Ground Cover Supplement : GC Supplement - Root and crown diseases
PLANT BREEDING In a study funded by the GRDC, PhD scholar Cassandra Percy, working with Associate Professor Mark Sutherland, has demonstrated that the pathogen has two modes of growth. In glasshouse and field trials she studied the spread of the Fusarium fungus in seedlings and adult plants that differ in their resistance to crown rot. Ms Percy observed that while the pathogen spreads between tillers and higher up the stems as the plant approaches maturity, this movement is much slower in the green tissue of resistant wheats compared to susceptible wheats. However, at crop maturity the fungus appears to switch to saprophytic growth on the dead mature straw, resulting in rapid colonisation of the upper nodes of the tillers (but not the heads) around the time of harvest. This is seen in both susceptible and resistant lines and may explain why growing partially resistant wheats such as Sunco does not necessarily reduce the inoculum level for the following season. In a separate study, a selection of partially resistant host genotypes was challenged with a range of crown rot isolates gathered from across Australia by Ms Bentley. While fungal isolates differed significantly in their aggressiveness, the growth of all isolates was partially inhibited in a consistent manner on all resistant wheats when compared with susceptible wheats. These observations suggest there is no pathogenic race structure in the fungus and that sources of crown rot resistance are likely to be stable and effective across Australia. Further work is required to verify these observations. GRDC Research Codes GRS81, USQ8 More information: Alison Bentley, 02 9351 2861, email@example.com; Associate Professor Mark Sutherland, 07 4361 2360, firstname.lastname@example.org More resistance for durum ALL COMMERCIAL DURUM wheat varieties are very susceptible to crown rot, but Dr Hugh Wallwork, of the South Australian Research and Development Institute (SARDI), reports that each year data indicate that KalkaA is slightly less susceptible than Tamaroi or Yallaroi. With colleagues in SA, NSW and Queensland, Dr Wallwork is leading the program to develop durum varieties with improved crown rot resistance. The SA-based program is taking three different approaches to improving resistance. In one, they are using two wild relatives of Triticum dicoccon that have consistently shown higher resistance in the glasshouse and in mini-pot trials. In 2006, some of the derived lines had their first year of field-testing. The severe drought made accurate assessments difficult, but two lines have shown some promise and will be subject to further development, genetic analysis and field testing. In a second approach, they are assessing lines developed by the durum breeder Dr Tony Rathjen that are derived from crosses between bread wheat and durum. A third avenue is using molecular markers to transfer the resistance from KukriA bread wheat to durum variety KalkaA. Meanwhile, PhD student Friederike Eberhard is testing the effectiveness of markers to track the transfer of crown rot resistance genes from northern region bread wheats to durums. In parallel work, Dr Ray Hare, from the NSW Department of Primary Industries, is using a program of crossing to transfer the resistance of the previously characterised wheat lines into durum lines. Field- testing of these bread wheat x durum crosses is being conducted by Dr Steven Simpfendorfer. GRDC Research Code DAS00073 More information: Dr Hugh Wallwork, 08 8303 9382, Wallwork.Hugh@saugov.sa.gov.au Dr Hugh Wallwork is leading an extensive breeding program to improve durum's crown rot resistance. All commercial durum varieties are susceptible. – 2-49, W21MMT70 and IRN497 – as well as in the variety Sunco. The genomic regions identified in each of these lines are largely different, and represent opportunities for pyramiding (or combining) these genes to provide new lines with improved resistance. Markers for the resistance in the line 2-49 are being field-trialled in Mexico and Turkey by the International Maize and Wheat Improvement Center (CIMMYT), and early reports suggest they are effective in selecting resistant plants in those environments. Crosses between different sources of resistance are well advanced and are being tested in conjunction with Dr Graham Wildermuth and Dr Damian Herde at the Queensland Department of Primary Industries and Fisheries’ Leslie Research Centre in Toowoomba. Recently, crown rot has been recognised as a more significant constraint on barley production than previously thought. Dr Anke Lehmensiek, a University of Southern Queensland postdoctoral fellow funded by the GRDC, has identified markers for resistance to crown rot in a population produced from a cross between the susceptible barley cultivar Tallon and Hordeum spontaneum, a close relative of barley that has significant resistance. Lines from this population are now being backcrossed with commercial materials. GRDC Research Codes USQ00007 and USQ00008 More information: Associate Professor Mark Sutherland, 07 4361 2360, email@example.com 15 ROOT & CROWN DISEASES GROUND COVER PHOTO: EMMA LEONARD The biology of crown rot fungus is under the microscope, revealing why inoculum levels may increase even under resistant varieties.
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