Occurrence Of Powdery Mildew Caused By PodosphaeraXanthii On Verbena Bonariensis
In-Young Choi*, Joon-Ho Choi1, Lamiya Abasova1, and Hyeon-Dong Shin1, 2
1Department of Agricultural Biology, Jeonbuk National University, Jeonju 54896, Korea
2Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Korea
Verbena bonariensis (Verbenaceae), known as purple-top vervain or Argentinian vervain, is a perennial, herbaceous plant native to tropical South America. It is widely grown as an ornamental plant worldwide. During summer and autumn of 2022, V. bonariensis of an unknown cultivar with purple-violet flowers was found infected by powdery mildew fungus with 100% disease incidence in a public garden in Jeonju, Korea. White, superficial mycelia developed on infected plants and subsequently covered whole surfaces of leaves and stems, resulting in leaf discoloration and early defoliation. High disease severity caused poor growth of the plants, resulting in premature senescence and reduced flowering. No chasmothecia were observed throughout the growing season. Diagnostic structures of asexual mprphs were consistent with those of Podosphaera xanthii. Thus, based on morphology and molecular analysis on the internal transcribed spacer regions and large subunit gene of the rDNA, the isolate on V. bonariensis in Korea was identified as P. xanthii. Hitherto, powdery mildew of Verbena spp. associated with Podosphaera sp. (including Sphaerotheca sp.) has been globally reported. P. xanthii on V. bonariensis was recorded from China and Japan, while in Korea, it was recorded on Verbena brasiliensis, but not on V. bonariensis. To our knowledge, this is the first report of powdery mildew disease caused by P. xanthii on V. bonariensis in Korea. Our field observations suggest that this powdery mildew occurs on V. bonariensis planted in the shade. This finding could be useful for the breeding program of Verbena spp. and for planting strategies in gardens.