BOSTON — "Take five." "Reward yourself with a high five." "Five a day."Five was a magic number here at the Produce Marketing Association (PMA) convention last week. Leaders of the produce industry have kicked off a nationwide campaign to encourage people to eat more fruits and vegetables - five servings a day. The industry has taken a cue from government agencies, such as the United States Department of Health and Human Services and the National Academy of Sciences, that advocate a moderate, balanced diet rich in fruits and vegetables. Their goal is to increase Americans' consumption of fruits and vegetables from 2.5 daily servings per person to five servings by the year 2000. The campaign has brought a certain unity to the produce industry, which has historically been fragmented unlike, say, the dairy or beef industries. "The [produce] industry has always wanted to come together," says Kathy Means, spokeswoman for PMA, "This has got to be the most significant push." When celery and carrot sticks can be found at McDonald's and more and more restaurants feature salad bars, the industry has picked an opportune time to promote generic produce. If all goes as planned, consumers become familiar with "five" theme at supermarkets, on television, and in school cafeterias.