BidenspilosaL.,一年生草本植物,分布广泛,具有新颖的药用特性。2021年1月,深圳路边地区的白粉病发生白粉病疫情,广东省,中国,60-80%的发病率。最初的症状表现为小,不规则白色粉状斑块,主要在叶子的正面。随后,殖民地扩大了,形成遍布叶子的聚积菌落,叶柄,和茎,最终导致叶子的扭曲和衰老。菌丝是透明的,弯曲到笔直,隔膜,具有薄壁和宽度范围从2到8μm。菌丝是乳头状的。Conidopores直立或略微弯曲,长度为80至150µm,宽度为12至18µm(n=30)。通常,这些分生孢子带有2到5个未成熟分生孢子的链,显示正弦轮廓。脚细胞,位于conidophores的底部,是圆柱形和直立的,长度约为33至100µm,宽度约为6至10µm(n=30)。分生孢子是透明的,椭圆形卵形到桶形,缺乏纤维蛋白体。初级分生孢子呈椭球-卵形,以圆形的先端和近截形的基部为特征,宽度为25至40µm×15至22µm。次级分生孢子呈桶状,末端截断或亚截断,宽度为27至35µm×15至20µm。胚芽管表现出经度模式,并在分生孢子的门周或根尖区域显着产生。在收集的样品中未观察到chasmothecia。为了进行分子水平的鉴定,菌丝体和分生孢子从B.pilosa叶收集。随后从这些样品中提取基因组DNA。内部转录间隔区(ITS),使用引物对ITS1/ITS4,IGS-12a/NS1R,和tub2(Carbone和Kohn1999;Scholin等人。1994;怀特等人。,1990).568-bp的ITS,366-bp的IGS,和354bp的tub2序列(GenBank登录号获得OR647592、OR978282和OR978283)。ITS序列显示出超过99.6%的相似性。IGS序列显示出与安布氏杆菌(MK383490)和安布氏杆菌(OK349420)100%的相似性。tub2序列显示出100%的相似性与甘草(MW981257)和甘草(MW981256)。IGS的系统发育分析,ITS和tub2还将获得的序列归入了Ambrosiae复合物中。在形态特征和序列同一性分析的基础上,该病原体被鉴定为安布氏杆菌。为了满足科赫的假设,被感染的叶子被小心地压在六株健康的幼小B.pilosa植物的叶子上,每个都生长在一个单独的罐子里。此外,对照组由六株未接种的植物组成。将所有植物置于温室中:25°C,14/10-h亮/暗光周期,相对湿度50%。10天后,接种的叶子表现出与原始感染植物相似的白粉病菌落。16天,接种的叶片表现出变色和过早的落叶。致病性试验进行了两次。显微镜观察和测序证实分离的真菌与原始病原体相同。先前已在福州的B.pilosa上记录了G.ambrosiae,福建省,中国(Mukhtar等人。,2022年)。然而,据我们所知,这项研究代表了深圳首例由银杏白粉病引起的白粉病。广东省,中国。
Bidens pilosa L., an annual herbaceous plant with a wide distribution, possesses novel medicinal properties. In January 2021, a powdery mildew disease outbreak was documented on B. pilosa plants located in the roadside areas in Shenzhen, Guangdong Province, China, with 60 to 80% disease incidence. Initial symptoms manifested as small, irregular white powdery patches, primarily on the adaxial surfaces of leaves. Subsequently, the colonies expanded, forming coalescent colonies that spread across the leaves, petioles, and stems, eventually leading to the distortion and senescence of leaves. Hyphae are hyaline, flexuous to straight, septate, with thin walls and a width ranging from 2 to 8 μm. Hyphal appressoria are nipple-shaped. Conidophores are erect or slightly flexuous, ranging from 80 to 150 µm in length and 12 to 18 µm in width (n = 30). Typically, these conidophores bear chains of 2 to 5 immature conidia, displaying a sinuate outline. Foot-cells, located at the base of conidophores, are cylindrical and erect, approximately 33 to 100 µm in length and 6 to 10 µm in width (n = 30). Conidia are hyaline, ellipsoid-ovoid to barrel-shaped, and lack fibrosin bodies. Primary conidia are ellipsoid-ovoid in shape, characterized by a rounded apex and a subtruncate base, 25 to 40 µm × 15 to 22 µm in width. Secondary conidia are barrel-shaped with truncate or subtruncate ends, 27 to 35 µm × 15 to 20 µm in width. Germ tubes exhibit a longitubus pattern and are prominently produced at the perihilar or apical region of the conidia. No chasmothecia were observed in the collected samples. In order to conduct a molecular-level identification, mycelium and conidia were collected from B. pilosa leaves. Genomic DNA was subsequently extracted from these samples. The internal transcribed spacer (ITS), intergenic spacer (IGS) and beta-tubulin (tub2) sequences were performed using primer pairs ITS1/ITS4, IGS-12a/NS1R, and tub2, respectively (Carbone and Kohn 1999; Scholin et al. 1994; White et al.,1990). A 568-bp ITS, a 366-bp IGS, and a 354-bp tub2 sequences (GenBank accession nos. OR647592, OR978282 and OR978283) were obtained. The ITS sequence exhibited over 99.6% similarity to Golovinomyces ambrosiae (MT929773) and G. cichoracearum (MH590731). The IGS sequence displayed 100% similarity to G. ambrosiae (MK383490) and G. ambrosiae (OK349420). The tub2 sequence displayed 100% similarity to G. ambrosiae (MW981257) and G. ambrosiae (MW981256). Phylogenetic analysis of IGS, ITS and tub2 also grouped obtained sequences within the G. ambrosiae complex. Based on the analysis of morphological characteristics and sequence identity, the pathogen was identified as G. ambrosiae. In order to satisfy Koch\'s postulates, an infected leaf was carefully pressed onto leaves of six healthy young B. pilosa plants, each grown in a separate pot. Additionally, a control group consisted of six non-inoculated plants. All plants were placed in a greenhouse: 25°C, 14/10-h light/dark photoperiod, and relative humidity 50%. After 10 days, the inoculated leaves exhibited powdery mildew colonies similar to those observed in the original infected plants. At 16 days, the inoculated leaves exhibited discoloration and premature leaf drop. The pathogenicity test was conducted twice. Microscopic observation and sequencing confirmed that isolated fungus was identical to the original pathogen. G. ambrosiae has previously been documented on B. pilosa in Fuzhou, Fujian Province, China (Mukhtar et al., 2022). However, to the best of our knowledge, this study represents the first report of powdery mildew caused by G. ambrosiae on B. pilosa in Shenzhen, Guangdong Province, China.