text: The 24-hour industrial action is part of an ongoing dispute over staffing and the role of conductors.
  A strike planned for 4 April on Southern routes was moved to 8 April after the company offered fresh talks.
  Merseyrail said coinciding a strike with the race meeting would damage Liverpool's reputation.
  Speaking after its failed talks with the union on Monday, Merseyrail's managing director Jan Chaudhry-van der Velde said the strikes would "do immeasurable damage" as the "eyes of the world will be on Liverpool" during the Grand National.
  RMT general secretary Mick Cash said the "cynical and hostile stance from Merseyrail" left the union "with no option but to put on this additional strike action".
  He said the RMT "recognises the severe impact that the action will have" but asked the public "to understand that we have no option but to take this high-profile action to force the company back to the negotiating table".
  Mr Chaudhry-van der Velde said the RMT "has sunk to a new low" by inflicting "a barefaced attack on the reputation of our region" on "one of its proudest and most important days of the year".
  Merseyrail has "a range of contingency plans" which would "almost inevitably involve using buses to replace trains", he said.
  Mr Cash called on Southern to "get out of the bunker and to start making some progress".
  He said RMT members on Southern "have shown incredible strength and resilience throughout the past year" and "have been clear from the off that this is not a dispute about who opens the doors".
  "It is a dispute about a safe method of operation and about the guarantee of that crucial, second safety-critical member of staff," he said.
  A Southern spokesman said: "We have received no official confirmation from the RMT and will review our response when we do."
  Richard Allan, deputy managing director of Arriva Rail North, said he was "surprised" at the move as "we had been in contact with their officials in the last 24 hours to organise further talks".
  David Sidebottom, director of independent watchdog Transport Focus, said: "Yet more strikes are being dumped on passengers who may have to cancel plans or endure miserable journeys.
  "It is vital that all parties in this dispute get back around the table to resolve this matter without bringing the railway to a standstill."
  Up to 2,000 staff at Southern rail, Merseyrail and Northern rail walked out on 13 March in the ongoing dispute but only limited disruption was reported.
target: Workers on Southern, Merseyrail and Arriva Trains North are to hold fresh strikes on 8 April, the day of the Grand National, the RMT union has said.