金钗石斛和铁皮石斛软腐病原菌的分离和鉴定

The Isolation and Identification of Pathogen of Dendrobium nobile and Dendrobium candidum Damping-off Disease

目的确定引起金钗石斛和铁皮石斛软腐病的病原菌,为制定高效、安全的防治措施提供依据。方法采用普查和定点观察相结合对软腐病发病情况进行田间观察,采集两种石斛典型病株样本,按照柯赫氏法则对其病原菌进行分离、纯化、菌株鉴定及致病性测定。结果在树皮为基质的苗床上软腐病在不同苗龄上均可发生,病原菌主要侵染幼嫩多汁的嫩芽和新枝,引起幼嫩茎叶的腐烂、萎焉和坏死等症状。通过对病原菌形态学观察,以及核糖体rDNA ITS序列分析,侵染石斛植株的2个分离菌株被鉴定为终极腐霉Pythium ultimum。致病性实验证明,这两个菌株为石斛软腐病的致病菌株。结论金钗石斛和铁皮石斛是终极腐霉菌的自然寄主。

OBJECTIVE To ascertain the causal agent of Dendrobium nobile and Dendrobium candidum damping-off, and provide basis for the establishment of efficient and safe preventative measures. METHODS Observe the disease in fields through general in- vestigation and fixed point observation. In accordance with Koch＇s postulation the isolation and identification of pathogen and pathoge- nicity tests were performed after collecting the typical diseased plants. RESULTS The disease could occur on different aged plants in hark bed. Tender and juicy buds and new branches were infected usually, it resulted in rot,wilting, necrosis, etc.. Morphology obser- vation and analysis of rDNA ITS sequence confirmed that two isolates were both Pythium ultimum. Pathogenicity tests proved that P. ultimum was the causal agent of D. Mobile and D. candidum damping-off. CONCLUSION D. Mobile and D. candidum are natural hosts of P. ultimum.