Virulence and aggressiveness of single-zoospore isolates of Phytophthora fragariae |
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| Authors: | DIANA M KENNEDY JAMES M DUNCAN PATRICIA I DUGARD PAULINE H TOPHAM |
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| Institution: | Scottish Crop Research Institute. Invergowrie, Dundee DD2 5DA, UK;Dundee College of Technology, Bell Street, Dundee, UK |
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| Abstract: | A system for scoring the virulence of isolates of Phytophthora fragariae based on a scale of root rot from 0 ( no symptoms ) to 5 (76-100% roots roiled) on a series of strawberry cultivars is described. Thirty-two single-zoospore isolates from one field site were compared by subjecting their root rot scores to cluster analysis and this grouped them into two major clusters equivalent to physiologic races B66–3 and B66-11, Different sub-clusters of isolates of race B66-11 produced different degrees of rotting on the same hosts. Apart from differences in virulence between the sub-clusters there was some evidence for differences in aggressiveness between isolates within sub-clusters.
Increasing inoculum concentration by over 300-fold increased rotting by c . 25% but did not alter the rankings of different isolate/host combinations. Repeated passage of isolates through cultivars of differing susceptibilities did not affect their pathogenicity. |
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