Abstract
Phenotypic variation (morphological and pathogenic characters), and genetic variability were studied in 50 isolates of seven Plasmopara halstedii (sunflower downy mildew) races 100, 300, 304, 314, 710, 704 and 714. There were significant morphological, aggressiveness, and genetic differences for pathogen isolates. However, there was no relationship between morphology of zoosporangia and sporangiophores and pathogenic and genetic characteristics for the races used in our study. Also, our results provided evidence that no relation between pathogenic traits and multilocus haplotypes may be established in P. halstedii. The hypothesis explaining the absence of relationships among phenotypic and genetic characteristics is discussed.
Highlights
Sunflower downy mildew is caused by Plasmopara halstedii
The results showed that the two forms most observed were oval and round, irrespective of the P. halstedii isolate (Fig. 1)
Pathogenic, morphological and genetic characteristics were identified for 50 P. halstedii isolates of several races based on interactions with sunflower plants
Summary
Sunflower downy mildew is caused by Plasmopara halstedii. It is diploid, homothallic, and can reproduce sexually and asexually. The sexual phase is required to produce over wintering propagules, but during the sunflower growing season from spring to autumn there can be several asexual generations (Tourvieille de Labrouhe et al 2000, Sakr 2014). This Oomycete was originally described by Farlow in 1882 as Peronospora halstedii, the name referring to Halsted, who first collected it on Eupatorium purpureum. New races of P. halstedii were discovered worldwide in the cultivation areas of sunflower (As-Sadi et al 2011, Sakr 2014)
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