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ARS Home » Northeast Area » Ithaca, New York » Robert W. Holley Center for Agriculture & Health » Emerging Pests and Pathogens Research » Research » Publications at this Location » Publication #357740

Research Project: Characterization of Molecular Networks in Diseases Caused by Emerging and Persistent Bacterial Plant Pathogens

Location: Emerging Pests and Pathogens Research

Title: First report of Rhizopus oryzae causing Potato Soft Rot in the Hebei Province of China

item Swingle, Bryan
item CUI, W. - Chinese Academy Of Sciences
item ZHENG, H. - Inner Mongolian Agriculture University
item ZHANG, F. - Chinese Academy Of Sciences
item ZHU, H. - Chinese Academy Of Sciences
item GAO, M. - Chinese Academy Of Sciences

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2018
Publication Date: 2/18/2019
Citation: Swingle, B.M., Cui, W.G., Zheng, H.L., Zhang, F.B., Zhu, H.T., Gao, M. 2019. First report of Rhizopus oryzae causing Potato Soft Rot in the Hebei Province of China. Plant Disease. 104.

Interpretive Summary: Here we report the discovery of a new cause of potato soft rot disease. We found Rhizopus oryzae, a pathogen not normally associated with potato soft rot, in diseased potato plants growing in two fields in Guyuan County, Hebei Province of China. The pathogen was isolated from the diseased plants and confirmed to be Rhizopus oryzae based on its spore shapes, its growth appearance on agar medium and its genes. The pathogen was confirmed to be pathogenic by its ability to cause disease after it was used to inoculate healthy plants and was subsequently re-isolated from the diseased tissue, thereby providing the formal evidence that this organism was responsible for the disease.

Technical Abstract: Rhizopus soft rot occurs on the succulent tissues of vegetables, fruits and ornamental plants throughout the world. In September 2016, a disease outbreak in potato suspected as Rhizopus soft rot occurred in two fields in Guyuan County, Zhangjiakou City, Hebei Province of China. There were soft water-soaked lesions on the surface of diseased tubers, and the interiors were black and soft. Infected plants were sampled to isolate and determine the identity of the disease-causing organism. We isolated 15 white colonies that became brownish-grey to blackish-grey and developed densely packed mycelium. One colony was isolated (MLS-22-1-z15) for identification. Under the microscope, we observed non-septate rhizoids, sporangia and unequal, irregular, sub-globose or oval sporangiospores. We analyzed the sequence of the internal transcribed spacer (ITS) region between genes coding for the large and small rRNA genes and found this sequence was 100% identical to that of Rhizopus oryzae. To complete Koch’s postulates, we inoculated healthy tubers with isolate MLS-22-1-z15 using a wound inoculation method and found that it produced symptoms similar to that observed in the field grown potato plants. We then re-isolated the disease-causing organism and found it to be identical to the isolate used to infect the plants. In total, the data presented support the hypothesis that Rhizopus oryzae was responsible for the observed soft rot disease.