2008 - North
stages and is more likely to be affected by environmental factors including temperature and plant stress. These characteristics make identification and variety disease rating problematic and, in part, explains why disease ratings can differ between states. A good example is WyalkatchemA, which has been frequently seen in South Australia to be susceptible, or even highly susceptible, to stripe rust during August and September, whereas at later growth stages, and possibly at higher temperatures, its resistance appears to be much more effective and it may be rated as MR--MS (moderately resistant -- moderately susceptible) or better. In SA, disease ratings for the rusts have, where possible, been given to provide growers with appropriate advice for the time when fungicide sprays are required, rather than later in the season when APR is more fully expressed. While most genes for seedling resistance in cereals have been identified this is not the case for the minor genes. Despite some difficulties in working with them, minor genes do play an important part in providing the disease resistance of many current wheat and barley varieties for a range of fungal pathogens. MARCH -- APRIL 2008 GROUND COVER 5 Understanding disease/News Seedling and adult plant resistance Improved knowledge of cereal disease resistance is helping researchers understand and work to overcome resistance breakdown BY HUGH WALLWORK n Cereal pathologists generally use two categories to describe the disease resistance expressed by a host plant. For simplicity and differentiation these have been termed 'seedling resistance' and 'adult plant resistance'. Despite the name, seedling resistance is effective at the seedling stage, but generally continues to give protection throughout the plant's life. It is almost always controlled by a single 'major' gene that provides the strong resistance in varieties rated 'R' (resistant). Due to their level of protection and ease of use, these genes have in the past been preferentially used by plant breeders for controlling rusts. However, the disadvantage of seedling resistance is that once a pathogen overcomes this type of resistance, which is more likely to occur when inoculum levels are high, the variety often becomes completely susceptible. Adult plant resistance (APR) is not effective in the seedling stage, but increases in effectiveness as the plant matures. Typically, it is controlled by one or more 'minor' genes. Individually, these genes provide much less effective resistance than major genes, but when in combination minor genes can provide more effective and often more durable resistance. However, genes for APR provide plant breeders with several challenges. The level of resistance they provide is very variable: it can start to be expressed at different growth VAULT READY TO SAVE THE WORLD'S SEED n The Svalbard Global Seed Vault in the Arctic Circle has opened for business with the arrival of 230,000 seed samples of crop varieties from the germplasm banks of the Consultative Group on International Agricultural Research (CGIAR), including the International Maize and Wheat Improvement Center (CIMMYT), which sent three tonnes of seed for storage. The CIMMYT shipment comprised 10,000 maize and 47,000 wheat samples representing about a third of CIMMYT's collection of crop genetic resources. The Svalbard vault has been built as a safe repository of the world's food crops. Seed will be stored at –18˚C deep inside a permafrost-covered mountain. Cary Fowler, executive director of the Rome-based and GRDC-supported Global Crop Diversity Trust, which has partnered with the Norwegian Government and the Nordic Gene Bank to build the vault, says it has been designed to store seed safely for centuries: "At these temperatures, seeds for crops like wheat, barley and peas can last for up to 10,000 years." With its capacity to hold up to 4.5 million seed samples, the vault will eventually house virtually all varieties of almost every important food crop in the world. The collection is intended as a hedge against disaster, so that food production can be restarted anywhere on the planet. "We ran a lot of computer simulations to determine the optimum approach and believe we have found an effective and energy-efficient way to establish reliably cool conditions inside the vault," says project manager Magnus Bredeli. He says the design of the facility would ensure that the seeds stayed well preserved even if global warming caused outside temperatures to rise. Engineers are essentially using rock as a "cold store" he says, an approach that has become popular on the Norwegian mainland as a way to establish energy- efficient refrigeration systems. The vault sits at the end of a 120-metre tunnel, blasted in a mountain near the town of Longyearbyen on the island of Spitsbergen within the Arctic circle. Mr Tveiten says the rock should stay cold enough to allow a –18˚C temperature in the vault to be maintained by a small, 10-kilowatt refrigeration system, naturally aided by the area's permafrost and snow and ice that covers the mountain for much of the year. The GRDC has committed $1 million a year for five years to the project. More information: www.seedvault.no; www.croptrust.org The differentiation between seedling and adult plant resistance is not always sustained. For some diseases, minor genes have also been found to confer resistance at the seedling as well as adult stages. This is particularly the case for yellow leaf spot in wheat and spot-form net blotch in barley. Research has established that minor genes for APR can work through a range of mechanisms in the plant. As some minor genes that control APR may lose their effectiveness just as readily as seedling resistance genes, researchers are working to produce varieties with three or more minor genes for each rust disease. This technique is called 'pyramiding' and has been an aim of the International Maize and Wheat Improvement Center (CIMMYT) wheat-breeding program in Mexico. Using pyramiding they have successfully introduced up to four minor genes into a single variety to achieve very effective and, it is anticipated, durable leaf and stripe rust resistance. GRDC Research Code DAS00048 More information: Dr Hugh Wallwork, leader -- wheat and barley improvement, SARDI, 08 8303 9382, firstname.lastname@example.org Dr Hugh Wallwork reports that many of the minor genes that confer adult plant resistance have yet to be found. PHOTO: EMMA LEONARD The Svalbard Global Seed Vault during construction. PAGE 2 INTRODUCTION PAGE 3 STRANGE MUTATIONS PAGE 5 WHAT IS A PATHOTYPE? PAGE 6 DURABLE RESISTANCE PAGE 8 BREEDING DOES NOT OVERRIDE DISEASE MANAGEMENT PAGE 9 TRIPLE-RESISTANT MUNGBEANS PAGE 10 TRAPPING DISEASE ON THE WIND PAGE 10 BEAN DISEASE SURVEY PAGE 12 FORECASTING DISEASE RISK PAGE 13 SETTING UP THE CROP PAGE 14 A NEW SPIN ON BLACKLEG MANAGEMENT PAGE 15 FUNGICIDE RESISTANCE STRATEGY PAGE 15 BARLEY LEAF DISEASE MANAGEMENT OPTIONS PAGE 16 COST-EFFECTIVE FUNGICIDE TREATMENTS PAGE 18 EXTERNAL AND INTERNAL DISEASE THREATS PAGE 19 WORLDWIDE FIGHT AGAINST RUST Research push on disease resistance FOLIAR FUNGAL DISEASES SUPPLEMENT MARCH -- APRIL 2008 READ MORE: 20-PAGE FOLIAR FUNGAL DISEASES SUPPLEMENT WITH THIS ISSUE OF GROUND COVER HYBRID TECHNOLOGY THAT YIELDS High performance seed produces high performance crops Pioneer 's Clearfield canola hybrids have exceptional vigour and consistently deliver higher yield than open-pollinated canola varieties. Our canola hybrids are treated with Betta Strike® seed treatment as standard to help you realise their full potential. So grow Pioneer® brand canola hybrids this season and you will soon see that it is hybrid technology that yields. Make sure your crop is out in front. Grow Pioneer® brand canola hybrids this season. For more information contact your local Pioneer area manager or call 1800 CANOLA. RRA/PIO5220 45Y77 46Y78 Purchase any Pioneer® brand canola hybrid treated with Betta Strike® and you could win a trip to the 2008 Lexmark Indy 300 on the Gold Coast. Entry forms are available on Pioneer® brand canola hybrid seed bags. Full terms and conditions are at australia.pioneer.com Authorised under NSW Permit No. LTPS/08/00245; SA Permit No. T08/269. ®, TM, SM: Trademarks and service marks of Pioneer Hi-Bred International, Inc. Clearfield is a trademark of BASF.
Ground Cover 072 January-February 2008 - North
Ground Cover 074 May-June 2008 - North