Proposition 37, which would have required labeling of genetically modified foods, was soundly defeated Tuesday.

The measure trailed 53 percent to 47 percent with more than 98 percent of the vote counted as of 6:00 a.m Wednesday.

Proposition 37 advocates relied on social media and a strong grass-roots campaign in hopes of making California the first state in the nation to require a “genetically modified” label on a host of food products, from breakfast cereals to tofu.

But supporters were outgunned by a highly organized “no” campaign, which poured $46 million into defeating Proposition 37 and blanketed the state with advertising.

The yes campaign raised $9.2 million, with the largest contribution coming from Joseph Mercola, a popular holistic health activist from Illinois.

The no side raised $46 million and spent nearly $27 million on radio, television and Internet advertising across the state. St. Louis-based Monsanto, a leading maker of genetically engineered seeds, was the largest single contributor with $8.1 million.

“Well, friends, it looks like Monsanto has done it again. Lied, cheated, deceived and hoodwinked enough of the electorate to pull the rug out from under us,” read a long post on the Yes on Prop on 37 campaign’s Facebook page. “We’ll need to pick ourselves up and shake the dust off and keep moving forward.”

The battle over Proposition 37 was an unusually high-profile fight because it pitted businesses against businesses. Big natural-food companies, celebrity chefs and several organic farmers were on one side, while a variety of traditional farmers and chemical, seed and processed-food firms were on the other.

The No on 37 campaign argued that the measure was “flawed and misguided,” messaging that appeared to work.

“California family farmers can breathe a little easier today,” said Jamie Johansson, an Oroville farmer who grows olives and makes olive oil and was active in the No on 37 campaign. “Prop. 37 would have imposed costly new regulations on California family farmers that no other state requires, putting us at a competitive disadvantage. Thankfully voters understood this and rejected Prop. 37 and voted instead to protect family farmers.”

Contact Dana Hull at 408-920-2706. Follow her at Twitter.com/danahull.