P-546 - Phylogenetic Diversity of Peronospora belbahrii, the Pathogen Causing Downy Mildew on Basil in Taiwan

Basil downy mildew, caused by Peronospora belbahrii Thines, is one of the most destructive diseases affecting global basil (Ocimum spp.) production. The pathogen causes yellowing or chlorotic lesions between leaf veins, leading to leaf shrinkage, necrosis, or even complete loss of production. Although the disease has been documented in Taiwan since 2010, knowledge of its reproduction, survival, and population diversity remains limited. The phylogenetic relationships and diversity of 46 P. belbahrii isolates collected from eight locations in central and southern Taiwan, along with reference sequences obtained from the NCBI GenBank were analyzed, aiming to infer the genetic diversity and the mode of reproduction of P. belbahrii in Taiwan. Partial sequences of three housekeeping loci- the ITS region, cytochrome c oxidase subunit II (cox2), and transcription elongation factor 1-α (tef1)- were analyzed, among which the ITS and cox2 loci were more informative than tef1 in differentiating the P. belbahrii population from Taiwan. Based on the concatenated sequences, the P. belbahrii haplotypes from Taiwan and the reference sequences from other countries were clustered into two major clades. Further analysis of nucleotide diversity, haplotype diversity, linkage disequilibrium, and the minimum number of recombination events suggested a certain level of genetic diversity and potential mixed modes of reproduction for the pathogen in Taiwan. This is the first study providing some insights into the genetic diversity of the pathogen in Taiwan, which warrants further studies in the future.