Segregation for aggressiveness in sexual offspring of the yellow rust pathogen Puccinia striiformis

Recent events in worldwide populations of the fungal pathogen Puccinnia striiformis, which causes the yellow rust disease on wheat and other cereals, have suggested that other factors than shifts in virulence can lead to epidemic events. For instance, the spread of two strains across four continents that has occurred within the last 10-15 years seems to be a result of high temperature adaptation combined with a relatively short latent period (Hovmøller et al. 2008; Milus et al. 2009). Variation for quantitative traits like latent period has often been hypothesized to play a significant role in population shift but only very few experimental data have been generated. Here we report difference for components of aggressiveness which included latent period and lesion growth for 17 isolates derived from a selfing of an aggressive isolate using Berberis vulgaris. A group of offspring isolates had a significantly longer latent period and higher lesion growth than the parental isolate. Interestingly, the two traits were found to be positively correlated where a long latent period was correlated with a higher lesion growth rate. This may suggest a trade-off between latent period and lesion growth. All isolates were assessed on seedlings of two highly susceptible host varieties and the two hosts gave similar results. In a previous study the progeny isolates showed segregation for virulence/avirulence and SSR markers (Rodriguez-Algaba et al. 2014). In conclusion, this study demonstrates genetically inheritable variability for latent period and lesion growth in P. striiformis, even within a single parental isolate. The results contribute to a better understanding of the ability of P. striiformis to adapt to new host varieties and changing environments at the quantitative level.

Chris Sorensen
Aarhus University, Denmark
J. Rodriguez-Algaba, A. F. Justesen and M. S. Hovmøller
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