First Report of Daylily Leaf Streak Caused by Kabatiella microsticta in China

摘要

cultivated for its flowers. Daylily is sold in Asian markets as fresh or dried flowers (the flowers of some species, e.g., Hemerocallis citrina, are edible) or as the corm, which is used for medicinal purposes. In June 2011, daylily leaf streak was found in a nursery of Jilin Agricultural University, Jilin Province, China. Symptoms included water-soaked, irregular spots along the leaf midvein that turned orange to reddish brown and eventually enlarged to coalesce into extensive, necrotic streaks along the length of the leaf, as previously reported (2). Heavily infected leaves often withered and died. Four isolates were recovered from necrotic tissue of leaf spots and cultured on potato dextrose agar (PDA) at 25°C. All colonies were initially cream to peach colored and appeared slimy. With the maturation of the culture, the colonies became dark brown to black with sparse aerial hyphae. Blastic conidia formed simultaneously on intercalary or terminal, undifferentiated conidiogenous cells, and were scattered in dense sections on culture surface. When the conidia dropped from conidiogenous cell, an indistinct scar or a denticle remained. Conidia were hyaline, one-celled, smooth, ellipsoidal, and variable in size (2.73 to 6.01 × 8.45 to 19.36 μm), and all morphological characteristics were consistent with Kabatiella microsticta Bubak (syn. Aureobasidium microstictum; 2,4). The internal transcribed spacer (ITS) region of the nuclear rDNA was amplified using primers ITS4/ITS5 (1). ITS (534 bp) was identical among all four isolates (GenBank Accession No. HE798117) and 100% identical to that of K. microsticta CBS 114.64 (FJ150873). Pathogenicity was confirmed by spraying 20 seedlings of daylily, propagated in tissue-culture medium, with a conidial suspension (106 conidia/ml) of each isolate. A second set of 20 seedlings was sprayed with the same volume of sterile water as the noninoculated control treatment. Plants were grown in the greenhouse at 20 to 25°C and were covered with plastic bags to maintain humidity on the foliage for 72 h. After 5 days, the foliar symptoms described earlier for the field plants appeared on the leaves, whereas the control plants remained healthy. K. microsticta was reisolated from the leaf spots of all 20 inoculated plants. Leaf streak is the most destructive disease of daylily, and was previously reported in Japan and the United States (Illinois, Kentucky, Mississippi, Louisiana, Pennsylvania, Maryland, Virginia, Florida, North Carolina, and Georgia) (3). To our knowledge, this is the first report of the disease caused by K. microsticta in China.