Ground Cover North : Ground Cover 062 June-July 2006 - North
Genes the key to barley protection Researchers are examining plant defence mechanisms against disease to develop crops with long-lasting resistance BY MICHAEL McLEAN n Genetic modification may hold the answer to coping with the rapidly-adapting fungal diseases net blotch and leaf scald. They do not cause large losses, but both diseases prevent certain regions from growing popular varieties such as GairdnerA, which suffers substantially if conditions suit these diseases. Researchers from the Molecular Plant Breeding Cooperative Research Centre say the best way to breed for disease resistance is to find genes that help the plant combat attacking pathogens. “Traditionally, when most people have bred for disease resistance, they have bred for genes that are involved in recognising that the pathogen is there,” says Dr Amanda Able. “They relied on the fact that the fungus produces a protein that the plant recognises, prompting the plant to switch on its defences. The problem with this is that the fungus can mutate, produce a different protein and then become unrecognisable to the plant.” In a similar ‘arms race’ to the one our bodies face every winter with the common cold, breeders are racing to breed resistance into commercial varieties, while their very actions are forcing pathogens to evolve into new virulent forms. Some resistance genes last a long time, but there are examples where a new variety has been released only to be outdone by the pathogen within 12 months or so. “If we’re going to spend eight to 10 years developing a variety only to put it out in the field and it collapses, we’ve just wasted all that money,” Dr Able says. “We need to make sure that what we produce lasts longer.” Dr Able and her University of Adelaide- based team have been looking at the defence mechanisms that take place after the plant recognises the disease. “We wanted to know what happens in a disease resistance response,” Dr Able says. “What sorts of things does a plant do to protect itself? We’ve found a number of genes that we know are involved in disease resistance in some form or another.” Using genetic modification, Dr Able believes it may be possible to ‘turn up’ the production of the proteins for which these genes are responsible. Another approach would be to screen established lines for the genetic markers that show which plants are already producing high levels of the proteins. “The idea is that if we can over- express them, then hopefully the disease resistance will be there all the time: it won’t rely on recognition.” One of the major causes of damage to plant tissue during infection is caused by the plant’s own defence system. When under attack, plants can release ‘killer’ chemicals that kill off its own tissue along with the attackers, thereby preventing the disease from spreading. Once the emergency is over, antioxidants move in to mop up these chemicals and prevent further tissue damage. The problem with this system, Dr Able says, is that net blotch prefers dead tissue. “That’s why we want to increase the level of antioxidants – to make sure the plant’s defences don’t kill off too much tissue. “The trick is getting the balance just right. You need the plant cell to switch on all its other defence responses. But once you reach a certain stage you don’t want that any more. You want to make sure the antioxidants are there mopping up everything that’s around the place and making sure there’s no more damage to the plant cell.” Antioxidants may have other benefits for the plant too, says Dr Able. “They’re probably also going to give resistance to abiotic stresses like drought and UV light.” The other defences Dr Able and her group have lined up include a mechanism for dealing with fungal toxins and a ‘switch’ to make sure these defences are turned on at the right time and not constantly pumping energy into defence. “If we can combine this antioxidant GENETIC DIVERSITY DICTATES SURVIVAL AND ECONOMICS BY BRAD COLLIS n Plant genetic diversity goes far beyond ensuring graingrowers have access to germplasm offering economic gains – it underpins the survival of the human race, ICARDA-based researcher Dr Ken Street told delegates at the Grains Week conference. “Yes, it’s about the genetic resources that plant breeders need to improve crops, but it is also about global food security and about preserving the environmental services that underpin clean air and water,” he said. Dr Street has been playing a central role in the work of the Global Crop Diversity Trust in the Central Asia and the Caucusus (CAC) region. From his base in Aleppo, Syria, he has been exploring remote regions for modern crops’ ancestors that may provide breeders with genes that can confer traits such as frost and drought tolerance to modern crop varieties. The GRDC and the Australian Government are major supporters of the work. Dr Street addressed the GRDC board during his Grains Week visit. Dr Street explained that while Central Asia was the centre-of-origin for cereals (and for most food grains) there was very little genetic material from this region in Australian wheat genealogy. “The genetic base of Australian wheat is comparatively narrow, coming from a Western European lineage,” he said. “However, Central Asia is the place to look for harsh climate traits like frost and drought tolerance, and resistance to diseases such as stripe and yellow rust.” Dr Street said ICARDA researchers had found resistance to all rusts – leaf, yellow and stripe – in many wild relatives and landraces from Central Asian plant material. But he used Grains Week to ‘up the ante’, warning that time was running out unless the world community committed itself to preserving the collections it already had, as well as increasing efforts to find any remaining genetic resources before even the most remote regions succumbed to the spreading human footprint. Dr Street said genetic diversity was the mechanism that allowed species to evolve and adjust to environmental changes. Global warming was likely to place unprecedented pressure on domesticated plants, such as crops, because of the speed with which the change was happening, he said. Aside from temperature and the impact this will have on plants germinating and flowering, there was also the unknown impact of new or more virulent pests and diseases. “While modern agriculture relies on genetically uniform varieties, a genetically uniform population has less capacity to respond to changes in the environment and is thus more prone to extinction,” Dr Street said. Despite the importance of plant genetic diversity and proper management of existing collections around the world and in Australia, most collections were facing increasing pressure from budget cuts. He said the Global Crop Diversity Trust, established a year ago capacity with some of the other things we’re looking at, this combination is going to be a multi-pronged approach to defence. Rather than deploying one disease resistance after another, if we can get it to throw all of these up at once then it’s going to be much better.” Dr Able says it will be several years before her team will have any outputs to pass on to breeding programs, but she is confident the resistance levels achieved by this approach will be unlike anything seen before. “Using this approach the plant could stay resistant for three or four times as many years as our conventional varieties.” GRDC Research Code CMB00006 More information: Michael McLean, Molecular Plant Breeding CRC, michael.mclean@ molecularplantbreeding.com; Dr Amanda Able, 08 8303 7245, firstname.lastname@example.org Plant breeding/Genetic resources GROUND COVER JUNE -- JULY 2006 26 as an instrument of the International Treaty on Plant Genetic Resources for Food and Agriculture, was trying to raise US$260 million as an endowment fund generating US$12 million a year for conservation – in perpetuity. Australia had already contributed US$15 million, but many of the richer developed countries had yet to respond. He also pointed to the significant economic spin-offs that come from germplasm collections, citing the example of boron tolerance genes collected from the Mediterranean landraces and stored at the Australian Winter Cereals Collection at Tamworth. After back-crossing into a new cultivar in the early 1990s, it has been adding an average of $3 million a year to the value of South Australia’s wheat crop. “Globally, the economic impact of boron tolerance genes is now billions of dollars a year,” he said. There was a similar story behind just about every modern crop variety: “Yet less than 200 kilometres from where I live, billions of dollars are being spent every month effectively destroying a country (Iraq) … and we can’t even raise a comparatively tiny amount to safeguard agriculture.” GRDC Research Code CMB00006 More information: Dr Ken Street, ICARDA, email@example.com Dr Ken Street at Grains Week. PHOTO: BRAD COLLIS A multi-pronged approach to disease defence: Dr Amanda Able.
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