中国木薯白点病发生调查及病原生物学特性研究

2007—2018年,本课题组在对中国木薯主栽区的病害调查中发现了一种国内尚未记载的叶斑病。病害主要危害叶片,形成圆形或不规则形、常密集分布的白色至黄褐色的病斑,故命名为白点病。该病在云南、海南、广西等地区均有发生,绝大多数主栽品种和部分新育成种质均受害。经病菌分离和回接实验以及病菌形态观察、核糖体基因间隔区和β-微管蛋白基因序列分析,将该病病原鉴定为链格孢(Alternaria alternata)。病菌离体培养实验表明,菌丝生长最适条件为V9、OA、CA或CMA培养基,28℃,D-麦芽糖、D-山梨醇或D-乳糖,硝酸钠,光暗交替,pH8。分生孢子萌发最适温度为28℃,而致死温度为60℃处理5min。杀菌剂敏感性测定结果表明,在所测试的10种药剂中,10%苯醚甲环唑WG和25%吡唑醚菌酯WG的EC50值分别为0.12、0.47 mg/L,对菌丝生长抑制率最高。

Survey,Pathogen Identification of a White Spot Disease on Cassava and Its Biological Characteristics in China

During cassava disease survey from 2007 to 2018, one new leaf spot disease was found in the main cassava planting areas of China. The pathogen mainly infected the cassava leaves with densely formed round or irregular, white to tawny lesions. The disease was widely happened in Yunnan, Hainan, Guangxi and some other provinces, and most of the main cassava planting varieties and part of late breeding germplasms were also infected. The results of pathogen isolation, pathogenicity test, strain morphology observation, sequences analysis of Internal Transcribed Spacer and beta-Tubulin gene showed the disease was caused by Alternaria alternata. The pathogen in vitro cultured showed V9, OA, CA or CMA medium, 28 ℃, D-maltose, D-sorbitol or D-lactose, NaNO₃, alternative light and pH 8 were the optimum conditions for mycelial growth. The optimum temperature for conidia germination was 28 ℃ and the lethal temperature for conidia was 60 ℃ remained for 5 min. Sensitivity test confirmed 10% difenoconazole WG and 25% pyraclostrobin WG had the best mycelium inhibition effect from 10 fungicides, and the EC₅₀ value was 0.12 mg/L and 0.47 mg/L, respectively.