MySQL v5.1.73 - can the binlog_format betweem Master & slave be different?
The Error Message you received


  Last_SQL_Error: Could not execute Delete_rows event on table test.pruning; Can’t find record in ‘pruning’, Error_code: 1032; handler error HA_ERR_KEY_NOT_FOUND; the event’s master log mysql-bin.000002, end_log_pos 1448


This message can come up when doing a DELETE query with row-based replication. Unfortunately, it is one of the disadvantages to row-based replication:


  
  Disadvantages of row-based replication
  
  
  RBR can generate more data that must be logged. To replicate a DML statement (such as an UPDATE or DELETE statement), statement-based replication writes only the statement to the binary log. By contrast, row-based replication writes each changed row to the binary log. If the statement changes many rows, row-based replication may write significantly more data to the binary log; this is true even for statements that are rolled back. This also means that taking and restoring from backup can require more time. In addition, the binary log is locked for a longer time to write the data, which may cause concurrency problems.


I have addressed something similar (error 1032 in my answer to 
MySQL master master replication, safe to delete rows on both masters?) where doing a DELETE query was the issue.

In your case, since the Slave is using STATEMENT, the row change is expected to be a precise match of PRIMARY KEYs between Master and Slave. On many occassions, it may not be the case. That is why error 1032 exists.

To play it safe,


use binlog_format=ROW on both Master and Slave
use binlog_format=MIXED on both Master and Slave
use binlog_format=STATEMENT on both Master and Slave
You could experiment with Master MIXED and Slave ROW. At the very least, avoid STATEMENT on the Slave if the Master is not STATEMENT.