LAUSR

Atractylodes lancea Thunb. DC (cangzhu) is a traditional Chinese medicinal plant (Cai et al., 2020). In June 2020, leaf spots were observed in A. lancea plants at the Chongqing Institute of Medicinal Plant Cultivation located in Nanchuan District, Chongqing, China (29°8'26.46″ N, 107°13'23'21″ E). Approximately 75% of the plants displayed leaf spot, partial leaf wilting, and stunted growth, and some plants died. To determine the cause of this disease, five typical leaf spots were cut into small pieces. The pieces were successively surface-disinfected with 0.5% NaClO for 1 min and 75% ethanol for 30 s, washed thrice with sterile water, and placed on potato dextrose agar (PDA) to incubate at 25 ℃. These isolates initially formed abundant white aerial mycelium, then gradually developed a rose pigmentation with a brownish color in the center and grayish rose at the periphery of the colony (Li et al. 2019). Mycelial tips were picked and placed on carnation leaf agar (CLA) and inoculated for 7 days. The macroconidia of the isolates were slender, distinctively curved in the bottom half of the apical cell, and sickle-shaped, with 3-4 septa. They ranged in size from 16.68-26.49 × 1.48-2.34 μm (n=50). The microconidia were fusiform with or without one septum. Their size ranged from 6.19-11.02 × 1.25-1.43 μm (n=50) (Li et al. 2019). The morphological characteristics of the isolates were consistent with those of Fusarium spp. PCR amplification and DNA sequencing of the internal transcribed spacer (ITS) region and β-tubulin (TUB2) gene were performed using the primers ITS1/ITS4 (White et al. 1990) and Bt-2a/Bt-2b (Robideau et al. 2011), respectively. BLASTn analysis revealed that the ITS sequences of the isolates were 100% identical to those of the F. acuminatum isolates from the Fusarium MLST database (http://isolate.fusariumdb.org/guide.php). Further analysis revealed that the TUB2 sequences were 99.14% identical to those of the F. acuminatum strain S16 isolates (MF662644) from the GeneBank database of the NCBI server. Based on the morphology and sequence analyses, the isolates were identified as F. acuminatum. Pathogenicity tests were conducted on 1.5-year-old A. lancea plants by inoculating spore suspensions under greenhouse conditions (25°C). For this, wound were made on leaves by piercing with sterilized toothpicks. 30 μl of spore suspension containing 2 × 106 conidia/ml was placed on each wound. Wounds on the leaves of control plants were inoculated with 10 μl of sterile distilled water. There were three plants for each treatment. After incubation at 25 °C for 5 days in a greenhouse, the leaves of the treated plants all showed partial wilting, consistent with the field observations. No symptoms were observed in controlled plants. The fungi were again isolated from the symptomatic tissues and were identical to the original isolate. The experiment was repeated twice with similar results. Pathogenicity symptoms were similar to what was first observed in the field and the isolated fungi were verified based on morphological characteristics, thus fulfilling Koch's postulate. To the best of our knowledge, this is the first time that A. lancea leaf spot caused by F. acuminatum has been discovered in China. The leaf spot caused by F. acuminatum on A. lancea has serious yield loss, and proper control measures should be applied.