First Report of Powdery Mildew Caused by Podosphaera xanthii on the Invasive Verbena brasiliensis in Texas
First Report of Powdery Mildew Caused by Podosphaera xanthii on the Invasive Verbena brasiliensis in Texas
复制标题
德克萨斯州入侵巴西马鞭草上首次报道由黄豆球菌 (Podosphaera xanthii) 引起的白粉病
DOI：
10.1094/pdis-01-20-0022-pdn
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发表时间：
2021
期刊：
影响因子：
4.5
通讯作者：
Crawford, K. M.
中科院分区：
文献类型：
--
作者：
Luecke, N. C.;Adams, T.;Crawford, K. M.
巴西马鞭草（Verbena brasiliensis，唇形科）是一种高度入侵的植物，在美国南部发现。正如它的名字所暗示的那样，它起源于南美洲，但由于其高度的杂草生长模式和耐受干旱和干扰的能力而在美国蓬勃发展。在2019年夏天，64株巴西葡萄植物在休斯顿大学的温控温室（德克萨斯州休斯顿）中生长。8株植株的茎和叶的近轴面表现出白粉病感染的症状。在叶片上观察到白色圆形粉末状菌落，具有大量空中散布的孢子，似乎与叶龄无关。经检查，在感染区域检测到叶片组织的失绿。分生孢子梗（n= 25）平均长度为210 µm，并在真正的链中产生6至9个分生孢子。分生孢子梗的基细胞从菌丝上分支，形成直角，基部平均长35 µm。分生孢子透明，卵形，大小为28 - 31× 19 - 21 µm。这些结构是Podosphaera属的白粉病菌的典型无性型。在菌落内未观察到裂殖吸虫。形态特征和测量结果与黄单囊壳（Podosphaera xanthii）（Braun and Takamatsu 2000）一致。通过将有症状的巴西葡萄叶轻轻摩擦到巴西葡萄植物的健康叶上来证实致病性（Lee 2013）。接种15株植物，5株未接种作为阴性对照。接种的植株在6至12天（平均10天）之间出现白粉病症状，而所有对照保持无病。使用ITS 1f和ITS 4引物扩增内转录区（白色等人，1990）。使用NCBI BLAST对三个样品（一个来自原始植物、接种物和再分离的真菌）进行测序和鉴定，并将所得序列保存在GenBank中（MN 818562，[接种物]、MN 818563 [再分离]和MN 818564 [原始]）。所有三个序列与韩国报道的巴西马鞭草上的P. xanthii具有98.7%的相似性（登录号KJ 472787）（Cho等人，2014）。使用Brewer et al.（2011年）。基于用于MAT 1 -1-1和MAT 1 -2-1的阳性和阴性对照，确定所有三份样品均为MAT 1 -1-1。阳性对照包括来自MAT 1 -1-1和MAT 1 -2-1的确认分离株的DNA，阴性对照为无菌水。P. xanthii是一种常见的白粉病物种，已在大范围的重要农业宿主，特别是葫芦上报道（McCreight 2006）。这是在德克萨斯州的第一份正式报告，也是在美国的第一份关于巴西马鞭草的报告。虽然我们没有明确地测量病原体对宿主适合度的影响，但感染可能导致植物入侵能力的降低。由于得克萨斯州是葫芦科作物的大生产国，这种病原体可能会影响该州的农业。鉴于巴西葡萄在高干扰地区（如农田和恢复的草原）的入侵性质，这一发现对农业和本地物种的生态保护具有广泛的重要性。
Brazilian verbena (Verbena brasiliensis, family Lamiaceae) is a highly invasive plant found throughout the southern portion of the United States. As suggested by its name, it originates in South America but has prospered in the United States due to its highly ruderal growing pattern and its ability to tolerate drought and disturbance. During the summer of 2019, 64 V. brasiliensis plants were growing in the University of Houston, s temperature-controlled greenhouse (Houston, TX). Eight plants exhibited symptoms of powdery mildew infection on the stems and adaxial surface of the leaves. White circular powdery colonies with high numbers of aerially dispersing spores were observed on leaves, seemingly uncorrelated with leaf age. Upon examination, chlorosis of leaf tissue was detected in areas of infection. Conidiophores (n= 25) were on average 210 µm in length and produced six to nine conidia in true chains. Base cells of conidiophores branched from hyphae forming right angles and averaged 35 µm long at the base. Conidia were hyaline, ovate, and measured 28 to 31× 19 to 21 µm. These structures are typical of the powdery mildew oidium anamorph of the genus Podosphaera. No chasmothecia were observed within colonies. The morphological characteristics and measurements were consistent with those of Podosphaera xanthii (Braun and Takamatsu 2000). Pathogenicity was confirmed by gently rubbing symptomatic V. brasiliensis leaves onto healthy leaves of V. brasiliensis plants (Lee 2013). Fifteen plants were inoculated, and five remained uninoculated to serve as negative controls. Inoculated plants developed powdery mildew symptoms between 6 and 12 days (averaging 10 days), whereas all controls remained disease-free.DNA was extracted from fungal tissue from the original plant, inoculum sample, and the newly infected leaves. The internal transcribed region was amplified using the ITS1f and ITS4 primers (White et al. 1990). Three samples (one from the original plant, the inoculum, and the reisolated fungi) were sequenced and identified using NCBI BLAST, and the resulting sequences were deposited in GenBank (MN818562,[inoculum], MN818563 [reisolate], and MN818564 [original]). All three sequences had 98.7% similarity to the P. xanthii on Brazilian verbena reported in South Korea (accession no. KJ472787)(Cho et al. 2014). All three samples were amplified using the mating-type primer sets and PCR protocol described in Brewer et al.(2011). All three samples were determined to be MAT1-1-1 based on positive and negative control used for MAT1-1-1 and MAT1-2-1. Positive controls included DNA from confirmed isolates from MAT1-1-1 and MAT1-2-1, and negative controls were sterile water. P. xanthii, a common powdery mildew species, has been reported on a large range of important agricultural hosts, especially cucurbits (McCreight 2006). This is the first formal report of P. xanthii in Texas as well as the first report on Brazilian verbena in the United States. Although we did not explicitly measure the pathogen, s effect on host fitness, infection may result in a reduction in the plant, s invasiveness. Because Texas is a large producer of cucurbits, this pathogen could impact agriculture in the state. Given the invasive nature of V. brasiliensis in areas of high disturbance, such as agricultural fields and restored prairies, this discovery has broad importance for both agriculture and the ecological conservation of native species.