"He is not a vegetable," states the claim to restrain Martyn Namorong "from further writing (printing) or causing to be written (printed, broadcast) or otherwise publishing of the plaintiffs the alleged, or any similar libel".
Mr Gamato is seeking punitive and aggravated damages for "stress, anxiety and loss of reputation" and a costs order.
National Court Justice Collin Makail last week ordered the "Statement of Claim" be published in newspapers and the case return to court on July 25, when election writs are due to be returned.
"He made some defamatory statements and also called my surname, which is Gamato as 'tomato'," the ABC reported Mr Gamato as saying at a press conference in the capital Port Moresby last Friday.
"I don't look like a tomato, I'm a human being.
"He put a big tomato on my head, what if he did that to you?"
Election turmoil in PNG has seen Mr Gamato criticised on social media for the conduct of the election.
“On or about 27 June 2017 in the (sic) Defendant wrote or published in his tweeter (sic) account by calling the Plaintiff as (sic) Mr Tomato, the defendant maliciously wrote and published in his tweeter account and these (sic) has gone viral on social media in particular Facebook by tarnishing the surname of the Plaintiff (Gamato),” the statement of claim signed by Kemno’nga Robin Kawat of Kawat Lawyers published in The National newspaper said.
“The publication ... by calling him Tomato has tarnished his reputation in the way of his occupation, profession and office the Plaintiff occupies and in relation to his conduct therein) (sic) the following defamatory words.”
Five tweets are reproduced in the statement referring to “Tomato”, “#ELECTIONfraud” and the discovery of 184,300 Kina (A$73,000) on returning officers, “revenge politics” over students being denied “the right to vote”, ties to the incumbent prime minister Peter O’Neill’s People’s National Congress party and calls for him to resign.
Mr Gamato claims he was defamed by being called unqualified, accused of mismanaging the elections, politically compromised and that he “conspired to rig the elections”.
Mr Namorong has posted photos on his social media accounts of him gagged or drinking beer.
After initially posting he needed a lawyer, in a recent comment on Saturday Mr Namorong states: "I'm fine".
A Commonwealth election observer's report last week said “all aspects” of the election process needed to be reviewed, reporting "widespread" electoral roll irregularities, late starts to polling and other issues.
It added the observers were “disappointed” recommendations made after the 2012 election had not been implemented.
Tomatoes are botanically not classified as vegetables.