Masuka A J
Kutsaga Research Station, P.O. Box 1909, Harare, Zimbabwe.
Plant Dis. 1998 Feb;82(2):263. doi: 10.1094/PDIS.1998.82.2.263A.
Rhizoctonia solani Kühn (teleomorph Thanatephorus cucumeris (A. B. Frank) Donk) anastomosis groups AG 4 and AG 3 cause, respectively, widespread stem rot and leaf spot diseases of tobacco in Zimbabwe (2). Stem rot leads to substantial field losses, necessitating routine chemical and biological control (1). A recent increase in reports on Rhizoctonia-induced damping-off in tobacco seedlings and lodging of mature field plants prompted detailed studies on the causal pathogen. Nuclear fluorescence microscopy studies of 83 isolates from diseased tobacco revealed the presence of binucleate isolates. The isolates were collected in 1981 (1 isolate), 1990 (1 isolate), 1996 (3 isolates), and 1997 (1 isolate) and caused damping-off in seedlings (2 isolates) and stem rot and lodging in field tobacco (4 isolates). We confirmed that all binucleate isolates contained only two nuclei per cell. There was variability in the number of nuclei among the multinucleate stem rot (mean 4.2, SE 0.265) and leaf spot (mean 7.5, SE 0.259) isolates. Two tested binucleate Rhizoctonia isolates were pathogenic to 7-week-old tobacco seedlings (cv. Kutsaga 35) in a greenhouse experiment, laid out as a randomized complete block design. Uninoculated healthy plants served as control. Based on a disease rating scale of 1 to 5 (1 = no disease and 5 = >50% stem damage), overall disease incidence was 88.9% 5 days after inoculation with macerated mycelium at the rate of 3.60 × 10 CFU per seedling, applied around the stem base. Over 50% of inoculated seedlings were rated in disease categories 4 and 5. Binucleate Rhizoctonia were consistently isolated from infected plants. A country-wide survey is being conducted to determine the incidence, distribution and severity of diseases caused by binucleate Rhizoctonia on tobacco in Zimbabwe. References: (1) J. S. Cole and Z. Zvenyika. Plant Pathol. 37:271, 1988. (2) S. I. Mpofu and A. M. Julian. J. Phytopathol. 140: 367, 1994.
立枯丝核菌库恩（有性型为瓜亡革菌（A. B. 弗兰克）唐克）的融合群AG 4和AG 3分别在津巴布韦引发了烟草广泛的茎腐病和叶斑病（2）。茎腐病导致田间大量损失，因此需要进行常规的化学和生物防治（1）。最近，关于立枯丝核菌引起烟草幼苗猝倒病以及成熟田间植株倒伏的报道增多，促使人们对致病病原菌展开详细研究。对83株来自患病烟草的分离株进行的核荧光显微镜研究显示存在双核分离株。这些分离株于1981年（1株）、1990年（1株）、1996年（3株）和1997年（1株）采集，可导致幼苗猝倒病（2株）以及田间烟草的茎腐病和倒伏（4株）。我们证实所有双核分离株每个细胞仅含有两个细胞核。多核茎腐病分离株（平均4.2个，标准误0.265）和叶斑病分离株（平均7.5个，标准误0.259）的细胞核数量存在差异。在一项温室试验中，将两个经过测试的双核立枯丝核菌分离株按照随机完全区组设计接种到7周龄烟草幼苗（品种Kutsaga 35）上。未接种的健康植株作为对照。根据1至5级的病害评级标准（1 = 无病害，5 = 茎部损伤>50%），以每株幼苗3.60×10 CFU的菌丝体匀浆在茎基部周围接种5天后，总体发病率为88.9%。超过50%的接种幼苗被评为4级和5级病害。从受感染植株中持续分离出双核立枯丝核菌。目前正在进行一项全国性调查，以确定津巴布韦由双核立枯丝核菌引起的烟草病害的发病率、分布情况和严重程度。参考文献：（1）J. S. 科尔和Z. 兹韦尼卡。《植物病理学》37:271，1988年。（2）S. I. 姆波富和A. M. 朱利安。《植物病理学杂志》140: 367，1994年。
