During the last decade of the 19th century, the Populists were the most prominent reformers in the United States. Although they died out in that same decade, some of their ideas lived on with the Progressives. The Progressives took many of the Populists' ideas, but they went beyond those ideas to become involved in many types of reforms that the Populists did not have in mind.
The main reforms that the Progressives took up were reforms that were aimed against the powers of the big businesses. For example, the "trustbusting" of Theodore Roosevelt came from Populist ideas. As the "salem-history" link says, Populist
farmers believed that they were at the mercy of monopolies and speculators, and they demanded government legislation regarding the control of money, transportation, and land.
However, the Progressives went well beyond this sort of reform. For example, they were interested in political reforms (breaking the power of urban machines) and in social reforms (Prohibition). These were types of reforms that were not prominent in the Populist agenda.
Some of the Populist agenda (crackdowns on the power of big business) did become part of the Progressive agenda. However, many of the Progressives' reforms were new with them and were not extensions of the previous reformers' efforts.