First report of powdery mildew caused by Erysiphe euonymicola on wintercreeper (Euonymus fortunei) in China.

Abstract

Wintercreeper (Euonymus fortunei) is an evergreen shrub, a semi climbing plants with very strong vitality. It can tolerate a broad range of environmental conditions varying from full sun to deep shade. So, wintercreeper is a good groundcover plants and tree species of vertical greening. It is widely used in urban greening in China. In May 2021, severe powdery mildew signs were found on wintercreeper plant in a garden of Luohe cities of Henan province, China. Approximately 40% of leaves on a plant were symptomatic, and about 60% of the plants were infected. Powdery mildew colonies appeared as white spots on the upper surface of the leaf and stem of the plants in the initial stage. Later, mycelial growth was amphigenous, thick, forming irregular white patches, effused to cover the entire leaf surface. At last, leaves turned yellow and senescence. One representative voucher specimen was deposited at the herbarium of Shangqiu Normal University (SQNU), Shangqiu, China, under the accession number of EF02. Conidiophores arising terminally from the mother cell, mostly central, erect, straight, 40.7 to 67.7µm (average 49.1µm) 6.1 to 8.5µm (average 7.5µm) (n=30) composed of 3 to 4 cells and produced conidia singly. Conidia were obovoid-ellipsoid, apex rounded, base subtruncate, ends truncate or subtruncate, long 26.1 to 36.4µm (average 30.7µm) and width 9.9 to 16.0µm (average 11.8µm) (n=30). No chasmothecia were observed. The morphological characteristics and measurements were consistent with those of Erysiphe euonymicola (Braun and Cook 2012). The internal transcribed spacer regions of EF02 were amplified using primers ITS1/ITS4, and sequences directly. The obtained sequence of 648 bp was deposited in GenBank (accession no. OM304857). The isolate (EF02) was 99.83% similarity with E. euonymicola on E. fortunei var. radicans (KM361621 from Korea) (Lee et al. 2015), 99.23% with E. euonymicola on E. fortunei (MT510003 from USA), 99.23% with E. euonymicola on E. japonicus (LC270841and LC270834 from Azerbaijan, AB250228 from Japan ). The domains D1 and D2 of the 28S rDNA obtained 619 bp sequences from the powdery mildew of isolate EF02 with primer NL1/NL4, deposited in GenBank (OM302187). A NCBI BLAST search of the EF02 isolate showed 100% similarity with 28S rDNA sequence of E. euonymicola on E. japonicus (AB250230 from Japan) (Limkaisang et al. 2006), and 28S phylogenetic tree analysis EF02 isolate is located in the same branch as E. euonymicola. The pathogenicity was confirmed by gently pressing the infected leaves onto five healthy plants. Five uninoculated plants served as controls. Ten inoculated and non-inoculated plants were placed in different growth chambers with 14-h photoperiod at 22±2°C and 60% of relative humidity. After 11 to 13 days, powdery mildew colonies developed on inoculated plants. Non-inoculated control plants did not show powdery mildew symptoms. The fungus on inoculated leaves was morphologically identical to that first observed in the field. Although E. euonymi-japonici (synonym E. euonymicola) has been recorded on E. japonicus in China (Li et al. 2011), this is the first report of powdery mildew caused by E. euonymicola on E. fortunei in China. It could become a threat to the widespread planting of wintercreeper, Similar report has been in Korea (Lee, C. K., et al. 2015).