Ronald G. Segel, 56, chairman and chief executive of the publishing company that produces Variety and Daily Variety. A native of Boston and graduate of Harvard Business School, Segel first practiced as a certified public accountant. In 1971, he took a position as vice president of finance for Cahners Publishing Co., which now produces the two entertainment industry trade papers. The company, which publishes more than 50 industry-related papers, purchased Variety and Daily Variety in 1987. Earlier this year, Segel was named to the top post at Cahners, and appointed deputy chief executive of its parent company, Reed International P.L.C. of London. In Boston on Friday of lung cancer.