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I was fortunate enough to attend the EFPP/BSPP meeting in Copenhagen and was requested to report back on a session that particularly interested me.
I attended the Population Diversity and Dynamics Session, not least because I was presenting in the morning, but I decided to return in the afternoon for the continuation of the same session. Two talks on yellow (stripe) rust of wheat grabbed my attention in particular, as they reminded me of the continuing importance and global nature of Plant Pathology. Eugene Milus (Univ. of Arkansas) told us how new isolates of Puccinia striiformis f. sp. tritici are causing the most widespread and severe yellow rust epidemic in US history. Before 2000, yellow rust was infrequent in most states but since then has become one of the most important rust diseases in the USA. A quick look at the USDA website reveals that in 2003, a yellow rust epidemic caused wheat yield losses of 2. 4 million tonnes and led to multi-million dollar fungicide application. Dr Milus has shown through AFLP fingerprinting that the new isolates of P. striiformis appear to come from a different genetic background to those isolated pre-2000 and have now become the dominant population. Moreover, the new isolates infect wheat lines previously resistant to the old races and appear to be more aggressive and better adapted to warmer temperatures. These new isolates of P. striiformis have also appeared at the same time on different continents.
The big question is how has this happened? The presentation by Mogens Hovmøller gave some insight into this as he has been studying genetic variability of P. striiformis on field and global scales. He too has found clones of the fungus on different continents in the same year and concludes that rust spores may move across very large distances in a short period of time. This suggests that the new P. striiformis isolates may be a global threat to those not deploying the appropriate resistant wheat varieties. As to the origin of the new isolates, there was some debate. The low AFLP similarity between the old and new isolates sparked a discussion about the possibility of sexual recombination in P. striiformis but there is no evidence as yet to support this.
The yellow rust talks were a good story of contemporary plant pathology and showed the use of both molecular and applied techniques in tackling and understanding the problem. I haven’t had to think much about rust diseases since my undergraduate days but with the prospect of introducing some MSc students to plant pathology very soon, yellow rust might well now appear in a lecture. I’ve also dug out some related references for other new yellow rust enthusiasts.
Steele, K. A. , Humphreys, E. , Wellings, C. R. and Dickinson, M. J. 2001. Plant Pathology 50, 174-180.
Brown J. K. M. , Hovmoller M. S. 2002. Science 297, 537-541.
HovmÃ¸ller M. S. , Justesen A. F. , Brown J. K. M. 2002. Plant Pathology 51, 24-32.
Milus E. A. , Seyran E. , McNew R. 2006. Plant Disease 90, 847-852.
John Clarkson, Warwick-HRI