Tewoldemedhin Y T, Lamprecht S C, McLeod A, Mazzola M
University of Stellenbosch, Department of Plant Pathology, Matieland 7602, Stellenbosch, South Africa.
University of Stellenbosch, Department of Plant Pathology and Plant Protection Research Institute (ARC), Private Bag X5017, Matieland 7599, Stellenbosch, South Africa.
Plant Dis. 2006 Nov;90(11):1399-1406. doi: 10.1094/PD-90-1399.
Isolates of Rhizoctonia spp. associated with barley, canola, clover, lucerne, lupin, annual Medicago spp. (medic), and wheat were recovered during the conduct of a 4-year (2000 to 2003) crop rotation trial in the Western Cape province of South Africa. These isolates were characterized by determining their anastomosis group (AG), in vitro optimum growth temperature, and pathogenicity toward emerging and 14-day-old seedlings of all the aforementioned crops. During the 4-year rotational trial, 428 Rhizoctonia isolates, in all, were obtained. The most abundant multinucleate AG was AG-4 HG-II (69%), followed by AG-2-1 (19%), AG-3 (8%), AG-2-2 (2%), and AG-11 (2%). The population of binucleate Rhizoctonia spp. comprised AG-K (53%), AG-A (10%), AG-I (5%), and unidentified AGs (32%). The optimal time for isolating Rhizoctonia spp. was found to be at the flowering or seedpod stage (20 to 22 weeks after planting). Temperature studies showed that isolates belonging to AG-2-2, AG-4 HG-II, and AG-K had significantly higher optimum growth temperatures than those from other AGs. In pathogenicity assays conducted on emerging as well as 14-day-old seedlings, isolates of AG-2-2 and AG-4 HG-II were the most virulent on all crops. Rhizoctonia solani AG-2-1 was highly virulent on canola, moderately virulent on medic and lupin, weakly virulent on lucerne and barley, and nonpathogenic on wheat. AG-11 isolates were moderate to weakly virulent on all crops, with the exception of barley and wheat. AG-3 was weakly virulent on canola, lupin, and medic. AG-K was the only binucleate Rhizoctonia sp. capable of inciting disease in our assays. This is the first comprehensive study to elucidate the identity and potential importance of Rhizoctonia spp. as a yield limiting factor in crop production systems in the Western Cape province of South Africa.
在南非西开普省进行的一项为期4年（2000年至2003年）的作物轮作试验中，分离出了与大麦、油菜、三叶草、苜蓿、羽扇豆、一年生苜蓿属植物（苜蓿）和小麦相关的丝核菌属菌株。通过确定其融合群（AG）、体外最适生长温度以及对上述所有作物的新出现和14日龄幼苗的致病性，对这些分离株进行了表征。在为期4年的轮作试验中，总共获得了428株丝核菌分离株。最丰富的多核AG是AG-4 HG-II（69%），其次是AG-2-1（19%）、AG-3（8%）、AG-2-2（2%）和AG-11（2%）。双核丝核菌属的群体包括AG-K（53%）、AG-A（10%）、AG-I（5%）和未鉴定的AG（32%）。发现分离丝核菌属的最佳时间是在开花期或结荚期（种植后20至22周）。温度研究表明，属于AG-2-2、AG-4 HG-II和AG-K的分离株的最适生长温度显著高于其他AG的分离株。在对新出现的以及14日龄幼苗进行的致病性试验中，AG-2-2和AG-4 HG-II的分离株对所有作物的毒性最强。立枯丝核菌AG-2-1对油菜毒性高，对苜蓿和羽扇豆毒性中等，对苜蓿和大麦毒性弱，对小麦无致病性。除大麦和小麦外，AG-11分离株对所有作物的毒性为中等至弱。AG-3对油菜、羽扇豆和苜蓿毒性弱。AG-K是我们试验中唯一能够引发疾病的双核丝核菌属物种。这是第一项全面研究，阐明了丝核菌属作为南非西开普省作物生产系统中产量限制因素的身份和潜在重要性。
