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Main research question/goal
The aim of this research is to stimulate the optimal and sustainable management of chrysanthemum white rust. This disease is caused by Puccinia horiana, a quarantine fungus. Control of this disease is sometimes problematic; answering some remaining questions about this pathogen may help to improve control measures. Are there pathotypes? Is there fungicide resistance? How does the pathogen enter a nursery? Can we determine the number of P. horiana spores in the air and use this data to guide fungicide treatments? How many resistance genes are present in chrysanthemum and how are they inherited? Can we develop markers that are linked to these resistance genes and use them in breeding? Is there international movement of pathogen strains and recombination with local isolates?

Research approach
We first characterize the pathogen population in terms of pathotypes by establishing a worldwide collection of isolates and testing those on a series of differential cultivars. Based on the resulting resistance profiles we determine the minimum number of resistance genes present in chrysanthemum. We assess the inheritance of resistance and AFLP markers in the allohexaploid host using the progeny of a cross. Characterization of the pathogen population in terms of fungicide resistance allows us to determine which crop protection products are still effective. We also characterize the pathogen population genotypically via the development and application of SNP markers. Using air sampling and real-time PCR we determine the (timing of the) airborne spread of the basidiospores. With this information, we aim to determine the entry pathways in a nursery and optimize the timing of fungicide applications.

Chrysanthemum (particularly as cut flowers) is one of the most important ornamental crops worldwide. In Belgium, potted chrysanthemum and especially multiflora chrysanthemum are economically important. Flanders (northern Belgium) also has a number of leading chrysanthemum breeders that are affected by P. horiana’s quarantine status. Chrysanthemum white rust can emerge suddenly and locally on a large scale. Such occurrences can substantially affect yield and quality. To prevent damage from P. horiana, growers spray regularly with fungicides. Some of these fungicides seem to lose their efficacy and European legislation may further reduce the number of available products. A limited number of cultivars are resistant against the fungus, but not always against all strains. The results from our research regarding resistance breeding, guided fungicide treatments and knowledge of the pathogen’s population in terms of race and fungicide resistance are being communicated to the growers, advisors, breeders and scientists via presentations and publications. The information regarding international migration and recombination is communicated to scientists and phytosanitary policymakers.

External partner(s)
Wageningen UR - PRI-Plant Research International
Effective start/end date1/06/0730/06/15

ID: 4146805