Q: Can the editor make a decision based only on one reviewer's report?

Although it unusual for an editor to do so, the editor of a journal can make a decision about a manuscript submitted to that journal based on the report of only one reviewer. That said, a great deal depends on the details of the case. For instance, if the editor happens to be active in the same field as that represented by the manuscript and considers the manuscript worthy of being published, the report from a single reviewer can be sufficient: the editor, in effect, is the second reviewer. 

Much also depends on what the sole reviewer has expressed in the report: if the reviewer recommends early publication keeping in mind that the field is rapidly advancing and priority is important, and if the editor agrees with this assessment, the editor may decide to go ahead and publish the manuscript. On the other hand, if the editor and the reviewer disagree on the merit of the manuscript, the editor is unlikely to make the final decision based on only a single review. 

To sum up, the editor’s decision will be based on multiple considerations: 

• Agreement (or disagreement) between the sole reviewer and the editor 
• The editor’s familiarity with the contents of the manuscript 
• Urgency (whether the contents are such that early publication is required 
• Likelihood of getting another review quickly 
• The results reported in the manuscript (whether routine, of incremental value only, or of fundamental importance, challenging accepted knowledge or interpretations.