太子参是我国最常见、最珍贵的中药材之一,具有多种药理作用,主要产于中国西南部和东南部的贵州和福建省的酸性土壤中,分别(Wu等人。2020)。然而,假丝酵母的连续单一栽培会导致严重的根腐病,地下块茎的生物量和质量下降。假丝酵母的块茎通常在12月种植并在明年6月收获。根腐病通常在5月开始发展。在石兵县连续的单一栽培田下,假太子参的根部和基茎中根腐病的发病率在37%至46%之间。贵州省,中国(东经108°12,27°03N)(李等人。2017)。2018年5月在施宾县观察到严重的根腐病。感染的植物显示卷曲,枯萎,和黄色的叶子,枯萎病,生长迟缓,根腐病,和产量损失。在根部和周围土壤上观察到丰富的白色菌丝体。两个真菌分离物,命名为GZ20190123和GZ20190124,是从马铃薯葡萄糖琼脂(PDA)上培养的有症状的根获得的。两个分离株生长的最佳温度范围为25至30°C。GZ20190123生长的最佳pH范围为5至5.5,而GZ20190124在pH5至8.5之间生长更好。GZ20190123和GZ20190124在30°C下的平均菌丝生长速率分别为2.1和1.5厘米/天,分别。两个分离物的分生孢子为卵形或扁桃体,并以单链或支链产生。用引物ITS1和ITS4扩增内部转录间隔区(ITS)区(White等人。1990).序列作为登录号存放在GenBank中。用于GZ20190123的MN726736和用于GZ20190124的MN726738。序列比较显示,与先前报道的MucorracecosusBull分离株xsd08071具有99%(GZ20190123)和97%(GZ20190124)的同一性。(登录号。FJ582639.1),并分离出脆弱的MucorBainier的BM3(登录号MK910058.1),分别,系统发育分析证实了这一点。测试了这两个分离株对假赤霉病菌的致病性。用75%乙醇对假丝酵母的六个根进行表面灭菌,并使用无菌牙签对每种分离物进行菌丝体接种。将无菌蒸馏水刺入12根作为对照。处理过的根在温室中孵育16小时日长[光强度146.5μmol/(m2·s)]和日/夜温度26°C/18°C。接种后7天,接种的根和芽上显示出预期的症状,而有豆芽的对照根没有任何症状。从患病的根中重新分离出真菌,并根据ITS序列确认为预期的消旋分枝杆菌或脆弱分枝杆菌。这满足了科赫的假设。因此,分离株GZ20190123被鉴定为消旋分枝杆菌,GZ20190124被鉴定为脆弱分枝杆菌。以前,据报道,消旋分枝杆菌和脆弱分枝杆菌是番茄(Kwon和Hong2005)和葡萄上的病原体(Ghuffar等人。2018),分别。据我们所知,这是在中国西南部首次报道的假太子菌根腐病,这种疾病可能会对这种重要的药用植物的生产造成重大损失。
Radix pseudostellariae L. is one of the most common and highly-prized Chinese medicinal plants with various pharmacological effects, and mainly produced in acid soils in the Guizhou and Fujian provinces of southwestern and southeastern China, respectively (Wu et al. 2020). However, consecutive monoculture of R. pseudostellariae results in severe root rot and decline in biomass and quality of underground tubers. Root tubers of R. pseudostellariae are typically planted in December and harvested in next June. Root rot commonly starts developing in May. The disease incidence of root rot was ranging from 37 to 46% in root portions and basal stem of R. pseudostellariae under the consecutive monoculture fields in Shibing County, Guizhou Province, China (108°12\'E, 27°03\'N) (Li et al. 2017). Severe root rot was observed in Shibing County in May 2018. Infected plants displayed curly, withered, and yellow leaves, blight, retarded growth, root rot, and yield losses. Abundant whitish mycelia were observed on roots and surrounding soil. Two fungal isolates, designated GZ20190123 and GZ20190124, were obtained from symptomatic roots cultured on potato dextrose agar (PDA). The optimum temperature range for growth of the two isolates was 25 to 30°C. The optimum pH range for the growth of GZ20190123 was 5 to 5.5, whereas GZ20190124 grew better between pH 5 to 8.5. The mean mycelial growth rates of GZ20190123 and GZ20190124 at 30°C were 2.1 and 1.5 cm/day, respectively. Conidia of the two isolates were ovoid or obclavate and were produced in single or branched chains. The internal transcribed spacer (ITS) region was amplified with primers ITS1 and ITS4 (White et al. 1990). The sequences were deposited in GenBank as accession No. MN726736 for GZ20190123 and MN726738 for GZ20190124. Sequence comparison revealed 99% (GZ20190123) and 97% (GZ20190124) identity with previously reported isolate xsd08071 of Mucor racemosus Bull. (accession No. FJ582639.1) and isolate BM3 of Mucor fragilis Bainier (accession No. MK910058.1), respectively, which was confirmed by phylogenetic analysis. The two isolates were tested for pathogenicity on R. pseudostellariae. Six roots of R. pseudostellariae were surface-sterilized with 75% ethanol and stab inoculated with mycelia using a sterile toothpick for each isolate. Sterile distilled water was stab inoculated to twelve roots to serve as the control. Treated roots were incubated in a greenhouse with 16 h day length [light intensity 146.5 μmol/(m2·s)] and day/night temperature 26°C/18°C. The inoculated roots showed the expected symptoms on roots and sprouts 7 days after inoculation, whereas the control roots with sprouts did not show any symptom. The fungi were re-isolated from the diseased roots and confirmed as expected M. racemosus or M. fragilis based on the ITS sequences, which satisfied Koch\'s postulates. Thus, isolate GZ20190123 was identified as M. racemosus and GZ20190124 as M. fragilis. Previously, M. racemosus and M. fragilis have been reported as a pathogen on tomato (Kwon and Hong 2005) and grape (Ghuffar et al. 2018), respectively. To our knowledge, this is the first report of M. racemosus and M. fragilis causing root rot of R. pseudostellariae in southwestern China, where the disease could cause a significant loss to production of this important medicinal plant.