Catalpabungei起源于中国。它生长迅速,并具有垂直对齐的树干,使其成为值得称赞的建筑材料和重要的经济物种。2022年7月,南阳兰湖农场(调查面积约700亩)发生严重叶斑病(北纬33°3\'23\",112°28'50''E),河南省,中国。叶片病的病发率到达54%(n=100)。该病最初表现为不规则的圆形斑点,呈黄棕色,随后向各个方向延伸。稍后,病变周边表现出变暗效应,导致泛黄。随机收集20片患病的叶子,并在感染组织和健康组织之间的界面处切成小块。将组织在75%乙醇和1%NaClO的溶液中灭菌30秒和1分钟,分别。在无菌水中冲洗后,将这些片置于马铃薯葡萄糖琼脂(PDA)板上并在25°C下孵育5天。共获得29株纯化真菌,在形态特征方面表现出可比的表型。分离三个菌株(QS1-1、QS1-2和QS1-3)用于后续研究。菌落表现出丰富的气生菌丝体,背面的色调从深绿色到灰褐色。分析分生孢子的形态特征,马铃薯胡萝卜琼脂(PCA)用作培养基,并在25°C下以12小时的亮/暗循环孵育。分生孢子呈球形或球形,深棕色,有3到5个横向隔片,和1至4个纵向隔片,测量12.4至36.7×4.4至9.0μm(n=100),锥形喙的长度范围从0到4.3μm。这些形态特征表明该病原体与链格孢属物种具有相似性。rDNA内部转录间隔区(ITS),翻译延伸因子1-α基因(tef1),甘油醛3-磷酸脱氢酶基因(gapdh),和RNA聚合酶II第二大亚基(rpb2)被扩增用于进一步的分子鉴定。将得到的序列提交给GenBank,登录号如下:OR733559,OR742124,OR761873(ITS),OR939796,OR939797,OR939798(tef1),OR939801,OR939802,OR939803(gapdh),和PP054846、PP054847、PP054848(rpb2)。由组合基因(ITS,tef1,gapdh,和rpb2)的序列,通过邻居连接方法与类型菌株的序列并列。这三个菌株在系统发育树中与链格孢菌CBS121456菌株形成了进化枝,与其他链格孢属物种分离。形态学特征和分子分析支持该菌株是链格孢菌的成员(Woudenberg等人。2015).为了验证致病性,将所有三个菌株的分生孢子悬浮液(106分生孢子ml-1)接种到五个幼苗的三个健康叶片上,用棉球吸收50μl接种物。另一组五株植物接受无菌水作为对照。将所有植物在28°C和90%相对湿度的气候室中孵育。接种后四天,观察到类似自然现象的病变,而对照植物没有症状。随后的再分离产生的培养物在形态和分子上与原始菌株相同,履行科赫的假设。在中国已经报道了由烟草疫霉引起的C.bungei茎溃疡(Chang等人。2022年)。这是中国首例有关A.alternata引起C.bungei叶斑的报道。需要对控制这种疾病的管理选择进行进一步研究,并且仍需要明确宿主范围以进行准确的疾病管理。
Catalpa bungei originates from
China. It is fast-growing and possesses a vertically aligned trunk, rendering it a commendable construction material and a significant economic species. In July 2022, a serious leaf spot occurred in the LanLake farm (surveyed area of about 700 acres) in Nanyang (33°3\'23\" N, 112°28\'50\" E), Henan Province,
China. The incidence rate of leaf disease reached 54% (n=100). The disease initially manifested as irregular round spots with a yellowish-brown hue, subsequently extending in all directions. Later, the lesion periphery exhibited a darkening effect, leading to yellowing. Twenty diseased leaves were randomly collected and cut into small pieces at the interfaces between infected and healthy tissues. The tissues were sterilized in a solution of 75% ethanol and 1% NaClO for 30 seconds and 1 minute, respectively. After rinsing in sterile water, the pieces were placed on potato dextrose agar (PDA) plates and incubated at 25°C for 5 days. A total of 29 purified fungal strains were acquired, exhibiting comparable phenotypes in terms of morphological characteristics. Three strains (QS1-1, QS1-2, and QS1-3) were isolated for subsequent investigations. The colony exhibited abundant aerial mycelium with shades ranging from dark green to grey-brown on the reverse side. To analyze the morphological characteristics of conidia, potato carrot agar (PCA) was used as the culture medium and incubated at 25°C with a 12-hour light/dark cycle. Conidia were obclavate or spheroidal, dark brown, with 3 to 5 transverse septa, and 1 to 4 longitudinal septa, measuring 12.4 to 36.7 × 4.4 to 9.0 μm (n=100), with conical beak lengths ranging from 0 to 4.3 μm. These morphological traits suggested that the pathogen shares similarities with the Alternaria species. The rDNA internal transcribed spacer (ITS), translation elongation factor 1-alpha gene (tef1), glyceraldehyde 3-phosphate dehydrogenase gene (gapdh), and RNA polymerase II second largest subunit (rpb2) were amplified for further molecular identification. The resultant sequences were submitted to GenBank with the following accession numbers: OR733559, OR742124, OR761873 (ITS), OR939796, OR939797, OR939798 (tef1), OR939801, OR939802, OR939803 (gapdh), and PP054846, PP054847, PP054848 (rpb2). A Phylogenetic tree was constructed of combined genes (ITS, tef1, gapdh, and rpb2) of sequences, alongside the sequences of the type strains by the neighbor-joining method. The three strains formed a clade with the strains CBS 121456 of Alternaria alternata in phylogenetic trees, being separated from other Alternaria spp. The morphological features and molecular analyses supported the strains as members of Alternaria alternata (Woudenberg et al. 2015). To validate pathogenicity, a conidial suspension (106 conidia ml-1) of all three strains was inoculated onto three healthy leaves of five seedlings, with 50 μl of inoculum absorbed with cotton balls. Another group of five plants received sterile water as a control. All plants were incubated in a climate chamber at 28°C and 90% relative humidity. Four days post-inoculation, lesions resembling natural phenomena were observed, whereas control plants showed no symptoms. Subsequent reisolation produced cultures that were morphologically and molecularly identical to the original strains, fulfilling Koch\'s postulates. Stem canker of C. bungei caused by Phytophthora nicotianae has been reported in
China (Chang et al. 2022). This is the first report of A. alternata causing leaf spots on C. bungei in
China. Further research is required on management options to control this disease and the host range still needs to be clarified for accurate disease management.