First report of Podosphaera fusca Causing Powdery Mildew on Coreopsis lanceolata in China.

Abstract

Coreopsis lanceolata, known as lance-leaf coreopsis, is a perennial plant with high ornamental value. It is widely grown in many public parks and home gardens in China due to its showy flowers. From May to June 2020, typical powdery mildew-signs and symptoms were seen on leaves of C. lanceolata cultivated in the east campus of Henan Normal University, Henan Province, China. Abundant white powder-like masses in spot- or coalesced-lesions were on ad- and abaxial surfaces of plant leaves and covered up to 50 % of the leaf area. The infected leaves were deformed and eventually prematurely senescent. Approximately 80 % of observed C. lanceolata plants showed these signs and symptoms. Unbranched conidiophores (n = 25) were 90 to 200 × 12 to 20 μm and showed a foot cell, followed by 1 to 3 short cells and conidia. Ellipsoid-ovoid shaped conidia (n = 30) were 22 to 36 × 15 to 23 μm, with a length/width ratio of 1.4 to 2.4. No chasmothecia were detected. The powdery mildew fungus was initially identified as Podosphaera fusca based on the morphological characteristics. Total genomic DNA of the pathogen was extracted and the rDNA internal transcribed spacer (ITS) region was amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990; Zhu et al. 2019). The obtained sequence was deposited into GenBank under Accession No. MT899186 and was 100 % identical to P. fusca (JX546297) from Herba eupatorii (Ding et al. 2013). To perform pathogenicity assays, leaf surface of three healthy plants was inoculated with fungal conidia according to a previously described method (Zhu et al. 2021). As a control, three non-inoculated plants were used. The control and inoculated plants were placed separately in two growth chambers (light/dark, 16 h/8 h; humidity, 65 %; temperature, 20 ℃). Fourteen- to sixteen-days post inoculation, powdery mildew signs were noticed on inoculated plants, whereas control remained asymptomatic. Similar results were found by performing two repeated pathogenicity assays. Therefore, based on the morphological and molecular analysis, the pathogen was identified and confirmed as P. fusca. This fungus has been reported on C. lanceolata in Korea (Park et al. 2010) and Italy (Garibaldi et al. 2007). This is, to the best of our knowledge, the first report of P. fusca on C. lanceolata in China. The sudden occurrence of this powdery mildew disease on C. lanceolata may adversely affect the health of valuable ornamentals in China. The precise identification of the causal agent of this powdery mildew of C. lanceolata is a preliminary step in developing effective disease management strategies.