TOKYO, Japan — Sumo wrestling has been dealt a blow from which it may never fully recover.

The Japanese sport, still reeling from a gambling scandal last summer, is now confronting the most damaging allegation in its 1,500-year history: match-fixing.

The admission last week by three wrestlers that they had agreed to fix matches via mobile phone is a bombshell that, sumo experts say, may relegate sumo from national sporting obsession to sideshow.

The claims are so serious that the Japan Sumo Association, the sport’s governing body, on Sunday canceled next month’s tournament in Osaka — the first such cancellation for more than half a century. The last time it happened, in 1946, organizers were at least able to cite wartime bomb damage to the tournament venue.

The cancellation could cost the association 1.3 billion yen ($15.8 million) in lost revenue, including 720 million yen in ticket sales, the Sports Nippon newspaper said.

Hanaregoma, the association's chairman, described the scandal as the darkest chapter in sumo history.

"We cannot, and should not hold the tournament under these circumstances," he told reporters. "Until we can completely root out corruption on the sport, we cannot appear in the sumo ring. We will do everything we can to establish the facts as quickly as possible."

Sumo’s latest dalliance with disgrace began late last week, when reports emerged that incriminating messages had been found on mobile phones belonging to several wrestlers.

The phones had been confiscated last summer during a police investigation into separate allegations that scores of wrestlers had bet illegally on professional baseball games, with members of Japan’s underworld acting as bookmakers.

That case has led to four arrests and the expulsions of a former champion wrestler and a coach. In all, more than 60 wrestlers, practitioners of a sport once revered for its commitment to fair play, have admitted betting on baseball, cards, golf and mahjong.

This time, at least a dozen wrestlers are suspected of agreeing how certain bouts would unfold, and how much money should be paid to the defeated opponent. Some messages reportedly contained bank account details.

This year was supposed to be the catalyst for a purge of sumo’s worst offenses: its opaque, old-fashioned style governance; the systematic bullying of young trainees; and serial transgressions ranging from marijuana use to drunken brawls.

While allegations of match-fixing have dogged sumo for years, nothing could prepare it for the latest revelations.

The story has dominated domestic media for days; even the prime minister, Naoto Kan, felt moved to offer an opinion. “Sumo has a long history and a great number of fans," he told parliament. "It is certainly the national sport. If matches have been fixed, it is a serious betrayal of the people."

The names of nine wrestlers, including four in the highest division, appeared in the messages, Japanese media said, adding that the going rate for throwing a match was about 200,000 yen, with one wrestler involved apparently demanding 500,000 yen.

In one message, the sender confirmed he would hit his opponent “head on,” while others contained references to cash sums: "For 20 more I will concede,” one said. “After the meet, I need to make at least 50 [thousand yen] or I'll be in serious trouble."

The motive appears to be professional, as well as financial. Wrestlers must aim to end each 15-day tournament – six of which are held every year – with a greater number of victories than defeats to ensure their progress up the rankings or, at the very least to avoid demotion. Once they slip into the third-tier makushita division, they lose a large part of their salaries and the perks that come with competing at the top.

Police, though, are not expected to launch a criminal investigation. Match-fixing is not illegal, and there is no evidence that anyone bet on the outcomes of rigged bouts.

But there are victims: the fans, who despite the rumors, wanted to believe that the men engaged in gargantuan struggles in the ring were inspired by nothing more than a shared desire to win. And the vast majority of sumo’s 600-plus wrestlers, who would no sooner throw a match than forego their daily intake of chanko stew.

The education minister, Yoshiaki Takaki, who has responsibility for the sport, said the sumo association could lose its preferential tax status as a government-affiliated body. "If the media reports are true, we have to consider taking severe measures," he said.

And if high-ranking wrestlers are named, it could destroy sumo’s status as a major sport, said Mark Buckton, who writes about sumo for the Japan Times.

“This is hugely damaging,” he said. “Sumo looks like it is going to lose its preferential tax status, which will hurt it financially. Attendances are already down, so this could be the final nail in the coffin that turns sumo into a side sport.”

Buckton believes sumo’s future as a popular sport hinges on the outcome of the association’s investigation, which could take weeks. If proof emerges that famous wrestlers from the top division fixed matches, he said, “That’s when I expect the collapse to come.”

This is not the first time the sport has been accused of impropriety. Last October, the supreme court ordered a publisher to pay 44 million yen to the sumo association and three wrestlers for linking them to match-fixing in a magazine article. Similar claims have been surfacing for years, but none has ever prompted an investigation, let alone an admission of culpability among active wrestlers.

In addition to last summer’s gambling scandal, sumo’s reputation has been hit by marijuana use among wrestlers, its links with the underworld and the bullying of young trainees, which in 2007 resulted in the hazing death of a 17-year-old wrestler.

Japanese newspapers were united in their condemnation. The Asahi Shimbun said the claims had tested fans’ patience to a breaking point. “Despite its various problems, many people continue to love sumo,” the newspaper said. “But this time, it may not be easy to win back the hearts of fans who have completely lost faith in the sport.”