論文發表人:陳其敏(加州大學河濱校區/Plant Pathology and Microbiology Department)
http://www.ag.ndsu.nodak.edu/aginfo/barleypath/rhizoc/meeting.htm
Waitea circinata var. circinata (Wcc) 於2003年被發現在美國東部，美西以及中西部的數十個高爾夫球場引起嚴重草坪病害brown ring patch◦ 根據本研究Wcc是Rhizoctonia的有性世代之一，許多的Rhizoctonia spp能感染禾本科葉部或根部造成植株死亡◦ 早熟禾屬的annual bluegrass (Poa annua)以及rough bluegrass (Poa trivialis)已被報導可被Wcc感染，這兩種草種在美國被廣泛的應用於草坪植被，尤其是高爾夫球場◦ 在這份研究中，藉由分子生物技術 (rDNA ITS序列和RFLP [Restriction fragment length polymorphism])以及形態鑑定，確認由全美各地蒐集的42個病害樣本均被Wcc感染，同時這些樣本的rDNA ITS序列顯示出高度的歧異，指出此病原菌並非如預期的是近期傳入，實際上可能已經存在美國境內很長一段時間◦ rDNA ITS序列經過解析以及基因選殖，根據五個核酸位置的核酸變異 (三個heterozygosities 以及兩個indels) ，這四十二株樣本可被歸類為十八種變異種◦然而，這十八個變異種與其地理分布並無任何關連◦本研究同時證實雖然菌落形態鑑定以及分子鑑定有不同程度的變異，但變異程度不大，因此上述兩項鑑定方法仍然足以做為病害鑑定之依據◦
Brown ring patch, caused by Waitea circinata var. circinata (Wcc), is an emergent disease of annual bluegrass (Poa annua) and rough bluegrass (Poa trivialis) in the U.S. Since 2003, it has been reported in multiple locations in the western, mid-western and northeastern U.S. The objective of this study was to confirm the identity of pathogen from 42 isolates collected from these diverse locations using colony morphology, and RFLP and sequence analyses of the rDNA-ITS region. The colony morphology of collected isolates was distinct from other anamorphs of Waitea circinata (Rhizoctonia oryzae and R. zeae), but bulbil color and morphology were variable on PDA with 2-mm to 5-mm diameter bulbils ranging from dark brown to orange to white being produced after 28 days in culture. RFLP analysis of ITS1F-ITS4 amplified regions followed by digestion with HapII produced RFLP unique patterns not previously reported from studies with Wcc in Japan and California. Additional sequencing of multiple clones of the amplified ITS region for the 42 isolates, revealed heterozygosity, the presence of poly-nucleotide indels and other sequence variation between isolates. A total of 18 ITS haplotypes were found and there was no association of the haplotypes with geographic distribution. Results from this study indicate that colony morphology and rDNA-RFLP analysis can be more variable than previously reported, and that this variation should be taken into account for identification and diagnosis. The sequence diversity of the amplified ITS-region, the presence of heterozygous sites and indels, provides some measure of genetic diversity of Wcc in the U.S. and suggest that the pathogen has been present in the U.S. for a time and is not a recent introduction to turfgrass. Further studies using additional markers or methods are needed to more adequately address this aspect of the population biology of Wcc.
